Survey was conducted for the assessment of leaf blight incidence in coconut growing districts of Tamil Nadu. The leaf blight incidence was ranged from 3.76 to 28.20 per cent in the surveyed areas and the maximum incidence was recorded in Pollachi area (28.20 per cent). Among the fifteen isolates of Lasiodiplodia theobromae collected, the isolate collected from Aliyarnagar (LT-CL1) produced maximum lesion size of 6.7 × 5.5 cm and it was proved to be virulence. The colony texture of the L. theobromae isolates varied from fluffy, suppressed to raised and the colour varied from dull white to greyish black. All the isolates showed variation in the morphological characters and the pycnidiospore size varies from 14.3 × 7.69 μm (LT-CL2) to 25.59 × 13.31 μm (LT-CL5). The Lasiodiplodia genus showed the amplicon size of 550bp with respect to the region of the 18S-28S rRNA intervening sequence. The fungal pathogen of leaf blight of coconut was identified as L. theobromae based on its morphological and molecular characters.
Key words : Coconut, Leaf blight, Lasiodiplodia theobromae, Morphology, Molecular characters.