Variability in Phytophthora nicotianae var. parasitica causing buckeye rot on tomato in north-western Himalayas

The studies were undertaken on cultural, morphological and molecular diversity in Phytophthora nicotianae var. parasitica associated with buckeye rot of tomato (Solanum lycopersicum L.) in Himachal Pradesh. Seventeen isolates of P. nicotianae var. parasitica collected from diverse tomato growing areas of Himachal Pradesh were categorized into 4 cultural groups based on colony characteristics i.e. shape of colony, colony colour, type of growth & sporulation. Test isolates were grouped into 3 categories based on morphological characteristics i.e. shape of sporangia, position of sporangia on sporangiophore, presence of papillae, size of sporangia (L x B) and L:B ratio. Genetic diversity analysis using Inter-Simple Sequence Repeat (ISSR) primers and UPGMA cluster analysis distinguished 17 isolates into two major clusters (Cluster I and Cluster II) with a similarity coefficient of 0.44 or 44 per cent. Cluster I comprised of 6 isolates and other contained 11 isolates. The cluster I was further sub-divided into 2 clades i.e. Ia & Ib (at similarity coefficient of 0.56). Cluster II was also sub-divided into 2 clades i.e. IIa & IIb (at similarity coefficient of 0.60).