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J. Crop Sci. Biotech. 2017 (March) 20 (1) : 45 ~ 60 DOI No. 10.1007/s12892-016-0093-0 RESEARCH ARTICLE

Sunflower Allelopathy for Weed Control in Agriculture Systems Lakhpat Singh Rawat*, RK Maikhuri, Yateesh M Bahuguna, NK Jha, PC Phondani G.B. Pant National Institute of Himalayan Environment and Sustainable Development, Garhwal Unit, Srinagar Garhwal, Uttarakhand, India Received: October 28, 2016 / Revised: December 11, 2016 / Accepted: February 15, 2017 Ⓒ Korean Society of Crop Science and Springer 2015

Abstract Recent developments in weed science and allied aspects have involved several interdisciplinary approaches. In this context, indiscriminate use of herbicides for weed control has become a questionable subject, which besides controlling the weeds, the chemical herbicides are harmful in many ways to soil, crops, other plants and the environment as a whole. Taking into consideration ecologically sound weed management, in modern days the reliance on chemical herbicides has decreased and a shift towards naturally occurring biological herbicides has received great attention throughout the world. Sunflower is an annual dicotyledonous plant, herbaceous, erect, and a native of North America. It is thermo and photo-insensitive, hence it can be grown year round in sub-tropical and tropical countries. Only two spp. Helianthus annuus L. and Helianthus tuberosum are cultivated for food, the remaining spp., are ornamentals weeds and wild plants. However, H. annuus is allelopathic and inhibits the growth and development of other plants thus reducing their productivity. Sunflower is a major oil-yielding crop in India and its cultivation in northwest India started 25 to 30 years ago in areas located in the plains. In this region, rice-wheat rotation became very popular owing to its high yields; however, these crops are highly infested by weeds, thus farmers use herbicides for their control. Hence, this rotation consumes a maximum quantity of herbicides in this region, which has resulted in several problems viz., environmental pollution, human health hazards, and development of herbicide resistance in weeds. Thus, serious ecological questions about the reliance on herbicides for weed control in this rotation have been raised. One of the alternatives to overcome these problems is with the use of allelopathic strategies, including the use of weed-smothering crops for weed management and for the sustainability of agriculture. The field, pot culture, and laboratory studies have shown that inclusion of sunflower crops in rotation and intercropping considerably reduced the weed population in the current and succeeding crops. Rhizosphere soil of sunflower drastically smothered the weed germination, population, and biomass. The residual suppression effect of sunflower also persisted in the next crop up to 75 days. Thus, it is conceptualized that the inclusion of such oilseed crops before the rice crop in the rice-wheat rotation may provide satisfactory weed control in the succeeding rice crops and may minimize the use of herbicides. Likewise, the replacement of sorghum by summer sunflower oilseed crops may also help in the control of summer as well as winter weeds. More studies in this direction may provide avenues for satisfactory weed management in agro-ecosystems and may help to minimize the use of herbicides and thereby pave the way to develop sustainable agricultural practices for biodiversity conservation and enhancing biological integrity. Key words : Allelopathy, allelochemicals, sunflower, crops, weeds, interaction, inhibition

Introduction Crops have been grown since ancient times without damage to the environment but the use of herbicides during the short span of the last 50 years have raised serious doubts Lakhpat Singh Rawat () Email: [email protected] Tel: 91+01346-252603 / Fax: 91+01346-252063

The Korean Society of Crop Science

about their continuous use. Thus, for sustainability, future weed control practices must minimize or stop the use of herbicides and use allelopathic strategies and other practices for weed management. Sustainable agriculture aims at long-term maintenance of natural resources and agricultural productivity with minimum adverse impact on the environment.

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It emphasizes optimal crop production with minimal external inputs, reducing dependence on commercial inputs (fertilizer and pesticides), and substituting them with internal resources and relying on sustainable practices, which maintain the productivity over long periods (Narwal 1996). The term 'allelopathy’ is derived from two Greek words “allelon” means each other and “pathos” meant to suffer i.e., the injurious effect of one upon another (Narwal 1994). However, Molisch coined this term in 1937, which refers to all biochemical interactions (stimulatory and inhibitory) among plants including microorganisms, through release of allelochemicals. The allelochemicals are secondary metabolites produced by plants for their self-defence against herbivores, predators, and pests (insects, nematodes, pathogens, etc.). These are released through leaching, exudation, volatilization, and death decay of plant or plant parts. In the latter case, soil microbes (actinomycetes, etc.) release the toxic agents from decomposing biomass. An alternative for overcoming herbicide related problems is to use allelopathic strategies in weed management for sustainable agriculture (Narwal 1997). These strategies include: a) using weed smothering crops, b) using crop residues for weed control, c) using phytotoxins from plants or microbes as herbicides, and d) using synthetic derivatives of natural products as herbicides. Since the allelopathic weed management strategies do not cause the problems associated with herbicides, efficient use of such strategies may lead to more sustainable agriculture. The allelopathic potential of sunflower for weed control has been reported in its cultivars viz., Ramsum HS-52, Peredovik, Hybrids 201, 8941. In greenhouse studies, the sunflower ‘Russian mammoth’ reduces both seed germination and biomass of weeds (Hall et al. 1982). The aqueous extracts as well as growing plants inhibit the seed germination and seedling growth of Abutilon theophrasti, Datura stramonium, Ipomoea species, and Brassica kaber (Dharmaraj and Sheriff 1994a, Dharmaraj et al. 1994b, Dharmaraj 1998; Leather and Forrence 1979; Prusty et al. 1994; Wilson and Rice 1968). Its aqueous extracts reduced the germination (36-56%) and seedling growth (22-57%) of Trianthema portulacastrum, Amaranthus viridis, and Parthenium hysterophorus. However, in field studies, a drastic reduction occurred in germination (83-95%), growth (79-95%), and chlorophyll content of above, weeds and also in Portulaca oleracea and Flaveria australasica weeds (Dharmaraj et al. 1994b, 1994c). sunflower-oat rotation over a 5-year-period significantly lowered the density of grassy and broadleaf weeds in fields than in control plots (Leather 1983a, 1983b). Although weed density increased in all plots over the five seasons, the rate of increase was less in sunflower plots. There was, however, little difference among the various sunflower cultivars. In further studies, weed biomass was equivalent in plots planted with sunflower, whether EPTC (S-thydipropyl carbomothiote) herbicide was applied or not, clearly showing the efficacy of sunflower-mediated weed control (Leather 1987).

The potential of sunflower as a source of allelochemicals is well known (Varela 1982) and bioassays of leaf aqueous extracts show strong inhibition and stimulation in germination and root length of test plant species. The leaf aqueous extracts of sunflower ‘SH 222’ were found to contain five new guananolides and the annuolides possess allelopathic activity of sunflower. All the guainolides possess allelopathic activity over dicotyledon species and are likely to be involved in the allelopathic activity of sunflower cultivars (Macias et al. 1993). In the similar line few of the allelochemicals viz., 16 sesquiterpene lactones, five flavonoides, four kaurenoed diterpenes, 14 bisnorsesquiterpenes and sesquiterpene heliannulos were absolutely charactrized (Macias et al. 1996a). The heliannuols proved inhibitory to dicot weed species hence, they may be an excellent source as -4 a pre and post-emergence herbicide at very low doses (10 -9 to 10 ). This type of research work is being done in developed countries to minimize or eliminate the use of present hazardous herbicides and replace them with eco-friendly herbicides based on natural plant products or allelochemicals. The generation of such information would help in: a) developing environmental friendly weed management practices to reduce the yield losses in field crops caused by the weeds and b) to overcome the problems associated with the present herbicides.

