The authors acknowledge financial assistance provided

1979 they became heavily infected with M. terict-poputine. The same clones growing in Palmerston North were free from M. larici-populina although infected with M. medusae. Adjacent susceptible clones such as P. nigra 'Italica' were heavily infected with M. larici-populina. Identification of the rusts from both localities as M. terici-poputine was confirmed by Mrs Gillian Laundon, mycologist at the Plant Health and Diagnostic Station, Ministry of Agriculture and Fisheries, Levin. Pathogenicity of rust collected from the hybrids in Whangarei was compared with that of rust from P. migra and P. x euramericana '1-78' grown in Palmerston North by inoculating a range of poplar clones. Leaf discs, 2 cm diam, were inoculated by first spraying with distilled water, then painting on a suspension of uredospores in distilled water using a fine brush, the spores being applied to the abaxial surface. The use of spore suspensions rather than dry spores for inoculum reduced the risk of aerial con-

by the Australian Wheat Industry Research Council.

REFERENCES (1)

Darlington, L C" and Mathre, D, E. (1976) - Resistance of male sterile wheat to ergot as related to rollination and host genotype, Crop Science 16: 728-730,

(2)

Dillon-Weston, W, A. R" and Taylor, R. E, (1942) - Observations of ergot in cereal crops, Journal of Agricultural Science 32: 457-464,

(3)

Platfor d. R, G" and Bernier, C, C, (1976) - Reaction of cultivated cereals to C/aviceps purpuree. Canadian Journal of Plant Science 36: 57-58,

(4)

Willis, S, S, (1953) - Ergot in wheat variety trials in Herttordshire Plant Pathology 2: 34-35,

New Poplar Clones Help Distinguish Races of Melampsora larici-populina Kleb. in New Zealand.

TAB LE 1. Reaction, of poplar leaf discs to two 1979 cottections of

Melampsora larici-populina

Accession Number 2

Clones Tested

S, J, Latch and A, G, Wilkinson

1

Aokautere Science Centre, Ministry of Works and Development, Palmerston North, New Zealand

P. nigra "ltalica' P. x eor. 'Altichiero' " 'Carpaccio' "

'Hevo

"

'Dorskamp'

" 'Robusta' P. x cendicsns

New poplar clones recently introduced into New Zealand from Italy have shown clear-cut differences in reaction to Melampsora larici-populina Kleb. at two widely separated locations, suggesting physiologic specialisation of the pathogen, The differential reactions observed in the field have been confirmed using in vitro inoculation of poplar leaf discs and two rust races or groups of races were distinguished on the basis of differential pathogenicity, The european poplar rust Melampsora larici-populina and the american poplar rust Melampsora medusae Thurn. were both introduced into New Zealand in 1973 (5), Since then M. larici-populina has become established as the more important rust and is widespread throughout both North and South Islands, It overwinters mainly on the semi-evergreen Populus nigra L. 'Sempervirens' which had been widely planted before the introduction of the rusts, In some areas larch and poplar grow in proximity and aeciospores from larch account for a small proportion of spring infections of poplar. M. medusae appears to be restricted to an area around Palmerston North where a few susceptible semi-evergreen P, x euramericana (Dode) Guiner clones are grown on which the rust overwinters,

19 858 860 462 566 23 5

P. x euramericana

P. x euramericana

'Altichiero' ex Whangarei

ex Palmerston North

+ + +

+ +

"·78'

+

+ -

Footnotes to Table 1 Reaction: + uredosori present; - uredosori absent 10 days after inoculation. 2 Accession numbers of the Plant Materials Centre, Aokactere Science Centre,

1

Pelmerston North,

tamination between rust collections, but hyper parasites were sometimes a problem. Leaf discs were placed on 1.5% water agar, leight discs per 9cm petri plate and were maintained at room temperature (approx. 16-25°C) and natural daylight. Rust developed in 7-10 days. Clones were rated on a simple plus/minus basis indicating uredosori present or absent 10 days after inoculation. The pathogenicity of two rust collections to seven poplar clones is given in Table 1. The Palmerston North race (or grou p) is tentatively designated as NZ-1 and the Whangarei race (or group) as NZ-2. Collections of rust on P. nigra 'ltallca' made in widely separated localities of the North Island all proved to be Race NZ-1. Rust collections from Whangarei in the 1978-79 season were Race NZ-1 on P. nigra 'ltalica' and Race NZ-2 on italian hybrids P. x euramericana 'Altichiero', 'Car paccio', 'Giorgione', 'Tie polo' and 'Veronese'. In the 1979-80 season Race NZ-2 did not appear in the Whangarei district, suggesting that it had failed to overwinter there. However, in Palmerston North Race NZ-2 appeared towards the end of the season as a small proportion of the rust population. Race NZ-2 was also found in Taranaki district on P. x candicans Ail. It is evident that different physiologic races of M. lericipopulina occur in New Zealand. The relative proportions of races in any district would depend on the particular poplar clones grown in the area, which would exert a selective influence on races of different pathogenicity. It would also depend on the competitive ability of races on clones such as P. nigra 'Italica' and P. x euramericana 'Robusta', susceptible to both races. In this preliminary study the inoculum used was derived from field collections from single clones. Further investigations to determine types of resistance should in-

Physiologic specialisation in M. larici-populina has been reported from Holland (3, 4) and Australia (1,2). In New Zealand, reaction of various poplar clones to M. tericipoplina was consistent from one season to another from 1973-1978 apart from minor variations which were attributed to climatic differences (C, W. S. van Kraayenoord, personal communication). In 1976 several new P. x euramericana hybrid clones were introduced from Italy, where they had been selected for resistance to M. allii-populina Kleb. (not present in New Zealand). Reaction to M. larici-populina was not specified. The hybrids were grown in Palmerston North during 197778 where most were found to be resistant to M. lericipopulina, but susceptible to M. medusae. In winter 1978 cuttings from the above clones were planted near Whangarei, approximately 700 km north, where in April 112

