NewForests 4: 0 1991 Kluwer

281-289, Academic

1991. Publishers.

Printed

in the Netherlands.

Effect of cutting position on rooting and shoot growth of two poplar clones

W. R. SCHROEDER

and D. S. WALKER

Prairie Indian

Administration, SOG 2K0,

Farm Head,

Rehabilitation Saskatchewan,

Shelterbelt Canada

Received 11 December 1989; accepted 18 February

Key

words:

Populus,

hardwood

Centre,

Agriculture

Canada,

1991

cuttings, vegetative propagation,

shoot location

One-year-old shoots from stooling beds of Populus X deltoides ‘Walker’ and ‘Northwest’ were collected in late fall to determine the effect of cutting position on rooting and growth of hardwood poplar cuttings. Cuttings with a minimum diameter of 9.0 mm were obtained from basal, middle and distal locations on the poplar shoot. Rooting and shoot growth were assessed in the greenhouse and under field conditions. ‘Walker’ poplar cuttings collected from basal portions of the shoot and planted in the field had 87.6% rooting and 103.8 cm growth compared to 78.8% and 103.4 cm and 67.6% and 88.8 cm for middle and distal locations respectively. For ‘Northwest’ rooting and growth under field conditions was 84.4% and 94.7 cm for basal, 78.4% and 90.5 cm for mid and 64.4% and 84.3 cm for distal locations. Rooting in the greenhouse was superior to the field. ‘Walker’ cuttings had fewer roots and buds per cutting than ‘Northwest’, however, growth of ‘Walker’ in the field was superior. Abstract. Populus

jackii

Application. For optimum rooting of poplars only the highest quality cuttings should be used. Cutting quality and rootability are dependent on a number of factors including position of cutting on the parent shoot. Using cuttings from basal and mid shoot locations would significantly increase the rooted cutting production of some poplar clones.

Introduction Most Populus deltoides Bartr. and P. balsamijka L. hybrids are readily propagated from hardwood cuttings @ickmann and Stuart 1983). Rooting of cuttings is dependent on several factors including cutting diameter (Bowersox 1970; Dickman et al. 1980) storage temperature (Phipps and Netzer 1981; Cram and Lindquist 1982) fnngal disease (Ostry and McNabb 1982) stooling bed vigor (FAO 1958) and pre-planting treatments (Petersen and Phipps 1976; Phipps et al. 1983). The importance of cutting position on rooting has been reported by several researchers (Bloomberg 1959, 1964; Smith and Wareing 1972a, 1972b; Ying and

282 Bagley 1976; Hansen and Tolsted 1981, and Fege and Brown 1984). Smith and Wareing (1972a) suggested that Populus X robustu cuttings obtained from apical portions of the whip have fewer preformed root primordia. In addition, Smith and Wareing (1972b) hypothesized that poor rooting of cuttings from the apical portions may be related to bud development and hormonal levels. According to Fege and Brown (1984) concentrations of sugars and starch are higher in apical portions of the shoot but the total quantities of carbohydrates were greater in basal fractions due to the greater dry weight of those fractions. The objective of our study was to obtain information on the rooting characteristics of two hybrid poplars P. jackii ‘Northwest’ and P. X deltoides ‘Walker’, specifically, root formation and shoot growth in relation to region of parent shoot.

Methods Entire one-year-old shoots of hybrid Populus clones ‘Walker’ and ‘Northwest’ were collected in November 1986 from clonal stooling beds at the Prairie Farm Rehabilitation Administration (PFRA) Shelterbelt Centre, Indian Head, Saskatchewan. The stooling beds, established in 1983, had been harvested annually for production of hardwood cuttings since 1984. A total of 1350 cuttings each were obtained from basal, middle and distal portions of trimmed shoots from each of the two clones. Mean diameter of ‘Walker’ cuttings from all positions was 10.5 mm and ranged from 9.0 to 11.4 mm, whereas, ‘Northwest’ was 11.5 mm and ranged from 10.0 mm to 11.9 mm. The cuttings were placed in polyethylene bags and stored at - 1 ’ C until further evaluation or planting. Laboratory

