012_JPP720(Runno)_375

A collection of 432 single-lesion isolates of Phytophthora infestans collected from blighted potato foliage during [2004][2005][2006][2007] in Estonia, were analyzed for virulence (all isolates), mating type (424 isolates) and response to metalaxyl (412 isolates). The samples came from 25 fields comprising conventional production in central, northern, southern, south-eastern and southwestern regions and from untreated experimental field trials at Jõgeva Plant Breeding Institute in eastern Estonia. Of the isolates 33% were A2 mating type. Both mating types were present in all fields; the frequency of A2 mating type varied from 3% to 71%. In the context of specific virulence, the Estonian population had a very low frequency of virulence against R5 (17%) and R9 (3%). The most common pathotype was 1.3.4.7.10.11. A subgroup of 57 isolates was assessed for mtDNA haplotype and RG57 fingerprints. Three mitochondrial DNA haplotypes, i.e. Ia (51%), IIa (42%) and IIb (7%), were found. Twenty-one RG57 fingerprints were detected. The four most common fingerprints represented more than half of the isolates (67%). On the basis of combined markers, thirty-three multilocus genotypes were identified, of which 81% were detected only once. Genotypic diversity measured by the normalized Shannon diversity index was 0.79. The data indicate that the Estonian population of P. infestans is diverse, having a large number of multilocus genotypes and both mating types within fields, with potential for sexual recombination and spread of fungicide resistance