Allelochemicals Allelochemicals refer mostly to the secondary metabolites produced by plants and are byproducts of primary metabolic processes (Levin 1976). They have an allelopathic effect on the growth and development of the same plant or neighbouring plants. The term allelochemicals includes: a) plant biochemicals that exert their physiological/toxicological action on plants (allelopathy, autotoxicity, or phytotoxicity), b) plant biochemicals that exert their physiological/toxicological action on microorganisms (allelopathy or phytotoxicity), and c) microbial biochemicals that exert their physiological/toxicological action on plants (allelopathy and phytotoxicity). Secondary compounds are metabolically active in plants and microorganisms, their biosynthesis and biodegradation play an important role in the ecology and physiology of the organism in which they occur (Waller and Dermer 1981; Waller and Nowacki 1978). Some of them are accumulated at various stages of growth, while other depends upon time of day or season. Allelochemicals selectively inhibit the growth of soil microorganisms or other plants (or both). They play a role in chemical warfare between plants (allelopathic interactions) and include natural herbicides, phytotoxins (microbial inhibitors), and inhibitors of seed germination. Although many allelochemicals are strictly defence substances, others are offensive compounds that act directly in weed aggressiveness, competition, and the regulation of plant density. It is expected that in the near future many allelochemicals may be used commercially as herbicides, insecticides, nematicides, or

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as bioregulators. Allelochemicals most often impart plant resistance to insects, nematodes, and pathogens, besides following their release into the environment; some may regulate the distribution and vigour of plants. Most often plants come in contact with the allelochemicals in soil and their effect on crop plants may be modified by soil moisture, soil temperature, and other soil factors (Bhowmik and Doll 1983, Einhilling and Eckrich 1984; McCalla and Norstadt 1974; Patrick and Koch 1958; Patrick et al. 1964; Wang et al. 1967b). Some of the allelochemicals such as terpenoides and polyacetylenes may function in a volatile state, but most of the current research in agroecosystems involves water-soluble compounds. The known list of chemicals involved in allelopathy continues to expand and with better isolation and identification techniques, many new substances are being added.

plant communities. Plant parts known to contain allelochemicals (Rice 1974) are: a) roots and rhizomes, in general, contain fewer and less potent or smaller amounts of allelochemicals than leaves, but sometimes it may be the reverse also, b) stems contain allelochemicals and are sometimes the principal sources of toxicity, c) leaves are the most important sources of allelochemicals. Specific inhibitors in leaves have been demonstrated by many workers, d) flowers/inflorescence and pollen: although studies on flowers or inflorescence are limited, but the pollen of corn and sunflower inflorescence have allelopathic properties, e) fruits: many are known to contain toxins and have been found inhibitory to microbial growth and seed germination, and f) seeds of many plant families or species have been found to inhibit seed germination and microbial growth.

Origin and nature of allelochemicals

Allelopathic effects of sunflower on crops

According to (Whittaker 1970; Whittaker and Feeny 1971), most allelochemicals are secondary substances which do not occur in all living beings but appear sporadically. These substances are biosynthesized from the metabolism of carbohydrates, fats, and amino acids and arise from acetate or the shikimic acid pathway (Robinson 1963). Many of these compounds have been implicated as allelopathic agents and have been classified into various classes (Horsely 1977; Mandava 1985; Putnam 1985; Rice 1974, 1979). Further these compounds divided into 14 chemical categories: a) cinnamic acid derivatives, b) coumarins, c) simple phenols, benzoic acid derivatives, gallic acid, and protocatechuic acid, d) flavonoids, e) condensed and hydrolysable tannins, f) terpenoids and steroids, g) water soluble organic acids, straight chain alcohols, aliphatic aldehydes, and ketones, h) simple unsaturated lactones, i) long chain fatty acids, j) naphthoquinones, anthroquinones, and complex quinines, k) amino acids and polypeptides, l) alkaloids and cyanohydrins, m) sulfides and mustard oil glycosides, and n) purines and nucleotides (Rice 1974). However, (Putnam 1985, Putnam and Tang 1986) grouped these chemicals into 11 classes: a) toxic gases, b) organic acids and aldehydes, c) aromatic acids, d) simple unsaturated lactones, e) coumarins, f) quinines, g) flavonoids, h) tannins, i) alkaloids, j) terpenoids and steroids, and k) miscellaneous and unknowns. All the naturally occurring compounds of the above categories are not allelochemicals. Derivatives of cinnamic acid, benzoic acid, coumarin, and terpenoids are the commonly reported allelochemicals; however, the terpenoids are the most often reported allelochemicals. The terpenoids are of limited distribution and are produced in small quantities, whereas phenolic compounds (cinnamic acid, benzoic acid, and coumarin) are present in fair abundance (Mandava 1979; Robinson 1967).

Occurrence of allelochemicals These are produced in above or below ground plants parts or in both to cause allelopathic effects in a wide range of

The proceeding sunflower crop decreased the plant length, dry matter, and yield of all subsequent test crops as compared to those sown in fallow plots. The maximum reduction in growth (plant height, dry matter), yield attributes, and grain/fodder yield was observed in cotton and sunflower, a minimum in cereals (sorghum, pearmillet, maize), and moderate in legumes (cluster bean, cow pea, green gram) (Narwal 1994, 1996, 1999). Similar results were obtained by (Bauer 1973) who stated that in a maize/rye rotation, sunflower was sown into the rye stubble and ploughed in at cliff developmental stages with or without additional N and was compared to FYM as well as plots given no fertilizer. When ploughing was delayed until flowering, sunflower reduced the yields of the succeeding crops. Even if ploughed under at an earlier stage, additional N was essential to increase the yield and the response was slight. Sunflower green manure had no measurable effect on soil organic matter content. Caution is recommended with the use of sunflower as green manure, as it is seldom economical and could lead to serious yield losses.

Field/pot culture studies It has been observed that under field conditions sunflowers inhibit the germination and growth of succeeding crops grown in the same plot. Previous study shown that the germination and growth of sesamum grown after the incorporation of sunflower by-product were strongly inhibited and plant population declined by 20%, while reduction was only 13% when sesamum succeeded sunflower (Prusty et al. 1994). The growth of other crops such as pigeon pea, blackgram, greengram, and groundnut was reduced initially. A robust research has been conducted in this direction by several researchers, who explained that sunflower crop left some phytotoxins in the soil, which adversely affected the growth and yield of succeeding mungbean, soybean, cowpea, pigeonpea, sesamum, maize, pearmillet, sorghum, and rice crops. The application of higher doses of urea or

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FYM did not reduce the adverse effect of sunflower on succeeding crop yields (Sandhu 1997; Anjum and Bajwa 2010). The allelopathic compounds released by sunflower in the soil, adversely affect the succeeding crops upto 12 weeks. The phytotoxicity of soil incorporated residues reduced the height and dry matter of pearmillet and soybean upto 120 days. In a greenhouse experiment, (Iron and Burnside 1982) revealed that soybean height and fresh weight were significantly reduced by competition with sunflower, whereas sunflower height was not reduced by any level of competition. Although sunflower fresh weight was reduced by high sunflower and soybean populations, in further studies it was found that 2% (w/w) powder of sunflower leaves, spread on the soil surface, reduced emergence and growth of soybeans, sorghum, and sunflower. A mixed powder from sunflower stems and branches also reduced growth of these three species, but to a lesser extent. Growth of all three species and germination of sunflower were reduced in soil or nutrient soil in which sunflower had been previously grown, suggesting that the phytotoxic root exudates were produced by sunflowers. Studies conducted by (Park et al. 1992) who concluded that radish and Echinochloa colonum germination, root length and fresh weight were adversely affected by various concentrations of acidic and neutral fractions of root exudates from sunflower. Root lengths were inhibited more than shoot lengths; basic and aqueous fractions had no effect on germination. In a similar line, it has been shown that the effect of sunflower on succeeding crops and supported that sunflower infested soil and its amendment with sunflower biomass caused seedling mortality in test crops but the trend differed from germination (Boz 2003; Narwal et al. 1999a). The addition of sunflower roots to infested soil, caused maximum mortality in seedling of test crops, followed by full plant biomass amended infested soil and infested soil alone caused the least mortality. The seedling mortality in test crops followed the order: cowpea > cluster bean > green gram > maize > pearmillet > sorghum. They also determined biomass decomposition of sunflower in the laboratory; CO2 evolution was monitored to determine the pattern and duration of decomposition. The decomposition of soil incorporated shoot of sunflower under laboratory conditions was very fast in the beginning and stabilized 7-8 weeks after start of decomposition. In 9 weeks, 57.1% organic carbon from sunflower shoots was mineralized/decomposed. The germination of sequential ladyfinger crop differed significantly due to weed control treatment in a previous sunflower crop (Nanjappa et al. 1999; Kayode and Ayeni 2009). Mulching of sunflower stalks at 10 t/ha significantly reduced the germination of only lady finger (40%) as compared to other treatments (56 to 60%). While the differences were not significant in other crops due to weed control treatments. Further, the average germination percentage of all test crops was below 60% and peas and finger millet were severely affected (9.78 to 10.67%). Similarly the dry matter production (9.78g/plant) and seedling vigour (0.72) of finger millet and ladyfinger (9.57) were significantly reduced due to sunflower

stalk mulching at 10t/ha in the previous sunflower crop as compared to other weed control treatments (Table 1). This reduction in dry matter production and seedling vigour may be attributed to the allelopathic effect of sunflower crop and the stalks. The adverse effect of sunflower decreased with delay in sowing. It was conspicuous upto 4 weeks after incorporation and thereafter leveled up. The additional application of nitrogen did not overcome the adverse effect of sunflower (Sandhu 1997).

