PHENOTYPIC AND GENOTYPIC CHARACTERISATION OF ESTONIAN ISOLATES OF PHYTOPHTHORA INFESTANS IN 2004-2007

Abstract

SUMMARY A collection of 432 single-lesion isolates of Phytophthora infestans collected from blighted potato foliage during 2004-2007 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 Jogeva 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.