Diaporthe phaseolorum causing dieback disease on Melia dubia cav. in Karnataka state (India)

Melia dubia is an important tree species grown worldwide for its medicinal and timber values. It is widely used in timber and pulp industry and also as an organic pesticide, fertilisers, agro-forestry and herbal formulations. During 2019-2022, a dieback disease in plantations of M. dubia was recorded in Mysore, Mandya, Chamarajanagar, Hassan and Tumkur districts of Karnataka state (India) with disease incidence of 26.25%. The associated pathogen was isolated on PDA medium and its morpho-cultural characteristics were studied. The genomic DNA of the pathogen was isolated, and rDNA was amplified and sequenced using universal primers. Based on the microscopic, morpho-cultural, sequence data and phylogenetic analysis, the pathogen was identified as Diaporthe phaseolorum (Cooke & Ellis) Sacc. Koch's postulates were performed both in vitro and in vivo and the typical symptoms of dieback disease were recorded on post-inoculated saplings. The dieback disease is responsible for the poor growth of Melia species in the region, and hence, there is an urgent need to manage the disease in plantations using integrated management practices. This is the first report of the occurrence of D. phaseolorum on M. dubia plantations in India.