Green manuring Green manuring is a very ancient practice and mainly used to increase the organic carbon and fertility rate of the soil. Generally legume crops are green manured at the knee-high stage, when these are succulent. This topic has been reviewed several times, however, recently there are reports from European countries that green manure of Brassica species provided significant weed control in the crops and minimizes the use of herbicides (Oleszek et al. 1996). The main aim of this research was that allelochemicals present in the plant could be utilized for the control of pests (insects, nematodes, pathogen, weeds) and to minimize the use of pesticides, which cause many environmental problems. The Brassica species contains glucosinolates compounds, which have herbicidal properties. Likewise, there are reports of the use of velvetbean (Mucuna species) as green manure to control the weeds in South American countries. The velvetbean contains the chemicals L. DOPA, which is responsible for weed control. In view of the salient findings of these reports (i.e., use of mustard and velvet bean green manure for successful control of weeds) has initiated number of scientists to explore this new field of research. It has been postulated that sunflower green manure had no measurable effect on soil organic matter content. Caution is recommended with regard to the use of sunflower as green manure as it is seldom economical and could lead to serious yield losses (Bauer 1973). Research findings have concluded that oilseed crop such as sunflower or mustard as green manure led to soil microbial biomass, carbon mineralization, and soil enzyme activity. The results indicate that the green manuring improved the organic matter status of soil and soil microbial activity was vital for the nutrient turnover and long-term productivity of soil (Chander et al. 1997; Singh et al. 2001) (Table 1). Literature pertaining to exhibit that sunflower shoots from o 0 to 120 days old plants were dried at 60 C, ground to pass a 1 mm mesh and incorporated into dry loamy sand at 0, 0.3, 0.4, or 0.5% (w/w) 8 days before sowing Pennisetum glaucum in pots. Seedling growth was promoted by incorporation of sunflower crop residues from the vegetative stage (upto 75 days after sowing), whereas 90 to 120 days old residues inhibited germination and seedling growth (Gill and Sandhu 1996). Studies conducted on sunflower, maize, cotton, pigeonpea, soybean, and pearmillet where seeds of these species were sown in pots containing ground sunflower leaves from a mature crop incorporated into the soil (0.5-2.5% w/w

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basis). Decomposing sunflower leaves, decreased the sunflower seed germination in all other crops. While the shoot and root growth responses to allelopathic effects were dependent on the species, the adverse growth effects on all the species were evident at the higher concentrations (Gill and Sandhu 1993; Kaur et al. 1999) studied that Mungbean (Vigna radiata) cv. K-851 and pearmillet (Pennisetum typhoides, P. glaucum) cv. HHB-67 were germinated on sandy loam soil with 1.5 or 3.0 t ground sunflower residues (stems or leaves) with or without N. The residues initially did not affect germination. However, germination was reduced significantly in the first week, with greater reductions with higher residue rate and with N the germination percentages returning to normal after 2-3 weeks (Table 1). The percent seeds were germinated of P. aureus var.ML-267, C. arietinum var. C-235, Trigonella foenumgraecum var. HFM-65 and P. americanum var. HHB-60 sown in sunflower green manure free soil (control). In contrast, none of the seeds of any of these crops sown in 0.25, 0.5: 1.0 (w/w) manure-soil mixtures germinated upto 20 days (Pariana 1992).

Bioassays A significant literature deals with that growth of sorghum seedlings in nutrient solution was significantly reduced by the addition of the aqueous leaf extracts from sunflower at concentration as low as 1 g fresh weight/120 ml solution. Growth reductions were accompanied by decreases in leaf water potential and increases in diffusive resistance (Table 1). Incorporation of 2 g dried sunflower leaves into 80 g soil significantly reduced the growth of sorghum seedlings for 2 weeks (Schon and Einhellig 1982). Water extract from mature leaves of sunflower at a concentration of 10 mg dry weight/ml showed a slightly reduced seed germination but caused significant reduction in seedling growth of most plants tested. The degree of inhibition on plant growth varied depending on plant species (Tongma et al. 1997). The inhibitory activity of water extract from leaves and stems on the growth of sorghum seedling was similar but higher than the activity of water extract from roots. There was no difference in phytotoxic activity between the extract from green senescent leaves. The water extract applied in soil also inhibited root growth of the plants tested but this inhibitory activity declined in the soil (Zeng et al. 2008). It has been reported that seeds of tomatoes cv. campbell, soybeans cv. vernal, maize hybrid T-66 and Phaseolus vulgaris cv. ICA-Pijao were treated with aqueous extract of root and above ground parts of sunflowers cv. Cabure-15. Aqueous extracts significantly reduced germination rate only in Phaseolus vulgaris. Leaf growth of tomatoes, leaf and root growth of maize, leaf and root length of tomatoes, maize, and P. vulgaris and root biomass of P. vulgaris and maize and total leaf biomass of tomatoes were significantly reduced by sunflower extracts (Beltran et al. 1997). There were no significant effects on the germination and growth of soybeans. In laboratory bioassay, the germination of blackgram and soybean seeds was reduced by the aqueous

extract of sunflower residues. However, stem and leaf extract (1: 15 dilution) of dried sunflower tissues also inhibited the dry weight of 15 days old blackgram and soybean seedlings to the extent of 40-60%. In glass house studies, ground leaves or sunflower chopped shoots when surface applied, inhibited blackgram growth by 25% and soybean by 30%. In pot studies, blackgram and soybean seedling grown with incorporated chopped sunflower residues produced only 50% dry weight than with same amount of residues kept on the soil surface after 35 days sowing. Soil incorporated chopped sunflower residue @ 12g/pot suppressed the weed numbers by 85 and 78% in blackgram and soybean, respectively. The ground leaf material applied on surface at 27g/pot reduced the weed population by 65% compared to residue free treatment (Dharmaraj et al. 1994b). Investigation conducted by (Tongma et al. 1997) and concluded that the aqueous extract of leaves, stems, and roots of Mexican sunflower was inhibitory to seed germination and seedling growth of 17 selected crops and weeds. The aqueous extract from mature leaves at a concentration of 10 mg dry weight/ml showed a slight effect on seed germination but caused significant reduction in seedling growth of most plant tested. It was also stated that the inhibitory activity of aqueous extract from leaves and stems on the growth of sorghum seedling was similar but higher than the aqueous extract of roots.) Significant growth reduction in sorghum seedling was found from additions of sunflower extract at concentration as low as 1 g fresh weight in 120 ml nutrient solution. A reduction in sorghum growth was accompanied by decrease in leaf water potential and increases in diffusive resistance. Incorporation of dried sunflower leaf material into soil in which sorghum seedlings were germinated and growth caused significant depression in growth over a 2 weeks test period with the addition of 2 g residue to 80 g soil (Schon and Einhellig 1982). Studies also indicating that the wheat germination in a soilless medium was not affected by aqueous extract of sunflower residues, however stem and leaf extract (1: 10 dilution) of dried sunflower tissues inhibited dry weight gain of 5 days old wheat seedlings by 20-40%. In green house studies, ground leaves or forage chopped shoots, when surface applied, promoted wheat growth. Wheat tissue had significantly greater N when grown with ground leaf residues. Forty days old wheat grown in pots with incorporated chopped sunflower residue had only one-third the dry weight of plants with the same amount of residue on the soil surface. Chopped sunflower residues equivalent to 6.9 t/ha suppressed weed number by 50% if incorporated, and ground leaf material surface-applied at 15 t/ha reduced weed population by approximately 75% when compared with residue-free treatment. In a split-plot field study, wheat was grown following sunflower or fallow (Table 1). The plot splits were managed as either no tillage (residue no surfaces) or conventionally tilled (residue incorporated). Wheat grain yield were higher in the no tillage treatments (5.2 t/ha) than

