Ngô Hải Xuyên, Hoàng Văn
Summary
388 isolates of the late blight fungus were collected from potato and tomato grown in Ha Noi, Hung Yen, Ha Tay, Bac Giang, Bac Ninh, Lao Cai and Da Lat. 320 isolates were successfully to tested for A1 mating type (82,5%). The pea-agar and pea-selective culture media were optimal for mycelium development of Phytophthora infestans, while V-8 medium was good for sporangia formation. Four tomato cultivars (TS-33, Wva-7 00, L-3708, LA-3708) and one potato cultivar (Diamant) showed resistant reaction. 11 isolates cultured on the pea-agar showed moderate resistance to Metalaxyl. Keywords: Phytophthora infestans, isolates, pea-agar media, tomato and potato, Metalaxyl.