study

To determine the number of roots on cuttings from the three shoot locations and two clones, cuttings were placed in 2 L glass containers filled with distilled water. Containers were covered with opaque paper and placed on a laboratory bench at room temperature (2 “C). Water was changed every three days. After 15 days the cuttings were removed and the number of roots per cutting were counted. To evaluate bud development, 100 cuttings from each clone were randomly selected for each shoot location and the number of buds recorded. Greenhouse study The greenhouse

study tested the effects of cutting position

and clone on

283 rooting and growth of the hardwood cuttings. Boxes 45 cm long x 15 cm wide x 15 cm deep were used in the study. Soil from a nursery field was air-dried and sieved through a 6 mm screen. Twelve kg of soil was placed in each box and watered to field capacity. Greenhouse conditions were 16 h of daylight, mean day-night temperatures of 28 and 15 ‘C, respectively, and mean soil temperature fluctuating diurnally between 30 and 20 “C. The study was arranged in split-plot design with five replications. Each main plot (clones) box was divided into three subplot compartments (cutting position). Ten cuttings were placed in each subplot (30 cuttings per box). The 15 cm long cuttings were pushed into the soil with the top of each cutting flush with the soil surface. Afterwards, perlite was sprinkled on the soil surface to minimize evaporation. Soil moisture was maintained at 80% of field capacity by weighing the boxes and adding the appropriate amount of water by hand. Shoot emergence was recorded every three days over a period of 30 days after which the number of cuttings rooted and height of rooted cuttings were obtained. Rate of emergence was determined using the formula described by Bartlett (1937):

R -

i Xi i=l x, * II

Where: R = Emergence rate n = Number of recording periods i = Any given recording period x = Number of emerged shoots Field study The same clone and cutting position treatments as in the greenhouse study were evaluated in the field during the summer of 1987. The field was located at the PFRA Shelterbelt Centre. The soil was classified as an Oxbow clay loam. Prior to planting, the site was rototilled to a depth of 25 cm. A total of 1,000 cuttings of each clone and cutting position were planted in a five replicate split-plot design with two main plot (clones) and five subplot (cutting position) treatments. Each main plot treatment was divided into three subplot compartments. Two hundred cuttings were included in each subplot. The cuttings were planted with a mechanical planter described by Cram (1969). After planting, the soil was sprayed with chloroxuron

284 herbicide (5.5 kg/ha a.i.) and immediately irrigated. Overhead irrigation was applied periodically during the growing season. Shoot emergence was recorded every four days over a period of 28 days. As in the greenhouse study, rate of emergence was calculated. At the end of the growing season, total height of each rooted cutting was recorded. Each subplot was excavated and the percentage of cuttings that rooted was calculated. Statistical analysis The effects of main plots, subplots and interactions between clone and cutting position for both the greenhouse and field studies were tested by ANOVA. Significant differences were tested with Least Significant Difference (LSD) test at the five percent level. Only those results with significance P < 0.5 will be discussed. Results and discussion The number of roots per cutting were related to the location of the shoot from which the cuttings originated for both ‘Walker’ and ‘Northwest’ clones. (Fig. la). The number of roots decreased acropetally for ‘Walker’, whereas, the mid location had the highest number of roots for ‘Northwest’. Smith and Wareing (1972b) reported that the number of preformed roots in Populus X robusta shoots was lowest in distal portions of the shoot. In their study, primordia were not found closer than 17 to 30 cm from the shoot apex. Our laboratory study suggested that root distribution of ‘Walker’ poplar shoots was similar to the P. x robusta in Smith and Wareing’s (1972b) study. Root growth on basal and distal portions of ‘Northwest’ was similar, whereas, cuttings from mid locations had the highest number of roots. The number of buds per cutting varied according to stem position and clone for both the ‘Walker’ and ‘Northwest’ clones (Figure lb). Basal cuttings from ‘Walker’ shoots had a greater number of buds than mid or distal cuttings, whereas, for ‘Northwest’ basal and mid cuttings had more buds than cuttings from distal locations. Smith and Wareing (1972b) postulated that bud development was related to root initiation in poplar cuttings. The results for ‘Walker’ cuttings indicated that bud development was related to root growth. The trends for ‘Northwest’ were not as clear as basal and mid cuttings and similar bud development, however, root growth was much lower for basal than for mid cuttings. The data obtained in the study did not explain the differences between the two clones. Shoots of ‘Northwest’ cuttings from mid locations emerged faster in the

