Cd. Therrien et al., PHYTOPHTHORA-INFESTANS IN POLAND FROM 1987-1989 - NUCLEAR-DNA CONTENT, MATING-TYPE DISTRIBUTION AND RESPONSE TO METALAXYL, Journal of phytopathology, 139(1), 1993, pp. 68-80
Isolates of Phytophthora infestans were collected from all potato grow
ing regions of Poland during the blight seasons of 1987-1989. All 1987
isolates were of A1 mating type and were sensitive to metalaxyl. In 1
988 and 1989, 46.5 % and 55.3 % of the isolates were sensitive to meta
laxyl, respectively. The percentage of highly resistant (R) isolates i
ncreased from 25.6 % in 1988 to 39.5 % in 1989; however the percentage
of intermediately resistant (1) isolates decreased during that period
from 27.9 % to 5.3 %. A significant association was observed between
the A1 compatibility type and metalaxyl resistance. The A2 mating type
first appeared in 1988, and its frequency increased from 4.7 % of the
population in 1988 to 47.6 % in 1989. Coincident with this change in
mating type frequency, changes in ploidy levels of isolates were obser
ved. Whereas 3 % of the 1988 isolates were diploid, 90 % of the 1989 A
2 isolates and 28.6 % of the 1989 A1 isolates were diploid. The approx
imate 1 : 1 ratio of the two mating types encountered in 1989, and the
predominance of diploidy, indicates that the Polish population of P.
infestans has the potential to become sexual.