77 LATE BLIGHT SCENARIO IN WESTERN UTTAR PRADESH AND CHARACTERIZATION OF PHYTOPHTHORA INFESTANS POPULATION USING BIOLOGICAL MARKERS Anju Rani, M. Narayana Bhat, B.P. Singh 1 , P.H. Singh 2 and D.K. Rana 1 Central Potato Research Institute Campus, Modipuram-250 110, UP, India 2 Central Potato Research Institute, Shimla-171 001, HP, India ABSTRACT: A survey was taken up during crop seasons of 2003-2004 and 2004-2005 in Baghpat, Muzaffarnagar, Meerut and Ghaziabad districts of western U.P for assessing late blight severity. In general, late blight severity was high during 2004-2005 in most of the localities and ranged from 4.3-81%. During 2003-2004, disease severity ranged from 2.5 to 68.8%. Ghaziabad and Baghpat districts were worst affected. A 1 mating type (old strain) was dominant in all the four districts. Most of the isolates collected from the four districts were metalaxyl sensitive. Race complexity of 7 and 8 genes were detected from Meerut while race complexicity of 5, 8, 9; 7, 8; and 5, 7, 9 genes were recorded from Baghpat, Muzaffarnagar and Ghaziabad districts, respectively. Several late blight resistant varieties have been introduced in the plains in the recent past. This might affect both the pace and direction of race development of Phytophthora infestans. A 2 mating type was first detected during mid 1990’s in the plains (Singh and Shekhawat, 1999) and since then it has spread to new locations. Information on new mating type both in time and space is required for keeping a watch on pathways of disease epidemiology. Tolerance to metalaxyl was detected way back in Nilgiri hills (Arora et al., 1992) and since then tolerant strains have been detected from other parts of the country also (Gupta et al., 1999). In the present study, survey for the occurrence of late blight was conducted in four districts of western U.P. during the crop seasons of 2003-2004 and 2004-2005, and P. infestans isolates were collected and characterized using biological markers. In all, 13, 10, 10 and 9 villages from Meerut, Muzaffarnagar, Ghaziabad and Baghpat districts, respectively, were surveyed. Only those villages were selected where highly susceptible cv. Kufri Bahar was grown on large area. Survey was carried out twice during the crop season. Observations on disease severity were recorded using the scale developed by Henfling (1987). In each village, at least 10 fields were surveyed and in each field observations were recorded on 10 random sites of plot size approximately 3 m x 3 m. Two hundred twenty three P. infestans isolates were collected and analyzed for mating type, sensitivity to metalaxyl and physiological races. During 2003-2004, late blight was first reported during the second week of December at Jat Munjhara village in Muzaffarnagar district, while during 2004-2005, it was first noticed in third week of December at Alipur village of Meerut district. In general, late blight severity was high during 2004-2005 and ranged from 4.3 to 81% whereas during 2003-2004, disease severity ranged from 2.5 to 68.8% in different districts. Ghaziabad and Baghpat districts were worst affected. Analysis for mating type revealed that the population of new strain (A 2 mating type) has been reduced considerably during the recent past (Table 1). Its frequency ranged from 0 (not detected) in Ghaziabad to 7.1% in Muzaffarnagar district. These results are at variance with the results obtained from temperate highlands of the country where new strain has completely displaced the old strain (Singh et al., 2005). Table 1. Mating type and metalaxyl sensitivity of P. infestans isolates collected from four districts of western U.P. District 2003-2004 2004-2005 Mean Mating Metalaxyl Mating Metalaxyl Mating Metalaxyl type (%) sensitivity (%) type (%) sensitivity (%) type (%) sensitivity (%) A1 A2 S IR R A1 A2 S IR R A1 A2 S IR R Meerut 96.4 3.6 96.4 3.6 0 93.8 6.3 96.9 3.1 0 95.1 4.9 96.7 3.3 0 Baghpat 91.7 8.3 100 0 0 96.3 3.7 100 0 0 94.0 6 100 0 0 Muzaffarnagar 92.9 7.1 100 0 0 92.9 7.1 100 0 0 92.9 7.1 100 0 0 Ghaziabad 100 0 92.9 7.1 0 100 0 96.4 3.6 0 100 0 94.7 5.4 0 S= sensitive; IR= intermediate resistant; R= Resistant Potato J. 34 (1-2) : 77-78, 2007