MSc

The study entitled ‘Foliar fungal pathogens associated with yellowing disease of coconut’ was conducted at the Department of Plant Pathology, College of Agriculture, Vellayani.
A detailed survey was undertaken to study the incidence and intensity of Root (Wilt) Disease and Yellowing disease in the Instructional Farm, Vellayani. Both the diseases were observed in all the six blocks of the Farm. Out of 6107 palms in the farm 561 palms were affected by Root (Wilt) Disease (9.19 %) and 127 palms (2.08%) were showing symptoms of Yellowing disease. A total of 242 (43%) Root (Wilt) affected palms and 94 (74%) Yellowing disease affected palms are to be cut and removed since they are unproductive.
The characteristic symptoms of Root (Wilt) Disease were flaccidity, ribbing, yellowing and necrosis. The Root (Wilt) Disease affected palms (42%) were ‘super infected’ with leaf rot disease also. In Yellowing Disease affected palms sudden appearance of chlorosis/ yellowing/ bronzing of one or more leaves in the middle whorl coupled with flaccidity was the characteristic symptom. Rapid drying and necrosis of inflorescence, abnormal shedding of flowers, buttons, immature nuts and mature nuts occurred in succession either simultaneously or prior to yellowing and the palms became barren within a short period. On the chlorotic/ yellowed leaves intense brown to black leaf spots developed which enlarged, coalesced together and blighted the leaflets. The affected palms usually succumb within a short span of time.
Foliar fungal pathogens associated with leaf spots/ blights on the symptomatic leaves of Yellowing disease affected palms were isolated and the pathogenicity was proved. On artificial inoculation on detached spindle as well as mature leaflets, the pathogens produced tiny brown water soaked lesions of angular or oval or irregular shapes. Among the different pathogens Chalara fimbriata was the most virulent one. Based on the morphological and cultural characteristics the following foliar fungal pathogens on Yellowing disease affected palms were identified: Alternaria alternata, Aspergillus niger, Colletotrichum gloeosporioides, Cephalosporium spp., Chalara fimbriata, Curvularia spp., Fusarium verticillioides, F. semitectum, Lasiodiplodia theobromae, Pestalotiopsis maculans, Pestalotiopsis palmarum, Phomopsis spp., Arthrinium spp. and Verticillium spp. Among them, L. theobromae, C. gloeosporioides and P. maculans were the most frequently isolated pathogens.
The biochemical analysis revealed that total sugars, total soluble proteins and phenylalanine ammonia lyase activity were higher in the leaves of diseased palms.
Among the nine fungicides tested in vitro, Propiconazole, Tebuconazole and Mancozeb were found to be equally effective against L. theobromae, C. gloeosporioides, P. maculans and F. verticillioides.