Perpetuation and Management of Alternaria solani (Ellis and Martin) Jones and Grout Causing Early Blight of Potato in Kashmir

The present study on perpetuation and management of Alternaria solani, causing early blight of potato in Kashmir was conducted during 2008 to 2009. An extensive survey conducted in four districts of Kashmir Valley viz., Budgam, Baramulla, Srinagar and Shopian revealed prevalence of early blight of potato in all the localities surveyed. Mean disease incidence and intensity of 24.54 and 13.84 per cent were recorded in the year 2008 and that of 28.23 and 15.98 per cent during the year 2009, respectively. The disease was characterised by small irregular to circular dark brown spots on the lower leaves measuring approximately 0.5 mm in size. The spots on coalescing formed irregular patches, which later on resulted in complete blighting of leaves. The causal fungus was isolated and identified as Alternaria solani (Ellis & Martin) Jones and Grout. The maximum apparent infection rate of 0.155 and 0.165 unit/day was recorded during the second fortnight of June in 2008 and 2009, respectively. Weather factors viz., temperature, relative humidity and rainfall were positively correlated with disease intensity (66.50 per cent contribution). The pathogen perpetuated as mycelium and conidia throughout winter on diseased leaves left on the ground surface and on diseased potatoes kept in ambient store. The number of spores cm-2 leaf area and the viability of spores decreased with increase in depth of placement in soil. Maximum spores production on overwintered leaves and potatoes were observed during first fortnight of June. Disease tolerance of varying degree was observed under natural conditions in the available potato germplasm. Cultivar SM/92-338 proved tolerant to A. solani while as, cultivars Kufri himami, SM/96-127 and SM/94-44 showed moderate tolerance to the disease compared to rest of the 21 test cultivars. Evaluation of bioagents revealed that all the test bioagents were significantly effective in inhibiting the mycelial growth of A. solani under dual culture method. Trichoderma harzianm exhibited maximum mycelial growth inhibition of 71.85 per cent followed by T. viride (65.93%) and Trichoderma virens (58.65%). Evaluation of plant extracts revealed that all the test extracts were significantly superior in inhibiting the mycelial growth of A. solani at various test concentrations. Datura stramonium exhibited maximum mycelial growth inhibition of 61.12 per cent followed by Artimesia absinthium (58.54%), Juglans regia (38.31%), Mentha spicata (38.02%) and Uretica dioica (37.34%). Systemic fungitoxicants and non-systemics were tested in vitro for mycelial growth inhibition at (100-350 ppm and 1000-3500 ppm, respectively). Among the systemic fungitoxicants hexaconazole (0.03 %) followed by fenconazole (0.03%) proved significantly superior at all tested concentration, whileas mancozeb (0.2%) followed by propineb (0.2%) proved significantly superior in inhibiting mycelial growth the individual and combined effect of most effective in vitro fungitoxicant, bioagent and botanicals was also evaluated for the management of potato early blight in field. Among various treatment combinations seed treatment with mencozeb (0.2%) + foliar spray with hexaconazole (0.03%) + foliar spray with datura (50%) + foliar spray with T. harzianum (1 x 107 spores ml-1) proved significantly superior