在Memuro城镇,位于日本北海道Tokachi地区中部,主要种植田间抗病品种Matilda.1998年马铃薯晚疫病在此品种上发生较前几年早.为了了解Matilda品种抗性降低的原因,对1996-1999年Tokachi地区的晚疫病菌基因型的时间变化进行了研究及不同基因型间病菌产生病斑能力进行了比较.在1997年以前基因型JP-1在Tokachi地区占主导地位.在1997年基因型A首次在Tokachi地区被发现并且局限在Tokachi北部.在1998和1999年基因型A遍及整个Tokachi地区,1999年其比例上升至72%.用孢子囊悬浮液接种法检测不同基因型病菌对Matilda品种的致病力结果发现,基因型A比基因型JP-1和基因型B产生更大的病斑.然而通过液滴接种法所有3个基因型都可产生扩展的病斑.结果表明,Matilda减少的田间抗性是由于基因型A 传播到Memuro城镇的Matilda品种上所致.%The field resistant cultivar ‘Matilda' has been grown chiefly in Memuro town, at the central part of Tokachi district, Hokkaido, Japan. The cultivar blighted by Phytophthora infestans was unusually earlier in 1998 than that in the previous years. To know the reason why ‘Matilda' became weak, temporal change of genotypes of P. infestans was studied in Tokachi district from 1996 to 1999, and the ability to produce lesions were compared among genotypes. Before 1997, the genotype JP-1 of Phytophthora infestans was highly predominant in Tokachi district. The genotype A for the first time occurred in Tokachi in 1997, and was confined to northern Tokachi. It became common throughout Tokachi in 1998 and 1999, and its proportion increased up to 72% in 1999. The genotype A produced the higher number of lesions on ‘Matilda' than the genotype JP-1 and the genotype B by spray inoculation of sporangial suspension, while all the three genotypes produced progressing lesions by drop inoculation. The results suggested that the reduced field resistance of ‘Matilda' was due to that the genotype A spread to Memuro town, in which the cultivar was grown.
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