285 II Walker 653 Northwest

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tat

Fig. I. The number of roots (a) and buds (b) per cutting for Walker’ and ‘Northwest’ poplar cuttings obtained from three shoot positions. Least significant differences (LSD, 0.05) are shown for (a) cutting position subplots within clone main plots and (b) for clones within each cutting position.

greenhouse than did those cuttings originating from basal or distal locations (Fig. 2). The superior emergence rate of the mid location cuttings can be explained by the greater number of roots and buds for this location as determined in the laboratory portion of the study. Emergence rate of ‘Walker’ cuttings could not be explained by root growth or number of buds. Possibly, the ‘Walker’ cuttings had buds nearer the soil surface than did the ‘Northwest’ which would result in earlier recorded emergence. In the field study, rate of emergence decreased acropetally for ‘Walker’ and ‘Northwest’ clones (Figure 3a). Cuttings originating from distal locations were slower emerging than those from mid or basal locations. Rate of emergence was similar for both clones when planted in the field. Emergence was faster and less variable in the field than in the greenhouse. This is difficult to explain as growing conditions were superior in the

286 T : G

1000 . 900~-

ifi f P

600

i

700

Id % 3

OWolker 6X4 Northwest

LSD a b 104 79

600

cz 500

Basal

Mid

Distal

Fig 2. Rate of emergence for ‘Walker’ and ‘Northwest’ poplar cuttings obtained from three shoot locations. Least significant differences (LSD, p = 0.05) within (a) clone main plots and (b) for clones within each cutting position.

greenhouse and cutting characteristics of each clone used in both studies were similar. It is possible that conditions may have been too wet in the greenhouse for good root development after initiation. The percent of cuttings that rooted in the greenhouse was excellent regardless of clone or origin of the cutting. In the field study, cuttings originating from basal locations of both ‘Walker’ and ‘Northwest’ had greater rooting percentages than cuttings from mid or distal locations, however, only differences between basal and distal locations were significant (Fig. 3b). Hansen and Tolsted (1981) reported that position had a greater effect on rooting of poplar than cutting diameter. In their study, basal cuttings generally had greater rooting even if diameters were small. In our study, position was assumed to be the predominant factor affecting rooting as cutting diameter of basal, mid and distal cuttings was similar. Rooting of ‘Walker’ and ‘Northwest’ clones was similar. Height of rooted cuttings was not affected by clone or cutting position in the greenhouse study. In the field study, basal and mid cuttings for ‘Walker’ had 17% more height growth when compared to distal cuttings (Fig. 3~). Although not statistically significant, using basal or mid cuttings for ‘Northwest’ increased height growth by 12% and 7%, respectively when compared to distal cuttings. The more rapid growth rate, characteristic of the ‘Walker’ clone (Lindquist et al. 1977) was evident in this study as height of ‘Walker’ after one growing season was greater than ‘Northwest’. Cuttings originating from all positions rooted better in the greenhouse study than in the field study. Conditions for rooting were superior in the greenhouse when compared to the field. In the greenhouse, moisture,

287 LSD Ooo t 900

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--

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U Walker ISY Northwest *,

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60-40-zo-0-t LSD ab

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70 60 50

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Fig. 3. Rate of emergence (a), percent cuttings rooted (b) and rooted cutting height (c) for ‘Walker’ and ‘Northwest’ poplar cuttings obtained from three shoot positions. Least significant differences (LSD, p - 0.05) are shown for (a) cutting position subplots within clone main plots and (b) for clones within each cutting position.

temperature, wind and humidity were near optimum levels for the duration of the study. In the field it was not possible to control environmental factors and moisture to the same extent as in the greenhouse. This would explain the differences in rooting success in the two studies.

