2.2.56
POPULATION STUDIES ON PHYTOPHTHORA INFESTANS IN FINLAND AND NORWAY

A HERMANSEN1, M B BRURBERG1, A HANNUKKALA2 and R HAFSKJOLD3

1The Norwegian Crop Research Institute, Plant Protection Centre, Dept. of Plant Pathology, Fellesbygget, N-1432 Ås, Norway; 2Agricultural Research Centre, Institute of Plant Protection, FIN-31600 Jokioinen, Finland, 3Agricultural University of Norway, Dept. of Horticulture and Crop Sciences, PO Box 5022, N-1432 Ås, Norway

Background and objectives
The new population of Phytophthora infestans in Europe consisting of A1 and A2 mating types may have important consequences for potato late blight control [1]. The A2 mating type was observed for the first time in Finland in 1992 and in Norway in 1993. The aim of this work was to investigate if sexual reproduction is occuring and to study other traits important for the control strategy.

Materials and methods
P. infestans was isolated from potato leaves and tubers collected from different parts of Finland and Norway in 1993-96. Isolates were assessed for mating type, resistance to metalaxyl and virulence phenotype. The DNA fingerprinting probe RG57 was used to study genetic variation within and between subpopulations.

Results and conclusions

Both mating types were present in most regions of Finland and Norway. Metalaxyl sensitivity was occuring at different levels in the two countries. In Finland the proportion of resistant strains have decreased to a low level from the early 1990s when the blight population was fully metalaxyl resistant. In Norway more than half the number of isolates were resistant to metalaxyl in 1996. All known virulence genes were present in both countries (R9 not tested). The DNA fingerprinting analyses are at present not completed, but will be important for the conclusions drawn regarding the sexual reproduction.

References
1. Fry WE, Goodwin SB, Dyer AT, Matuszak JM, Drenth A, Tooley PW, Sujkowski LS, Koh YJ, Cohen BA, Spielman LJ, Deahl KL, Inglis DA, Sandlan KP, 1993. Plant Disease 77, 653-661.