POPULATION CHANGES AND PHENOTYPIC DIVERSITY OF PHYTOPHTHORA INFESTANS ISOLATES FROM ESTONIA AND FINLAND
E. Runno-Paurson, A. Hannukkala, K. Kotkas, M. Koppel, I.H. Williams, M. Mänd
In Estonia and Finland, 386 and 671 isolates, respectively, of Phytophthora infestans were collected during the growing seasons of 2001-2007. Collection was from groups of potato cultivars of different origin from field plots at two research institutions in eastern and northern Estonia and from variety trials at two locations and commercial potato fields in Finland. Mating type, pathotype based on virulence on a differential set of 11 R genes of Solanum demissum and response to the fungicide metalaxyl were determined in both countries by comparable methods. The diversity of the P. infestans populations in both countries over the monitoring period was high. In Finland, the proportion of A1/A2 mating types was almost equal throughout the monitoring period, while in Estonia the A1 population, dominating in 2001-2004, shifted towards an equal proportion of both mating types in 2005-2007. The diversity of the P. infestans population, as measured by virulence pathotypes and the number of avirulence factors per isolate, developed in opposite directions in Estonia and Finland from 2001-2004 to 2005-2007: the diversity decreased in Estonia and increased in Finland. Metalaxyl sensitivity in the Estonian P. infestans population increased while in Finland it decreased during the same period. Results clearly show differences between Estonian and Finnish populations of P. infestans in several aspects, which may derive from cropping practices. The high A2 mating type percentage during 2005-2007 in both countries points to soil contamination with oospores.