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in conventionally tilled treatments (4.9 t/ha) and residue application did not affect grain yield. Overall, the results suggest that sunflower residue can inhibit early weed growth and that incorporation of residues may reduce grain yield, but no tillage production of wheat following sunflower appear viable (Morris and Parrish 1992). Leaf aqueous extract of sunflower was more toxic than root extracts to germination and seedling growth of wheat and sunflower described by (Sandhu 1997) who also suggested that the critical concentration or inhibition threshold beyond which severe growth inhibition occurred was observed to be 50 g -1 L in laboratory experiment and 0.3% (w/w) and above-dried residue under pot culture experiment. In addition to the concentration of the extract/residues, the stage of plant growth played a major role because the allelochemicals from the reproductive phases of sunflower were inhibitory than that from the early vegetative studies. Studies have shown that sunflower var. MSFH-8 exhibit phytotoxicity towards other plants. Phytotoxins/allelochemicals leach from the plant in water-soluble glycosidic forms, hence aqueous leachates exhibit phytotoxicity to other plants. The response varied from plant to plant. Cyamopsis tetragonoloba, Trigonella foenum-graecum, Pennisetum americanum, Lens esculenta and Pisum sativum were resistant indicators towards aqueous leachates of Helianthus annuus, Cosmos bipinnatus, Aster chinensis, Impatiens balsamina and Brassica juncea, var. napus on the other hand, were susceptible to the leachates of sunflower (Pariana 1992).

Allelopathic effect of sunflower on weeds Sunflower is a rich source of sesquiterpenoids and other plant metabolites with a wide spectrum of biological activities and allelopathic to weeds. Subsequent bioassays were conducted with fractions obtained from the first chromatographic separation from the medium polar bioactive fractions (Table 2). Twenty sesquiterpene lactones with gema cronolide and guaianolide skeleton and four members of a new family of sesquiterpene, heliannial in addition to triterpenes, flavonoids coumarins, and lignin were isolated, characterized, and biologically tested as allelochemicals with a potential use as natural herbicides (Macias et al. 1993).

Crop residues, mulches, green manuring In field studies (Francis and Semiday 1992) investigated that surface incorporation of mature sunflower at 32,000 kg/ha (fresh weight) provided 86% reduction in total weed number. Weed species showing susceptibility to mature sunflower included Sida spinosa, Digitaria sanguinalis, and Amaranthus album. It was established that cotton lint yield in non-weeded plots was higher with levels of mature residues of 16,000 and 32,000 kg than with no residues. Immature sunflower residues resulted in lower weed numbers when combined with 0.9 kg/ha fluometuron

pre-emergence than when used alone. S. spinosa, Ipomoea hederacea (Pharbitis hederacea), and Abutilon theophrasti showed susceptibility to residue level than at 0-8,000 kg level of immature sunflowers. In a field experiment, (Iron and Burnside 1982; Khanh et al. 2005) suggested that in competition studies soybean cv. Amsoy 71 was grown with high and low densities of sunflowers with or without hand weeding; it was found that 4-6 weeks free from sunflower were needed for maximum yield. In pot experiments, the decomposed straw of sunflower had an inhibitory effect on the number of sprouting Sorghum halepense plants and bird foot trefoil and inhibited weed mass in these species (Muminovic 1991). Sunflower show depressed height of Avena fatua, Agropyron repens (Elymus repens), Echinochloa crus-galli, Ambrosia artemisiifolia, and Chenopodium album and also depressed the mass of the three last named species. The maximum reduction occurred at 15,000 kg leaf litter of sunflower incorporation (tests were made at 10,000, 15,000, and 20,000 kg); however germination of maize was not affected (Dharmaraj 1998; Xuan et al. 2005). At 15,000 kg leaf litter and dry matter production was inhibited slightly in greengram, completely in soybean and contrarily, stimulated the maize growth. It is suggested that the allelopathic effect of sunflower leaf litter is due to presence of phenolic acids i.e., p-coumaric, vanillic, syringic, p-hydroxy benzoic, and ferulic acid were detected in 2N NaOH hydrolysis (Shiraishi et al. 2005; Uremis 2009). In agronomical studies, practices to overcome the allelopathic effect of sunflower leaf litter on blackgram, soybean, and cotton indicated that the germination and dry matter accumulation was not reduced when sowing of succeeding crops was done 10 weeks after leaf litter incorporation both at 10,000 kg and 20,000 kg when cotton was sown 3-8 weeks after leaf litter incorporation, germination was not reduced and dry matter was increased (Table 2). It has been found that sunflower straw depressed the height of Avena fatua, Agropyron repens, Elymus repens, Echinochloa crus-galli, Ambrosia artemisiifolia, and Chenopodium album and also depressed the mass of the three last named species. Wheat, hemp and pea straw depressed the height of E. repens and rye straw depressed the height of A. artemisiifolia and C. album. Sunflower and rape straw exhibited inhibitory effects on the biomass of A. fatua, whilst hemp straw had a stimulatory effect. Pea straw depressed the mass of S. halepense and E. crus-galli (Muminovic 1991). Parthenium hysterophorus Experiments were conducted to test whether sunflower rhizosphere soil (SRSS) in pot and sunflower green manuring (SGM) in field at various stages i.e., 75, 90,105, and 120 days after sowing (DAS) can reduce Parthenium hysterophorus. Two cover crops, green gram (GG) (Vigna radiata) and pearmillet (PM) (Pennisetum glaucum) were used. Field experiments revealed that all growth and yield attributes of P. hysterophorus were inhibited maximum at 75 DAS of SGM with treatment SGM+PM and the inhibitory

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effect decreased with increase of sunflower stage growing in the field. Pot experiments showed that SRSS at 75 DAS proved maximum inhibitory to growth and yield attributes of P. hysterophorus as compared to higher stages (Rawat et al. 2011, 2012) (Table 2). Similar results found by (Pariana 1992) who revealed that aqueous leachates of sunflower inhibited the chlorophyll content, cell survival, and water content of P. hysterophorus leaves. The combination of leachates and herbicides rapidly decreased the chlorophyll content, water content, and cell survival. The leachates from sunflower tremendously enhanced the activity of herbicides by facilitating the rate of uptake and translocation. The various extract fractions from sunflower leaves retarded the rooting as well germination of Parthenium. The effect was based on the concentration. The unsaponified fraction, derived from petroleum ether fraction effectively reduced the rooting of stem cutting and germination of seeds in Parthenium hysterophorus. Weed control by using aqueous extracts of leaf and stem tissue of Helianthus annuus in combination with a herbicide (EPTCS-Ethyl diprophyl carbamothiate) (Leather 1987). Trianthema portulacastrum Herbicidal resistance in horse purslane (Trianthema portulacastrum) threatens the quality and yield of Kharif crops in India, prompting research to discover novel natural plant compounds with herbicidal properties. Due to its novel nature and potentially interesting chemistry, the American native, sunflower (Helianthus annuus), was tested for its ability to suppress horse purslane growth and its feasibility for use in weed control strategies. Aqueous extract of sunflower significantly inhibited seed germination, seedling growth, and dry matter accumulation of T. portulacastrum in laboratory bioassays at concentrations of 15, 10, and 5%. In pot trials, sunflower rhizosphere soil (SRSS), at the stage of 60 days after sunflower sowing (DAS), inhibited above 50% of growth and yield attributes of T. portulacastrum (Table 2). Extract fractionation showed highest phytotoxicity against test weed shoot and root growth at 100 ppm (Rawat et al. 2013). Experiments were conducted in laboratory, glasshouse, and field studies to determine the phytotoxic effects of sunflower cultivars on the suppression of weed seed germination and growth. Weed population of Trianthema portulacastrum, Parthenium hysterophorus, Flaveria australasica Hook, Portulaca oleracea, and Amaranthus viridis L. were reduced by 91, 84, 83, 95, and 85%, respectively (Dharmaraj et al. 1994b). The weed biomass was reduced by 94, 93, 90, 79, and 92% in Trianthema portulacastrum, P. hysterophorus, L. Flaveria australasica Hook, Portulaca oleracea, and Amaranthus viridis, respectively, under field conditions by the sunflower cv. MSFH-I. In field studies, (Dharmaraj et al. 1994c) investigated the allelopathic potential of sunflower (Helianthus annuus L) varieties. The results showed that both the varieties BSH-I and MSFH-I significantly inhibited the weed population as well as weed biomass of Trianthema portulacastrum L by 96