288 Growth rate and rooting in the field was highest for cuttings originating from basal and mid locations. However, height of rooted cuttings originating from distal locations was not reduced to the extent where the field outplanting of the rooted cuttings would be affected. All cuttings that rooted were greater than 80 cm in height regardless of the cutting origin. There was, however, a significant advantage in using cuttings from basal and mid locations when rooting was considered. Similarly, shoots of cuttings from basal and mid locations emerged earlier than distal cuttings. The earlier emergence and, in all likelihood, earlier rooting of the cuttings probably had a beneficial effect on cutting performance. In summary, cuttings originating from basal and mid positions provided the highest percentage of rooted cuttings for ‘Walker’ and ‘Northwest’ clones and are the preferred choice of field production of these clones. Rooting and growth of distal position cuttings, although inferior to basal and mid locations were, according to most nursery standards, acceptable. The high rooting percentage of cuttings reported in this study indicates that ‘Walker’ and ‘Northwest’ poplar have excellent rooting ability.

References Bartlett, N. S. 1937. Some samples of statistical methods of research in agriculture and applied biology. Roy. Stat. Sot. Supp. 4: 137-140. Bloomberg, W. J. 1959. Root formation of black cottonwood in relation to region of parent shoot. For. Chron. 35: 13-l 7. Bloomberg, W. J. 1963. The significance of initial adventitious roots in poplar cuttings and the effect of certain factors on their development. For. Chron. 39: 279-289. Bowersox, T. W. 1970. Influence of cutting size on juvenile growth and survival of hybrid poplar clone NE-388. Tree Planter’s Notes 21(4): 1-3. Cram, W. H. 1969. A new hardwoods cutting planter. Tree Planter’s Notes 19(4): 24. Cram, W. H. and C. H. Lindquist 1982. Refrigerated storage of hardwood cuttings of willow and poplar. Tree Planter’s Notes 33(4): 3-5. Dickman, H. Phipps and D. Netzer 1980. Cutting diameter influences early survival and growth of several Populus clones. USDA For. Serv. Res. Note NC-261.4~. Dickman, D. I. and K. W. Stuart 1983. The Culture of Poplars in Eastern North America. Michigan State Univ. East Lansing, Mich. 168 p. Food and Agriculture Organization of United Nations 1958. Poplars in Forestry and Land Use. FAO Forestry and Forest Products Studies No. 12.511 p. Fege, A. S. and G. N. Brown 1984. Carbohydrate distribution in dormant Populus shoots and hardwood cuttings. Forest Sci. 30(4): 999-1010. Hansen, E. A. and D. N. Tolsted. 1981. Effect of cutting diameter and stem or branch position on establishment of a difficult-to-root clone of a Popuhs alba hybrid. Can. J. For. Res. 11: 723-727. Lindquist, C. H., Cram, W. H. and J. A. G. Howe 1977. Walker poplar. Can. J. Plant Sci. 57: 1019. Ostry, M. E. and H. S. McNabb, Jr. 1982. Preventing blackstem damage to Populus

289 hardwood cuttings. pp. 36-43. In Proceedings North American Poplar Council Annual Meeting, Rhineland, WI. Peterson, L. A. and H. M. Phipps 1976. Water soaking pretreatment improves rooting and early survival of hardwood cuttings of some Populus clones. Tree Planter’s Notes 27(l): 12-22. Phipps, H. M. and D. A. Netzer 1981. The inthrence of collection time and storage temperature on Populus hardwood cutting development. Tree Planter’s Notes 32(4): 33-36. Phipps, H. M. Hansen, E. A. and A. S. Fege 1983. Preplant soaking of dormant Populus hardwood cuttings. USDA Forest Serv. Res. Rep. NC-241,8p. Smith, N. G. and P. F. Wareing 1972a. The distribution of latent root primordia in stems of Popuh robusta and factors affecting the emergence of preformed roots from cuttings. Forestry 45: 197-209. Smith, N. G. and P. F. Wareing 1972b. Rooting of hardwood cuttings in relation to bud dormancy and the auxin content of excised stems. New Phytol. 71: 63-80. Ying, C. C. and W. T. Bagley 1977. Variation in rooting capability of Populus deltoides. Silvae Genetica 26: 204-207.