Phenotypes of Phytophthora infestans collected in England and Wales from 1985 to 1988: mating type, response to metalaxyl and isoenzyme analysis

Abstract

In a survey of 1864 isolates derived from samples of Phytophthora infestans obtained from potato and tomato collected in England and Wales between 1985 and 1988, the A2 mating type was identified in approximately 10% of samples. There was no evidence for an overall increase in the frequency of the A2 mating type over this period. In agar culture, A2 isolates exhibited a distinct lumpy‐colony morphology. Lumps were made up of intensely dichotomously branched hyphae. The incidence of resistance to metalaxyl among samples increased from 41 to 60% between 1986 and 1988. Some of the A2 isolates were resistant to metalaxyl and like other A2 isolates gave rise to progeny from in vitro matings with Al isolates. Except in one case, Al and A2 isolates were uniformly homozygous at an isoenzyme locus for glucosephosphate isomerase but isolates exhibited some variation at a peptidase locus. The source of the A2 isolates could not be established from these data.

Characterization of changes in populations ofPhytophthora infestansin Canada using mating type and metalaxyl sensitivity markers

“…In addition, no evidence of 'mixed' cultures or self-fertile isolates was obtained. Other researchers have also found that epidemics in a particular location are generally caused by single mating type populations (2,14,27,32,50), although mixed populations sometimes occur (5,34,36,44,48). Therefore, the VOLUME 20, 1998 opportunities for sexual reproduction still appear to be limited in Canada, except possibly in B.C.…”

“…Some authors have recognized an intermediate category (12,14,43,44), while others have not (31,37,38). However, the range of metalaxyl response within a group of isolates classed as resistant has often been great (41).…”

The occurrence of the A2 mating type of Phytophthora infestans in the Netherlands; significance and consequences

“…One hypothesis states that the A2 mating type arose from the Al mating type either through mutation or mitotic recombination (Shattock et al, 1990). According to Shaw (1983) mating type is coded for by one gene with two alleles.…”

Phenotypes ofPhytophthora infestans in Nepal: mating types and metalaxyl sensitivity

“…No A2 was recorded from the terai ( Table 1) and none of the isolates tested was self-fertile. All A2 isolates exhibited a distinct colony morphology and lumpiness in Rye A agar as did those observed by Shattock et al (1990). Such lumpiness was due to aggregation of dichotomously branched aerial hyphae.…”