and 94%, respectively. Laboratory bioassay studies revealed that the ethyl acetate extract of air-dried sunflower leaves significantly reduced the germination of Trianthema portulacastrum by 46% as compared to the control. Allelochemicals leached from sunflower varieties resulted in drastic reduction in the levels of auxin and gibberellin content by 38.7 and 42.4%, while abscisic acid content increased by 1.81 to 2.10 fold from vegetative to flowering and flowering to maturity stage. Trianthema portulacastrum suffered a higher reduction in photosynthetic rate at all stages. The total chlorophyll content was reduced by 15, 17, and 35% in T. portulacastrum L. at the vegetative, flowering, and maturity stages of the sunflower. Soluble N was found to decrease under the influence of sunflower leachates and was particularly increased at the vegetative stage. Relative water content decreased substantially under sunflower leachate treatment (26%) in T. portulacastrum L. on the analysis of the leachate of sunflower, most of the phenolic compounds i.e., p-coumaric, vanillic, syringic, p-hydroxybenzoic, and ferulic acid were detected in 2N NaOH hydrolysates. These results indicate that increased leaching of phenolic compound from the intact roots reduces the weed population and growth. In the sand culture studies in the glass house, leachates of dried sunflower leaf and stem tissue inhibited broad leaved weeds seedling growth but had little effect on the grassy weeds i.e., Cynodon dactylon (L), Dactyloctenium aegyptium (L), Echinochloa colonum (L), and Chloris barbata (L). Germination of Trianthema portulacastrum and P. hysterophorus seeds at 30°C in undiluted aqueous extract of sunflower leaf tissue was inhibited to the extent of 82%, but was stimulated to the extent of 165% at 25 and 50 fold dilutions. Sunflower root exudates inhibited the seedling growth but were less effective than leaf and stem tissue leachates. Germination of weed seed was affected by root exudates over a 3 year period. Weed density and percent ground cover increased less in field plots of sunflower than in control plots. Analysis of the culture solution indicated that level of phenolic acid were too high to cause the observed effects and it is postulated that the final inhibitory effect possibly due to the exudation of P-hydroxy benzoic acid, p-coumaric acid, syringic acid, and vanillic acid and other allelopathic compounds. In the pot experiments (Gimsing and Kirkegaar 2009; Muminovic 1991) reported that the sunflower straw depressed the height of Avena fatua, Agropyron repens (Elymus repens), Echinochloa crus-galli, Ambrosia artemisiifolia, and Chenopodium album and also depressed the mass of the last named species. Sunflower and rape straw exhibited inhibitory effect on the biomass of A. fatua (Table 2).

Bioassays An in-vitro study was conducted to determine the allelopathic potential of sunflower, a potential suppressor of dicotyledonous weeds. Sunflower extracts were prepared using various solvents measuring the seed germination and seedling growth of Trianthema portulacastrum, Parthenium hysteroph-

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orus, and Amaranthus viridis. The presence of inhibitory activity was confirmed by extraction of sunflower plants with 80% ethanol. The extract was fractionated by partitioning the aqueous phase against petroleum ether, chloroform, and ethyl acetate. Bioassay of these fractions revealed the presence of inhibitors of seed germination and seedling growth of Trianthema portulacastrum L. in all the fractions (Table 2). These fractions at a level equivalent to 4 g fresh plant material per Petri dish inhibited the seed germination and seedling to the extent of 56 and 57%, respectively. Chloroform and aqueous fraction inhibited seedling growth by 36 and 37%, respectively, in Amaranthus viridis L. and 40 and 22% in Parthenium hysterophorus. Inhibitory activity was found mainly in chloroform and water-soluble extract of air dried sunflower. When chloroform extract of sunflower shoot was purified by Column Chromatography, inhibition was associated with fraction containing chlorogenic acid (C.G.A.) 3-caffeoyl quinic acid (4 CO) and neo chlorogenic acid (neo CGA). A large increase in the concentration of isomer of chlorogenic acid was observed in extract of sunflower plants. More phenolic compounds were leached from living intact roots, dried leaves, and tops of sunflower plants (Dharmaraj and Sheriff 1994a). Water extracts from leaves and stems of sunflower clearly inhibited the germination of common poppy and common amaranth (Ciarka and Senatorska 2000; Ciarka et al. 2002; Wu et al. 2000). Germination of common amaranth was extremely delayed by both extracts. In barnyard grass seeds, there was no effect or slight stimulation occurred when compared with the control.

Allelochemical in sunflower plant The potential of sunflower as source of allelochemicals is well known (Varela 1982) and bioassays of leaf aqueous extracts show strong inhibition and stimulation in germination and root length of test plant species. The leaf aqueous extracts of sunflower 'SH 222’ were found to obtain five new guananolides and the annuolides possess allelopathic activity of sunflower. All the guainolides possess allelopathic activity over dicotyledon species and are likely to be involved in the allelopathic activity of sunflower cultivars (Macias et al. 1993; Macias et al. 1996a) characterized absolutely new allelochemicals viz., 16 sesquiterpene lactones, five flavonoides, four kaurenoed diterpenes, 14 bisnorsesquiterpenes, and sesquiterpene heliannulos. The heliannuols proved inhibitory to dicot weed species hence, they may be an excellent source as a pre and post-emergence herbicides at very low doses (10-4 to 10-9). In laboratory study an unreleased sunflower hybrid produced allelochemicals shown by GLC and MS to be a similar group of organic compounds to those found in the male parent. They were present in living, senescing, and dried foliage, and their possible relationship with previously identified allelochemicals was discussed (Lovett et al. 1982). Observation were made

that in addition to known phenolic compound in sunflower, they characterized new 16 sesquiterpene lactones (nine glucuanolides and seven germacranolides), five flavonoids, four kaurenoids diterpenes, four bisnoresquiterpenes, and two novel families of sesquiterpenes Heliannuoles (15 compounds) and Heliespinores (four compounds) (Macias et al. 1996a). In earlier studies it was reported that hydroquinone, beta-resorcyclic acid, vanillic acid, caffeic acid, salicyclic acid, and quercetin were characterized from the acidic fraction of root exudates from sunflower. Hydroquinone, gentisic acid, beta-resorcyclic acid, vanillic acid, caffeic acid, ferulic acid, and quercetin were elucidated from the neutral fraction (Park et al. 1992). According to (Ohno et al. 2001) who reported that from the exudates of germinating sunflower seeds they isolated a stereoisomer of diversifolide, 4, 15-dinor-3-hydroxy-1 (5) Xanthene-12, 8-olide (designated sundiver sifolide) as determined by analysis of its IR, APCI, ESI, and HR-MS and 13 C and IH NMR spectra. This substance inhibited shoot and root growth of Cat’s-eye (Veronica persica) by about 50% at a concentration of 30 ppm. It also showed species selective activity on the shoot and root growth of tested plants (lettuce, tomato, Celosia cristata, Digitaria ciliaris, and Echinochloa crus-galli) when Cat’s eye growth was inhibited. Furthermore, it was detected from the extract of river sand where sunflower seeds were incubated (Holethi et al. 2008). These results indicate that sundiver sifolide has an allelopathic function in sunflower plants. Study conducted by (Sandhu 1997) who reported that the chromatographic, physiochemical, and spectral analysis showed the presence of chlorogenic and isochlorogenic acids in sunflower. According to (Pariana 1992), the allelochemicals from sunflower are polar and non-polar in nature. Two terpenoid compounds (A and B) were isolated and characterized from the relatively more allelopathic fractions. Both these compounds (A and B) showed allelopathic activity and inhibited germination parameters viz., photosynthesis and respiration of the target plant. Phaseolus aureus var. ML-267. Compounds A impairs the respiratory machinery of the germinating propagules, their impact depends on the time and concentration. Chemical studies on different parts of Helianthus annuus have led to the identification of a number of compounds; prominent among them being the sesquiterpene lactones. Further, (Spring et al. 1982) isolated two sesquiterpene lactones named niveusin C and 15-hydroxy-3-dehydroxy fruticin from leaves and stems of Helianthus annuus. Both sesquiterpene lactones strongly inhibit, indole-3-acetic acid (IAA) induced elongation growth of Avena sativa L. caleoptile segments and Helianthus annuus L. hypocotyls segments. Further investigations on growth inhibiting substances from young leaves and the apical part of stem of H. annuus resulted in the extraction of three additional sesquiterpene lactones (Spring et al. 1982). In this series of experiments (Spring and Benz 1989) later identified six sesquiterpene lactones by HPLC separations from capitate glandular trichomes of Helianthus annuus L (Table 3).

