STUDIES ON GREY LEAF SPOT OF COCONUT CAUSED BY Pestalotia palmarum Cooke
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Date
2001-08-04
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK BANGALORE
Abstract
An investigation was undertaken to study the different aspects of grey
leaf spot of coconut caused by Pestalotia palmarum Gooke.
The fungus was found to survive in the infected debris in the ground
for two months and serve as the primary source of infection. Oilpalm was found to
act as a collateral host for the survival of the fungus.
The pathogen was found to be a wound parasite. In older leaves
early infection and symptom development were observed.
Alternate cycles of light play a major role on disease development.
The fungus produced maximum mycelial growth on exposure to 12 hours light first
followed by 12 hours darkness. Sporulation was found to be excellent under 12
hours darkness first then 12 hours light and good under continuous darkness.
The disease manifests during cool and dry months and intensive
blighting occurs in summer months. Per cent disease index was found to be
negatively correlated with weather parameters viz., maximum and minimum
temperature, rainfall and relative humidity.
Parthenium and Ocimum leaf extracts showed high fungitoxic value
against the fungus.
The fungus Trichoderma viride produced 82.70% inhibition of mycelial
growth of Pestalotia palmarum. The bacterium Pseudomonas fluorescens also
inhibited the growth of the fungus.
Of the nine fungicides evaluated against the fungus, Carbendazim
(0.1%), Triademefon (0.1%), Tridemorph (0.1%), Hexaconazole (0.1%),
Propiconazole (0.1%) and Mancozeb (0.2%) showed complete inhibition of the fungal
growth.
Under in vitro conditions systemic chemicals were found to be most
effective against the pathogen followed by plant extracts.
Out of the six varieties and two hybrids screened, the dwarf varieties
viz., Chowghat Dwarf Orange, Chowghat Dwarf Green and Malayan Dwarf Yellow
showed resistant reaction.
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