New Zealand Journal of Crop and Horticultural Science abstracts
Characterisation of pathogenicity of Phytophthora parasitica isolates by
stem and detached-leaf inoculations in four tobacco cultivars
CÉCILE ROBIN*
DAVID GUEST
School of Botany
University of Melbourne
Parkville, Vic 3052
Australia
*Present address: Institut National de la Recherche Agronomique, Station de
Pathologie Végétale, Centre de Bordeaux, BP 81, 33 883 Villenave
d'Ornon, France.
Abstract The response of four cultivars of tobacco (Nicotiana
tabacum) to eight Australian and exotic isolates of Phytophthora
parasitica and one of P. cryptogea was studied using stem and
detached-leaf inoculations. With both techniques cultivars differed in their
susceptibility to pathogen colonisation, which was strongly dependent on the
cultivar-isolate interaction. The ability to cause expanding lesions on
inoculated stems differentiated some tobacco isolates that were particularly
aggressive from less aggressive tobacco isolates, and from isolates from tomato
and carnation. Virulence on cultivar `NC2326' identified two of the tobacco
isolates as race 1, one from Australia (9201) and one from Cuba (309). P.
cryptogea induced some foliar systemic necrosis in three cultivars. Four
P. parasitica isolates, one from carnation and two from tobacco,
exhibited a similar toxicity only on the cultivar `Samsun'. On wounded detached
leaves both non-tobacco and tobacco isolates initiated lesions. The length of
lesion reflected their relative aggressiveness, but not their virulence, on
tobacco. On the basis of their pathogenicity in both stem and leaves, tobacco
isolates were not separated from non-tobacco isolates, but significant
differences of both aggressiveness and virulence were observed among P.
parasitica isolates.
Keywords tobacco; Phytophthora parasitica; black shank
disease; host specificity
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