"STUDIES ON MANGO GUMMOSIS WITH SPECIAL REFERENCE TO Lasiodiplodia theobromae (Pat.) Griffon & Moube"

Field: Agricultural and Biological Sciences (Life Sciences)

Mango (Mangifera indica L.) is one of the world’s most important and esteemed fruit of the tropical and subtropical world and is cultivated extensively as a commercial fruit crop in India. Mango gummosis incited by Lasiodiplodia theobromae (Pat.) Griffon & Moube [synonym: Botryodiplodia theobromae] is becoming a serious problem in India on many popular varieties of mango particularly during monsoon and post-monsoon periods. Survey was conducted to assess the incidence of gummosis in the major mango growing areas of Andhra Pradesh,viz., Krishna, Khammam, Rangareddy andMedak during June to October,2013.During the survey gummosis incidence was assessed and symptoms characteristic of the disease,viz.,gummosis, dieback, and vascular discoloration were noticed in the orchards surveyed. Among the four districts surveyed, maximum disease incidence (13.3 per cent) was recorded in the cultivar, Chinnarasamand least incidence was recorded in Baneshan (2.0 per cent) and kobbarimamidi(2.0 per cent) cultivars at Rekunta village of Krishna district. Growth rate of L. theobromae on different solid media at different temperatures was studied. The radial growth of the mycelium was maximum (8.89 and 8.83) on PSA medium at 30 and 35C followed by PDA (8.46) at 35C. Least mycelial growth (6.3) was observed in MEA at 25C. The maximum pycnidial production was observed on OMA followed by PDA at temperature above 30C. Least pycnidial production was observed on MEA at all the temperatures tested. The fungal growth on various media was categorized as circular with sparse aerial mycelium, circular with moderate aerial mycelium and circular with abundant mycelium. The color of colony ranged from whitish grey to blackish grey. The pathogen was isolated from infected host plant, purified and identified as L.theobromae and pathogenicity was proved by stem inoculation method. Morphological characters of L. theobromae were studied and following observations were made. Colonies were grey-brown to black with dense aerial mycelia on the PDA medium. Pycnidia were separate or aggregated, dark brown, thick or thin-walled. Conidiophores were hyaline, cylindrical to subobpyriform, with oblong, straight and hyaline single celled conidiaandinitially. Gradually the conidiabecame dark brown and produced one septum with longitudinal striations; the size of conidia measured 22-29×11–15 μm. Efficacy of nine fungicides was tested in vitro against L. theobromae, of which carbendazim, carbendazim + mancozeb and propiconazole were found superior at both 250 and 500 ppm concentrations with 100 per cent inhibition of the test pathogen. However, mancozeb and propineb were found effective only at 500ppm concentration. Among the botanicals and Trichoderma isolates tested in vitro, Garlic bulb extract and Trichoderma isolates T9, T6, T3 and T2 were found effective against L. theobromae. Screening of ten different mango cultivars against L. theobromae by stem inoculation method revealed that Chinnarasalu, Manjeera, Tellagulabi and Suvernarekha were susceptible to gummosis, while Baneshan, Alphonso, Imam Pasand and Pandurivarimamidi were moderately resistant. Among the cultivars screened, Suvernarekha wasfound highly susceptible to mango gummosis.