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Allelochemicals in sunflower plants soil The rhizosphere soil of sunflower also reduced the all parameters namely plant height, population, earhead length, and yield of all test crops and weeds. Test weed Parthenium hysterophorus was found more sensitive to applied soil followed by Trianthema portulacastrum and test crops. The applied soil proved most inhibitory at initial 60 DAS and the effect of inhibition was observed upto 90 DAS of sunflower. After that the rhizosphere soil proved very mild inhibitory to test crops but little inhibitory to test weeds. The harmful effect of such soil might be due to the presence of allelochemicals of sunflower released by roots into the soil (Azania et al 2003; Rawat 2002). The soil of Helianthus annuus is rich in chemicals compared to the soil free from this plant. With increasing distance, the content of chemical gets reduced so that it is almost negligible at a 100 m distance. It was maximum under the aerial canopy of the plant. With depth, the chemical contents showed variation. The mode of release of the chemical could be due to decomposition of fallen leaves or leachates including stem flowers or exudation from roots. Gallic acid, gentistic acid, chlorogenic acid, p-hydroxy benzoic acid, acetic acid, vanillic acid, p-coumaric acid, and ferulic acids are some of the phenolic acids that were released by sunflower into the soil. Their maximum amount was found in a 0-10 cm radius and a decrease with increasing distance from the plant (Pariana 1992). The soil chemicals of sunflower crop inhibited the germination, photosynthesis and respiration and rooting of hypocotyls cutting of the target plant and also exhibit the dose response relationship. The poor performance of succeeding Rabi and Kharif crops in the field of sunflower is not due to a lack of mineral nutrients but due to sunflower plant residues left in the soil and thereby allelopathic property of the soil. The phytotoxins are active even after the death and partial decay of sunflower plants parts in ratio of 0.125: 1 (biomass: soil). Analysis of soil at different intervals after incorporation of various plant parts of sunflower revealed that sunflower roots were the major source of phenolic compounds in the soil and their release continued for 6-7 weeks after the incorporation of the plant parts (Sandhu 1997; Waller and Nowacki 1978) (Table 3).

Persistence of phytotoxicity in soil It has been recommended that growing sunflower on a large scale may not be harmful to the crops provided: a) there is enough fallow periods after the harvest and b) no residue of sunflower were allowed to decompose in the soil (Pariana 1992). The allelopathic compounds released by sunflower in the soil adversely affect the succeeding crops upto 12 weeks. The phytotoxicity of soil incorporated residues the height and dry matter of pearmillet and soybean upto 120 days. Further he also suggested that the adverse effect of sunflower decreased with delay in sowing. It was conspicuous upto 4 weeks after incorporation and thereafter leveled up. The additional application of nitrogen did not overcome the adverse effect of sunflower. Analysis of soil at

different intervals after incorporation of various plant parts of sunflower revealed that sunflower roots were the major source of phenolic compounds in the soil and their release continued for 6-7 weeks after the incorporation of the plants parts (Sandhu 1997) (Table 3). It has been stated that when cotton was sown 3.8 weeks after leaf litter incorporation, germination was not reduced and dry matter was increased (Dharmaraj 1998).

Conclusion Ample information is available and agricultural production needs are causes for exploiting allelopathy to benefit production systems. Current farming is in a transition of reduction of tillage and less chemical use. Reducing tillage restricts weed seeds to poor germination sites and by utilizing natural phytotoxins leaching from plant residues, the germination of seeds and growth of many weeds can be inhibited. There are many crop species known for their allelopathic potential. Herbicides can be used to supplement cover crops in reduced tillage practices. Crop plant breeding for genetic manipulation and allelopathic potential against weeds is believed to solve, in part, weed problems. Use of proper type and amount of crop and weed mulch should be considered for weed management. Residue management, crop rotation, timing of operations, and proper agronomic practices needs to be identified for specific areas of production to make use of allelopathic conditions. Natural plant products may provide clues to new and safe herbicide chemistry. Thus, modifying these natural products could give more active, selective, and persistent herbicides. Promising results have been shown by selecting for allelopathic crops and including them in the rotation. New target sites of action can be exploited for natural phytotoxins. Thus, many of the allelochemicals have potential as herbicides or as templates for new herbicide classes. Allelopathic compounds are metabolites released from plants that might be beneficial or detrimental to the growth of receptor plants. These compounds are involved in the environmental complex of managed or natural ecosystems. Allelopathic compounds have been shown to play important roles in the determination of plant diversity, dominance, succession, and climax of natural vegetation and in the plant productivity of agroecosystems. The overuse of synthetic agrochemicals often causes environmental hazards, an imbalance of soil microorganisms, nutrient deficiency, and change of soil physicochemical properties, resulting in a decrease of crop productivity. The incorporation of allelopathic substances into agricultural management may reduce the use of synthetic herbicides, fungicides, and insecticides and lessen environmental deterioration. Scientists in many different habitats around the world have demonstrated the above examples previously. It is known that most volatile compounds, such as terpenoids, are released from plants in drought areas. In contrast, water-borne phytotoxins, such as

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phenolics, flavonoids, or alkaloids, are released from plants in humid zone areas. Both allelopathy and autointoxication play an important mechanism in regulating plant biodiversity and plant productivity. A unique case study of a pasture-forest intercropping system, which is particularly emphasized here, could be used as a model for forest management. After the deforestation of coniferous or hardwood forests, a pasture grass, kikuyu grass (Pennisetum clandestinum), was transplanted onto the land. The grass was quickly established within 6 months. Significant suppression of weed growth by the kikuyu grass was found; however, the growth of coniferous or hardwood plants was not suppressed but stimulated. This example as well as others described in this text clearly indicates that allelopathy plays a significant role in sustainable agriculture. Nevertheless, room for allelopathic research in the next century is available for biologists, biochemists, biotechnologists, and chemists. Future allelopathic research should focus on the following tasks: (1) a continuous survey of potential allelochemicals from natural vegetation or microorganisms, (2) the establishment of practical ways of using allelochemicals in the field, (3) to understand the mode of action of allelopathic chemicals in receptor organisms, (4) to understand the role of allelopathic chemicals in biodiversity and ecosystem function, (5) to explore advanced biotechnology for allocating allelopathic chemical genes in plants or microorganisms for biological control, and (6) to challenge the natural product chemists to develop a better methodology for isolating allelopathic compounds or their degraded compounds from the environment, particularly the soil environment.

Acknowledgements The authors are grateful to the director of the G. B. Pant National Institute of Himalayan Environment and Sustainable Development, Kosi-Katarmal, Almora for providing facilities and SERB, Department of Science and Technology (DST), and Indian Council of Agricultural Research (ICAR), New Delhi for financial assistance.

