Epidemiology and Management of Purple Blotch of Onion Caused by Alternaria porri (Ellis) Cif.
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Date
2012
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Publisher
UAS, Dharwad
Abstract
Onion (Allium cepa L.) (2n=16) one of the most important commercial
vegetable crops of India belonging to the family Alliaceae. Purple blotch caused by
Alternaria porri (Ellis) Cif. is a destructive disease and causes extensive damage to
bulbs as well as seed crop. Survey during kharif 2011, revealed that, highest per cent
disease index (69.33) was noticed in Vonnali village in Uttara Kannada district. While
the lowest (17.33) was recorded in Annigeri village in Dharwad district. On the basis
of morphological and pathological studies, the pathogen was identified as Alternaria
porri (Ellis) Cif. The pathogen was grouped into six isolates viz., Dharwad, Gokak,
Savanur, Navalgund, Mundargi and Kumta isolates. The cultural and morphological
characters were studied on different media where the growth was fast in Czapeks Dox
medium and slow growth in the Corn meal agar. The weather studies revealed that
PDI was progressing at linear rate throughout the plant growth and it was negatively
correlated with minimum temperature, relative humidity (morning and evening).
While, positively correlated with maximum temperature and negatively non
significant with rainfall. Out of twelve different fungicides tested in vitro, Zineb 68%
+ Hexaconazole 4%WP, Mancozeb 75%WP at all the concentrations completely
inhibited the mycelial growth of Alternaria porri. Among the six plant extracts, garlic
clove extract and NSKE extracts were highly inhibitory to Alternaria porri, while
periwinkle leaf extract proved to be least inhibitor. Among six bioagents,
Trichoderma harzianum was most effective. In case of field evaluation field
evaluation of different fungicides botanicals and bioagents indicated that, lower
disease index (30.66), high bulb yield (20.60 t/ha) and maximum B:C ratio (5.30) was
recorded in plots receiving three sprays of Avatar (0.15%). In botanicals and bio
agents Garlic clove extract @ 5 per cent recorded highest yield of (16.13 t/ha) and
incremental B:C ratio of 4.07.