DEMIOLOGY AND MANAGEMENT OF PURPLE BLOTCH IN ONION
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Date
2018-07
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UHF,NAUNI
Abstract
ABSTRACT
Purple blotch caused by Alternaria porri (Ellis) Cifferi is one of the major disease in
onion growing areas of Himachal Pradesh. Survey studies conducted in the present
investigation revealed that disease occurred in moderate to severe form in different onion
growing localities of Solan and Sirmour districts of Himachal Pradesh. The test pathogen was
isolated in pure culture on PDA. The microscopic examination of test fungus revealed
peculiar obclavate or obpyriform conidia with long beak. Thus, based on cultural and
morphological characters the test pathogen was identified as Alternaria porri (Ellis) Cifferi.
Pathogenicity tests revealed initial symptoms as small sunken whitish fleck which later on
became oblong with peculiar purple zonations giving target board like appearance to the
lesion. Epidemiological studies revealed that temperature of 25oC, RH of 100.0 per cent and
leaf wetness period of 24 h were optimum for the disease development reflecting
significantly high rate of infection. The results of survival studies indicated a significant
decrease in survivability of pathogen with the increase in storage duration and depth of
burial. In vitro evaluation studies reflected Cabrio Top (metiram + pyraclostrobin), Folicur
(tebuconazole), and Amistar (azoxystrobin) as most efficacious fungicides in inhibiting the
mycelial growth of Alternaria porri while amongst botanicals garlic and NSKE provided
significantly high inhibitory response. Field evaluation studies inferred the application of four
foliar sprays of Cabrio Top (metiram + pyraclostrobin) @ 0.2 per cent at ten days interval
started with the initiation of disease to be most efficacious in limiting the purple blotch of
onion (83.41%) and enhancing the bulb yield (255.32 q/ha) with ICBR ratio of 1:8.78.
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