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mediated weed control for sustainable agriculture, In: SS Narwal, P Tauro, eds, Allelopathy in Pests Management for Sustainable Agriculture, Scientific Publishers, Jodhpur, India, pp 23-66 Narwal SS. 1997. Allelopathy and its practical use for weed management. Lecture delivered at Expert Consultation Group Meeting on Weed Ecology and Management. Food and Agriculture Organization, Rome, Italy Narwal SS. 1999. Allelopathy update: basic and applied aspects. Science publishers Inc. Enfield, pp 335-348 Ohno S, Tomita-Yokotani K, Kosemura S, Node M, Suzuki T, Amano M, Yusui K, Goto T, Yamamura S, Hasegawa K. 2001. A species-selective allelopathic substances from germinating sunflower (Helianthus annuus) seeds. Phytochemistry 56: 577-581 Oleszek W, Ascard J, Johansson H. 1996. Brassica as alternative plants for weed control in sustainable agriculture, In: SS Narwal, P Tauro, eds, Allelopathy in Pest Management for Sustainable Agriculture, Scientific Publishers, Jodhpur, India, pp 3-22 Pariana 1992. Allelopathic Properties of Sunflower. Ph.D. Thesis. Department of Botany, Punjab University, Chandigarh, India Park KH, Moody K, Kim SC, Kim KU. 1992. Allelopathic activity and determination of allelochemicals from sunflower (Helianthus annuus L.) root exudates. II. Elucidation of allelochemicals from sunflower root exudates. Korean J. Weed Sci. 12: 173-182 Patrick ZA, Koch LW. 1958. Inhibition of respiration, germination and growth by substances arising during decomposition of certain plant residues in the soil. Can. J. Bot. 36: 621-647 Patrick ZA, Toussoun TA, Koch LW. 1964. Effect of crop residue decomposition products on plants roots. Ann. Rev. Phytopathology 2: 267-292 Prusty ZC, Mohanty SK, Behera B. 1994. Allelopathic impact of sunflower (Helianthus annuus) on the growth of succeeding crops and associated weeds, In: SS Narwal, GS Dhaliwal, Jai Prakash, eds, International Symposium on Allelopathy in Sustainable Agriculture, Forestry and Environment Abstracts Ist, Indian Society of Allelopathy, Haryana Agriculture University, Hisar, India, pp 39 Purvis CE, Jones GPD. 1990. Differential response of wheat to retained crop stubbles, other factors influencing allelopathic potential; intraspecific variation, soil type and stubble quality (Triticum aestivum). Aust. J. Agri. Res. 41: 243-251 Putnam AR, Tang CS. 1986. Allelopathy: State of the science, In: AR Putnam, CS Tang, eds, The Science of Allelopathy, John Wiley & Sons Inc., New York, pp 1-19 Putnam AR. 1985. Weed allelopathy, In: MA Altieri, M Liebman, eds, Weed Physiology, Reproduction and Ecophysiology, CRC Press Inc., Boca Raton, FL, USA, pp 77-88 Rawat LS, Maikhuri RK, Negi VS. 2013. Inhibitory effect of leachate from Helianthus annuus on germination and growth of kharif crops and weeds. Acta Ecol. Sin. 33: 245-252

Rawat LS, Narwal SS, Kadian HS, Negi VS. 2011. Allelopathic effect of sunflower (Helianthus annuus) on germination and growth of Parthenium hysterophorus. Allelopathy J. 27(2): 225-236 Rawat LS, Narwal SS, Maikhuri RK, Negi VS, Pharswan DS. 2012. Allelopathic effects of sunflower on seed germination and seedling growth of Trianthema portulacastrum. Allelopathy J. 30(1): 11-22 Rawat LS. 2002. Herbicidal Potential of Sunflower. Ph.D. Thesis, Department of Botany, H.N.B. Garhwal University Srinagar Garhwal, Uttaranchal, India, pp 219 Rice EL. 1974. Allelopathy. Academic Press, New York Rice EL. 1979. Allelopathy, An update. Botanical Review 45: 105-109 Robinson T. 1963. The Organic Constituents of Higher Plants. Burgess, Minneapolis, Minnesota, USA, pp 306 Robinson T. 1967. The Organic Constituents of Higher Plants. Burgess, Minneapolis, Minnesota, USA, pp 319 Sandhu KS. 1997. Allelopathy Interactions of Crops. Final Technical Report, US-India Fund Project. Department of Agronomy, Punjab Agriculture University, Ludhiana, India, pp 118 Schon MK, Einhellig FA. 1982. Allelopathic effects of cultivated sunflower on grain Sorghum. Bot. Gazette 143: 505-510 Shibaoka H, Mitsuhashi M, Shimokoriyama M. 1967. Promotion of adventitious roots formation by heliangine and its removal by cysteine. Plant Cell Physiol. 8: 161-170 Shiraishi S, Watanabe I, Kuno K, Fujii Y. 2005. Evaluation of the allelopathic activity of five Oxalidaceae cover plants and the demonstration of potent weed suppression by Oxalis species. Weed Biol. Manag. 5: 128-136 Singh H. 2002. Studies to Determine the Weed Management Potential of Sunflower for Sustainable Agriculture. Ph.D. Thesis, Department of Agronomy, CCS University, Meerut, Uttar Pradesh, India, pp 384 Singh HP, Kohli RK, Batish DR. 2001. Allelopathy in agroecosystems: An overview. J. Crop Prod. 4: 1-41 Spring O, Albert K, Hagar A. 1982. Three biologically active Heliangolides from (Helianthus annuus). Phytochemistry 21: 2551-2553 Spring O, Benz, T. 1989. Sesquiterpene lactones of the capitates glandular trichomes of Helianthus annuus. Phytochemistry 28: 745-749 Taylor HF, Burden RS. 1970. Identification of plant growth inhabitores produced by photolysis of violaxantin. Phytochemistry 9: 2217-2223 Tongma S, Kobayashi K, Usiu K. 1998. Allelopathic activity of Mexican sunflower (Tithonia diversifolia) in soil. Weed Sci. 46: 432-437 Tongma S, Kobayshi K, Usui K. 1997. Effect of water extract from Mexican sunflower [Tithonia diversifolia (Hems) A. Gray] on germination and growth of tested plants. J. Weed Sci. Technol. 42: 373-378 Uremis I, Ahmet M, Uludag A, Sangun M. 2009. Allelopathic potentials of residues of 6 brassica species on johnsongrass

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(Sorghum halepense) African J. Biotech. 8: 3497-3501 Varela RM. 1982. Allelopathic Studies on Cultivars of Sunflower. M.Sc. Thesis. University of Cadiz, Puerto Real, Spain Waller GR, Dermer OC. 1981. Enzymology of alkaloid metabolism in plants and microorganisms. The Biochemistry of Plants 7: 317-402 Waller GR, Nowacki EK. 1978. The role of alkaloids in plants, In: GR Waller, EK Nowacki, eds, Alkaloid Biology and Metabolism in Plants, Plenum Press, New York, pp 143-181 Wang TSC, Yang TK, Chuang TT. 1967b. Soil phenolic acids as plant growth inhibitors. Soil Sci. 103: 239-246 Whittaker RH Feeny PP. 1971. Allelochemics: Chemical interactions between species. Science 171: 757-770 Whittaker RH. 1970. The biochemical ecology of higher plants, In: E Sondheimer, JB Simeon, eds, Chem. Ecol. Academic Press, New York, pp 43-70 Wilson RE, Rice EL. 1968. Allelopathy as expressed by Helianthus annuus and its role in old field succession. Bulletin of the Torrey Botanical Club 95: 432-448 Wu H, Pratley J, Lemerle D, Haig T. 2000. Laboratory screening for allelopathic potential of wheat (Triticum aestivum) accessions against annual ryegrass (Lolium rigidum). Aust. J. Agri. Res. 51: 259-266 Xuan TD, Shinkichia T, Khanhb TD, Min CI. 2005. Biological control of weeds and plant pathogens in paddy rice by exploiting plant allelopathy: an overview. Crop Prot. 24: 197-206 Zeng RS, Mallik AU, Luo SM. 2008. Allelopathy in Sustainable Agriculture and Forestry, Springer Science+Business Media, LLC, New York, NY

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Table1. Allelopathic effects of sunflower (Helianthus annuus L.) crop residues, extracts and leachates on germination, growth and yield of test crops in field studies and bioassays. Sunflower residues/ extracts/ leachates

