Identification of Potato Varieties Resistant to Late Blight under Different Agro-Ecological Conditions in Nepal

Late blight caused by Phytophthora infestans (Mont.) de Bary is an economically important disease of potato causing substantial yield loss each year in Nepal. Screening potato genotypes for resistance to P. infestans under different agro-climatic conditions is one of the most important activities of potato research prior to advancing yield evaluation and release of varieties for commercial production. In 2006 and 2007, potato varieties were screened at Parawanipur (Terai, 115 masl), Sharadanagar (inner Terai, 270 masl) and Khumaltar (mid hill, 1360 masl) under natural epiphytotic conditions where late blight severity on a susceptible variety reaches 100% foliar infection. Late blight susceptible potato varieties ('Kufri Sinduri' at Parawanipur and 'Kufri Jyoti' at Khumaltar) were planted after each set of nine test rows at the spacing of 25 cm x 60 cm and were also used as boundaries of experiments to increase the inoculum pressure on tested varieties. Potato varieties CIP 392657.8, CIP 384321.15, CIP 392637.10, CIP 393280.57, CIP 393077.159 and LBr40 were consistently found to be resistant to late blight over years and different agro-climatic conditions.