Pathogenicity tests were carried out on suckers of hazenlut (var. " Kentish Cob") using 5-6 day old cultures of the bacterium grown on glucose - yeast extract - ca rbonate - agar (GYCA) (2) at 25°C. The suckers were grown in a growth cabinet under supplementary lighting (16 h day length) at a temperature of C 26°C. They were inoculated by atomizing a suspension of the bacterium in ster ile water (C 10' cells /ml) on to leaves and stems . Immediately prior to inoculation the stems were inj ured by pr ic king with a sterile needle. Suckers treated similarly and atomized with sterile water were used as controls . All treated plants were ma intained at high humidity for thr ee days, in the growth cab inet, by covering them with plastic bags. Symptoms of the disease appeared on leaves and stems seven days after inoculation, and a yellow coloured bacterium was consistently re- iso lated on King B med ium from affected areas .

volve the use of monouredosoral isolates, quantitative inoculation techniques and quantitative assessment of infection .

REFERENCES (1)

Heather , W . A ., and S harm a, J . K. (1977 ) - Some asp ec ts of pop lar r ust rese arc h in A ustralia. Australian Forestry 40: 28 -43.

(2)

Sh arma. J . K.. and Heather , W. A . ( 1976) - P hys io log ic spe cialisatio n in pop lar lea f rusts , Melampsora medus ae Thurn. and M . laric i-popu l in a K leb. in Austral i a . Proceed ings XIX Se ss ion Disease Work ing Group, Int ernational Po plar Comm ission , France, September 1976 .

(3)

van Vloten , H. (1944) - Is ve rrij ki ng van de mycoflora . mogelijk? (Is enrichment of the mycoflora possib le? ). Tijdschrift voor Plantenziekten 50: 49 -62 .

(4)

van Vloten, H. (1949) - Kruisingsproeven met rassen van Melampsora larici-populina Klebahn. (Crossing experiments with strains of Melampsora larici-populina Klebahn.) Tijdschrift voor Plantenziekten 55: 196-209.

(5)

W ilkin son , A . G ., and Sp iers, A. G . (1976) - Introduction of the poplar rusts Melampsora larici -poplina and M. medusae to New Zeala nd and th e ir subsequent distribution . Ne w Zealand Journal of Science 19: 195-198.

The causal bacterium was a Gram negative rod, 1.8-3.2 x 0.5-0.7,tim, motile by a single polar flagellum. Results of biochemical and physiological tests carried out with the hazelnut bacterium, compared with those reported for the X. campestris group (1, 2), are shown in Table 1. On the basis of these results and results from pathogenicity tests the causal bacterium was identi fied as X. campestris iv. corylina (Miller et al . 1940) Dye 1978 (1 , 2, 3, 5). This report constitutes the first record of occurrence of bacterial blight of hazelnut in Australia. Examination of herbarium specimens ind icated that a sample of hazelnuts with identical spotting on the husks, as described here, was received from Wand iligong in January 1977 , though the disease was not identified at that time. It is probable that the disease has been present in Victoria for many years though hitherto unrecognized .

NEW DISEASES Bacterial Blight of Hazelnut D. L. S. Wimalajeewa and W . S. Washington Plant Research Institute, Burnley, Victoria 3121

Diseased specimens and a culture of the bacterium were lodged at the Plant Research Institute Herbarium, Department of Agriculture, Victoria (VPRI-11 086) . Cultures were also deposited in the Culture Collection of the Department of Microbiology, Un iversity of Queensland, Queensland (UQM - 2135 and 2136) .

Diseased specimens of hazelnuts (Corylus avellana L.) were received from a grower at Hoddles Creek, Victoria in January 1980. Inspection of affected trees (5 yr old) in the field revealed the following symptoms. Leaves showed numerous angular water-soaked spots (2-3 mm dia.) which later turned reddish brown. Young shoots and twigs bore oval shaped dark brown lesions (1-3 mm dia.) which were slightly sunken. On branches and limbs the disease caused cankers which sometimes girdled the stem. Fruits bore reddish brown spots (1-3 mm dia.) on the husks (Fig. 1). Occasionally irregular dark brown to black lesions (2-4 mm dia .) were found superficially on the nuts. The above symptoms resemble those described by Miller et al. (4) for filbert bacteriosis (bacterial blight of hazelnut) , caused by Xanthomonas campestris pv . corylina (Miller et al . 1940) Dye 1978 (X. corylina (Miller et al.) Starr and Burkholder 1942), in Oregon , U.S.A . A survey of hazelnut plantings, carried out during February-July 1980, showed that the disease is widespread, being found in three locations (Bright, Wandiligong and Stanley) in north-eastern Victoria , and in four locations (Hoddles Creek, Mt Dandenong, The Patch and Toolangi) in southern Victoria. It has been found in plantings ranging from about 5 to 30 years old . A bacterium producing yellow colonies on King B medium (3) was consistently isolated from diseased tissue. It produced abundant, mucilag inous, glistening light yellow growth on nutrient agar containing 5% sucrose. Three isolates were obtained from d iseased material collected from Hoddles Creek and Toolangi. All the isolates were used in characterization studies , while only the Hoddles Creek isolates were used to test pathogenicity.

.:!~ ~; . . :'; .. ,'.1' I .(

-

.. ,r ' ' . ~- ~ .". .

"#

1P'

Figure 1. Symptoms of bacterial bl ight on stems and husks .

113