Phytopathology. 1998 Sep;88(9):939-49. doi: 10.1094/PHYTO.1998.88.9.939.
ABSTRACT Dramatic changes occurred within populations of Phytophthora infestans in the United States and Canada from 1994 through 1996. Occurrence of the US-8 genotype, detected rarely during 1992 and 1993, increased rapidly and predominated in most regions during 1994 through 1996. US-7, which infected both potato and tomato and made up almost 50% of the sample during 1993, was detected only rarely among 330 isolates from the United States analyzed during 1994. It was not detected at all in more limited samples from 1996. Thus, ability to infect both potato and tomato apparently did not increase the fitness of this genotype relative to US-8, as predicted previously. US-1, the previously dominant genotype throughout the United States and Canada, made up 8% or less of the samples analyzed during 1994 through 1996. A few additional genotypes were detected, which could indicate the beginnings of sexual reproduction of P. infestans within the United States and Canada. However, clonal reproduction still predominated in all locations sampled; opportunities for sexual reproduction probably were limited, because the A1 and A2 mating types usually were separated geographically. The high sensitivity of the US-1 genotype to the fungicide metalaxyl also could have reduced opportunities for contact between the mating types in fields where this compound was applied. The previous correlation between metalaxyl sensitivity and genotype was confirmed and extended to a new genotype, US-17: all US-1 isolates tested were sensitive; all isolates of the US-7, US-8, and US-17 genotypes tested to date have been resistant. Isolates of P. capsici and P. erythroseptica, two other species often found on tomato and potato, could be easily distinguished from each other and from P. infestans using a simple allozyme assay for the enzyme glucose-6-phosphate isomerase. This technique could be useful for rapid identification of species, in addition to genotype of P. infestans. It generally was not possible to predict which genotypes would be present in a location from 1 year to the next. Long-distance movement of US-8 in seed tubers was documented, and this was probably the primary means for the rapid spread of this genotype from 1993 through 1996.
摘要 1994 年至 1996 年期间，美国和加拿大的疫霉种群发生了巨大变化。1992 年和 1993 年很少检测到的 US-8 基因型迅速增加，并在 1994 年至 1996 年期间在大多数地区占主导地位。1993 年，感染马铃薯和番茄的 US-7 占样本的近 50%，但在 1994 年分析的 330 个美国分离物中很少检测到。在 1996 年更有限的样本中根本没有检测到。因此，与 US-8 相比，感染马铃薯和番茄的能力显然并没有增加该基因型的适应性，这与之前的预测相反。US-1 是美国和加拿大的主要基因型，在 1994 年至 1996 年期间分析的样本中占 8%或更少。还检测到了一些其他的基因型，这可能表明疫霉在美国和加拿大内部开始有性繁殖。然而，克隆繁殖在所有采样地点仍然占主导地位；有性繁殖的机会可能有限，因为 A1 和 A2 交配型通常在地理上是分开的。US-1 基因型对杀菌剂金属羧酸盐的高度敏感性也可能减少了该化合物施用于田间时交配型之间接触的机会。金属羧酸盐敏感性与基因型之间的先前相关性得到了证实，并扩展到一个新的基因型 US-17：所有测试的 US-1 分离物均敏感；迄今为止测试的所有 US-7、US-8 和 US-17 基因型的分离物均具有抗性。辣椒疫霉和番茄疫霉两种经常在番茄和马铃薯上发现的其他物种的分离物可以通过葡萄糖-6-磷酸异构酶的简单同工酶分析很容易彼此区分，也可以与疫霉区分开来。除了鉴定疫霉的基因型外，该技术还可用于快速鉴定物种。通常不可能从一年到下一年预测一个地点会出现哪些基因型。远距离传播的 US-8 种薯已被记录，这可能是 1993 年至 1996 年期间该基因型迅速传播的主要途径。
