Investigations on Chrysanthemum Leaf Blight Caused by Alternaria alternata (Fr.) Keissler
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Date
2011
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UAS, Dharwad
Abstract
Among the several diseases, Alternaria leaf blight is one of the most
destructive foliar disease which causes heavy loss in chrysanthemum. Survey during
Kharif/Rabi 2010 revealed that Alternaria leaf blight was severe in all five districts
viz., Dharwad, Haveri, Gadag, Koppal and Belgaum. Isolation and morphological
studies revealed Alternaria alternata (Fr.) Keissler as causal organism. In cultural
studies maximum growth was observed in potato dextrose agar (81.60mm), followed
by Richard’s agar (78.50mm). Nutritional requirement of the pathogen were studied
with different carbon and nitrogen sources. Among carbon compounds, mean dry
mycelial weight of the pathogen was maximum in glucose (359.67mg), followed by
sucrose (276.62mg). Among the nitrogen sources, maximum mean dry mycelial
weight was observed in Asparagine (383.33mg). In pH studies maximum growth of
pathogen found at 6 pH. The maximum growth was observed, when cultures were
exposed to alternate cycles of 12hr light and 12hr darkness. Optimum temperature
range for the growth of the pathogen was found to be between 25ºC -30ºC.
The survival of pathogen in chrysanthemum crop debris was more than 183
days under in all three different conditions viz., refrigerator, glasshouse, Laboratory,
Out of nine hosts range studies, sunflower and day flower produced symptoms.
Among the five chrysanthemum varieties screened for their reaction to leaf blight
under artificial conditions all are show the susceptible reaction. Among ten different
fungicides tested in vitro, Propiconazole, Difenconazole, Penconazole and
Hexaconazole at 0.1% concentrations completely inhibited the mycelial growth of A.
alternata.
In case of field evaluation of fungicides Hexaconazole (0.1%) effectively
controlled the disease incidence and recorded very less per cent disease index (5.18)
which was on par with the Difenconazole (0.1%) having a per cent disease index
(5.74).
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Plant Pathology