Organic Management of Purple Blotch of Onion Caused by Alternaria porri (Ellis) Cif.
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Date
2013
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Publisher
UAS, Dharwad
Abstract
Onion is one of the most important commercial vegetable crops of India. The crop is
subject to attack by a number of diseases, of which purple blotch caused by Alternaria porri
is serious and also a major limiting factor in cultivation of onion. Survey during Kharif 2012-
13 revealed that purple blotch was found in all parts of Northern Karnataka and was severe in
Haveri district. Isolation and pathogenicity to onion plants was proved.
Trichoderma harzianum was most effective against A. porri, followed by T. koningii.
Among the plant extracts maximum inhibition of mycelial growth of A. porri was recorded
with Azadirachta indica followed by Ocimum sanctum.
Among the organics tested against A. porri, Cow urine followed by Neem cake was
highly inhibitory to A. porri. Among the organic combinations with antagonists tested against
A. porri, Cow urine plus T. harzianum showed maximum inhibition of mycelial growth.
Among the combinations of organics and botanicals tested against A. porri, maximum
inhibition of mycelial growth was recorded in Cow urine plus O. sanctum. Combinations of
organics and amendments were tested against A. porri; maximum inhibition of mycelial
growth was recorded in Cow urine plus Pongamia cake.
Influence of weather parameters on purple blotch of onion at different date of sowing
revealed that maximum temperature was positively correlated with number of lesions, lesion
size and per cent disease index at all four different dates of sowing and in the late sown crop
(third week of July), the disease was low compared to early sowing.
The field studies on organic management of purple blotch of onion revealed that seed
treatment with T. harzianum @ 10g/kg –spray of Panchagavya 5%+ Neem Seed Kernel
Extract 5% proved best with least per cent disease index and bulb weight, bulb diameter,
yields compared to unsprayed check.