Recipient species

Nature of inhibitory/stimulatory effects

References

Field studies Crop residues

Sorghum, pearlmillet, maize, clusterbean, cowpea, greengram

Reduced plant growth and yield

Narwal et al. 1999a

Crop residues

Mungbean, sesame, maize, pearlmillet, sorghum, rice

Reduced plant growth and yield

Dharmraj 1998

Crop residues

Sesame

Decreased plant population

Prusty et al. 1994

Crop residues

Cucumber, leady finger

Reduced plant growth, development

Nanjapa et al. 1999

Crop residues

Potato

Toxic

Putnam and Tang 1986

Crop residues

Wheat

Inhibited germination, development

Purvis and Jones 1990

Crop residues

Wheat

Reduced growth and yield

Cernusko and Borkey 1992

Pot studies Leaves+shoots

Blackgram, soybean

Reduced drymatter

Dharmraj et al. 1994b

Sunflower leaves

Soybean, sorghum, sunflower

Reduced growth

Irons and Burnside 1982

Crop biomass

Pennisetum glaucum

Promoted seedling growth (early stage)

Gill and Sandhu 1996

Crop residues

Mungbean, pearlmillet

Reduced growth

Kulvinder et al. 1999

Crop biomass

Pennisetum glaucum

Inhibited germination, seedling growth

Gill and Sandhu 1996

Crop leaves

Maize, cotton, pigeonpea, soybean, pearlmillet

Germination, seedling growth

Gill and Sandhu 1993

Sunflower leaves

Sorghum

Reduced growth

Kulvinder et al. 1999

Sunflower infested soil

Cowpea, clusterbean, greengram, maize, pearlmillet, sorghum

Seedling mortality

Narwal et al. 1999b

Bioassays Biomass

Sorghum, maize, soybean, cotton

Seedling growth, drymatter

Narwal et al. 1999b

Root exudates

Radish, Echinochloa colonum

Reduced germination, root length, dry weight

Park et al. 1992

Shoot, root extract

17 selected crops and weeds

Inhibited germination, seedling growth

Tongma et al. 1998

Shoot extracts

Sorghum

Inhibited growth

Tongma et al. 1998

Aqueous extracts

Sorghum

Inhibited seedling growth

Schon and Einhelling 1982

Aqueous extracts

Sorghum, maize

Reduced shoot length, drymatter

Narwal et al. 1999a

Aqueous extracts

Maize

Stimulated germination, development

Narwal et al. 1999a

Shoot root extracts

Maize, tomato, mungbean

Inhibited germination, seedling growth

Beltran et al. 1997

Aqueous extracts

Blackgram, soybean

Reduced seedling growth, drymatter

Dharmraj et al. 1994b

Shoot extracts

Wheat

Reduced seedling growth

Morish and Parish 1992

Soil extracts

Phaseolus aureus

Reduced germination (respiration, photosynthesis)

Pariana 1992

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Table 2. Allelopathic effects of sunflower (Helianthus annuus L.)on weeds. Sunflower residues/ extracts/ leachates

Recipient species

Nature of inhibitory/stimulatory effects

References

Field studies Aqueous extracts

Wheat, sunflower

Inhibited germination, seedling growth

Sandhu 1997

Crop residues

Flaveria australasica, Parthenium hysterophorus, Amaranthus viridis, Trainthema portulacastrum and Portulaca oleracea

Weed population, biomass

Dharmraj and Sheriff 1994a

Pot studies Crop residues

Sida spinosa, Digitaria snguinalis and Amaranthus albus

Reduced weed population

Frans and Semidey 1992

Crop residues

Dicot weeds

Reduced weed population

Anaya 1989; Fleck and Vidal 1993

Decomposed straw

Avena fatua, Agropyron repens (Elymus repens), Echinochloa crusgalli, Ambrosia artemisiifolia and Chenopodium album

Reduced hight, weed biomass

Muminovic 1991

Rhizosphere soil

Parthenium hysterophorus, Trianthema portulacastrum

Reduced seedling growth, yield

Rawat 2002; Singh 2002 Rawat et al. 2012; 2013

Bioassays Stem, leaves extracts

Cynodon dactylon, Dactyloctium ageptium L, Ritcher, Echinochloa colonum L, Chloris barbara

Reduced seedling growth

Dharmraj and Sheriff 1994a

Plant aqueous extracts

Parthenium hysterophorus, Trianthema portulacastrum, Amaranthus viridis

Inhibited germination, seedling growth

Dharmraj 1994c Rawat et al. 2012; 2013

Plant aqueous extracts

Rhumex dentalis, Chenopodium album, Coronopus didynus, Fumeria parviflora

Reduced fresh dry weight

Cheema et al. 1997

Plant aqueous extracts

Parthenium hysterophorus, Trianthema portulacastrum

Inhibeted germination, seedling growth

Rawat, 2002; Singh 2002

Plant aqueous leachates

Parthenium hysterophorus

Inhibited cholrophyll content, cell survival, water content

Pariana 1992

Plant leachates

Trianthema portulacastrum

Stimulated abscisic acid, reduced auxin, gibberllin, total chlorophyll content

Pariana 1992

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Table 3. Allelochemicals isolated from Helianthus genus and their biological activity. Chemical category

Comound

Biological activity

Receiver plant

References

ά-Piene

Inhibited germination and growth

Letuce, onion, tomato

(Macias et al. 1996)

 -Piene

Inhibited germination and growth

Lettuce

(Macias et al. 1996)

Terpinoids Monoterpenes

Bisnorsesquiterpenes

Sesquiterpenes (non-lectones)

Sesquiterpenes (lectones)

Camphene

Inhibited germination

Lettuce

(Macias et al. 1996)

ά-Phelladrene

Inhibited germination

Lettuce

(Macias et al. 1996)

ά-Terpinene

Inhibited germination

Lettuce

(Macias et al. 1996)

ρ-Cimpene

Inhibited germination

Lettuce

(Macias et al. 1996)

Bormeol

Inhibited germination and growth

Lettuce

(Macias et al. 1996)

Terpin-4-ol

Inhibited germination

Lettuce

(Macias et al. 1996)

Dehydrovomifoliol

Stimulated root growth

Onion

Macias et al. 1999

Helinorbisabone

Stimulated root and shoot growth

Barley

Macias et al. 1999

Annuinonnes A

Inhibited germianation

Lettuce

Macias et al. 1996b Macias et al. 1996b

Annuinonnes B

Inhibited germination

Onion

Annuinonnes C

Stimulated root growth

Barley

Annuinonnes D

Inhibited germination

Lettuce

Macias et al. 1999

9-hydroxy-4megatigmen-3-one

Inhibited germination

Lettuce

Herz and Bruno et al. 1986

5,6-epoxy-3-hydroxy- ά-ionone

Inhibited root growth

Wheat

Taylor and Burden. 1970

Heliannuols A, C, H

Inhibited germination

Lettuce

Macias et al. 1999

Heliannuols B,D

Inhibited root and shoot growth

Onion

Macias et al. 1998

Heliespirone

Moderate stimulation in growth

Lettuce, onion

Macias et al. 1998

Heliangine

Stimulated root formation

Greengram

Shibaoka et al. 1967

Inhibited root formation

Oats

Annuolides A-E

Inhibited germination, root and shoot length

Lettuce Barley

Macias et al. 1993

Annuolides F

Stimulated germination, inhibited root and shoot growth

Lettuce

Macias et al. 1996 a

Annuolides G

Inhibited shoot growth

Lettuce, tomato

Macias et al. 1996 a

Helivypolides A, B

Inhibited root and shoot growth

Lettuce, tomato

Macias et al. 1996 a

Helivypolides D, E

Inhibited germination, root and shoot growth

Lettuce

Macias et al. 1994

Lupeol

Moderated inhibition in germination

Lettuce

Macias et al. 1994

Flavonoids

Heliannones A,B,C

Inhibited germination and shoot growth

Tomato, barley

Macias et al. 1997

Organic acids

Citric, malic, succinic, fumaric, malonic and tartaric acids

Autotoxicity, inhibited germination

Sugarcane, rice, wheat, barley etc

Putnam and Tang (1986) ; Evenari 1949

Triterpenes

Fenolics