Epidemiology and management of stemphylium blight of onion (Allium cepa L.) caused by stemphylium vesicarium (Wallr.) simmons
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Date
2009
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Publisher
CCSHAU
Abstract
In epidemiological studies temperature (maximum) 20.3 to 250C, temperature (minimum) 0.3
to 4.00C, relative humidity (morning) more than 82 to 89 per cent, relative humidity evening 25 to 28 per cent
have been observed congenial for the progression of the disease. The regression analysis of disease severity with
weather variables showed that temperature (maximum ) and temperature (minimum) were most contributing
factors with R2 values 0.91,0.94,0.94 and 0.92 in four dates of transplanting respectively. The correlation
coefficient analysis of disease severity concluded that temperature (Maximum) and temperature (minimum) were
significant and positively correlated with disease development. However, relative humidity (evening) was found to
be non significant, relative humidity (morning) also had a role in disease development. The stepwise regression
analysis showed that all the five weather variables produced maximum R2 value in all the four dates of
transplanting (0.95-0.98). However the two variables temperature (maximum) and temperature (minimum) were
most contributing factor and produced maximum R2 value in all the four dates of transplanting (0.91-0.94). In
survival experiment during the month of December no viable spores could be seen in the debris kept under field
and lab conditions. However the survival of the pathogen could be noticed in freeze conditions only upto 17.5 per
cent. Seven varieties/lines /genotypes were tested against Stemphylium blight of onion. None of these
varieties/lines /genotypes showed resistance against Stemphylium blight of onion. The effect of leaf extracts on
mycelial growth of the fungus under in vitro conditions revealed that neem leaf extract was best with 71.01 per
cent inhibition. Among the fungicides/chemicals mancozeb 0.2 per cent gave highest (76.19 per cent ) disease
control. Benefit cost ratio was also calculated on the basis of increase in yield over control and found that
mancozeb proved better. However , among the non-traditional chemicals neem leaf extracts or neem seed extracts
gave highest benefit cost ratio.
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Keywords
Diseases, Fungi, Onions, Biological phenomena, Fruits, Extraction, Plant extracts, Planting, Planting equipment, Pathogens