STUDIES ON ALTERNARIA LEAF BLIGHT OF ONION {Allium cepa L.)
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Date
2001-08-06
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK BANGALORE
Abstract
Among the several diseases, Alternaria leaf blight is one of the most
destructive foliar disease which causes heavy loss in onions. The causal organism
of the disease is Alternaria porri (Ellis) Ciff. Studies on Alternaria leaf blight of
onion includes, survey for incidence of disease in parts of northern Kamataka,
effect of date of sowing on the incidence of the disease, evaluation of varieties for
disease resistance, cultural and nutritional studies, in vitro and in vivo evaluation
of fungicides.
Survey for incidence of Alternaria leaf blight in parts of northem Kamataka
revealed that disease was moderate during Kharif\999. The conidiophores were
straight or flexuous, septate, pale brown in colour and measured 120 qm in long
and 6-10 qm thick, with one or several conidial scars. The fungus reached
maximum growth on 12th day of incubation in potato dextrose broth. Potato
dextrose medium supported maximum growh of Alternaria porri (Ellis) Ciff.
Arabinose and potassium nitrate were found to be best carbon and nitrogen sources
for the growth of Alternaria porri (Ellis) Ciff respectively.
The highest incidence of the disease was recorded in the early sown
crop. But the incidence decreased in late sown crop. Screening of onion
genotypes indicated that none of the cultivars were immune and resistance to the
disease. But only one genotype Arka kalyan showed, moderately resistant reaction
to the disease.
In vitro evaluation studies indicated that, mancozeb (Indofil, M -45) and
difenoconazole (score) were found to be best systemic and non systemic
flingitoxicants against the pathogen respectively. Mancozeb is the best fungicide in
controlling the spread of Alternaria leaf blight under field condition. The bulb
yield and cost benefit ration were high in mancozeb sprayed treatment.
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