Characterisation of pathogenicity of Phytophthora parasitica isolates by stem and detached-leaf inoculations in four tobacco cultivars

Abstract The response of four cuitivars 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 cuitivars 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 cuitivars. 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 le...

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