Epidemiology of sclerotinia rot of Indian mustard
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Date
2009
Authors
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Journal ISSN
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Publisher
CCSHAU
Abstract
With a prime objective to investigate the role of environmental
factors in epidemiology of Sclerotnia rot of Indian mustard and to
diagnose the disease in field condition using spectral approach. Two
mustard varieties viz. RH 30 and Varuna were sown on four dates of
sowing last week of September, second week of October, last week of
October and second week of November during the rabi season 2008-09.
Disease incidence was recorded at weekly intervals after initiation of
disease in all the treatments. The weather data of the corresponding
periods were taken from the Agrimeterological. Observatory situated at
Research farm of the Chaudhary Charan Singh Haryana Agricultural
University, Hisar. The reflected radiance values in different IRs bands
were measured with the help of Ground Fruth Radiometer (GTR) over
crop surface in all the treatments under inoculated and uninoculated
sites from 10.00 a.m. to 12.00 noon. The reflectance values in all form
sands were also measured over Barium sulphate plate (100% reflection)
for using as standard reflectance values over a surface. The per cent
reflectance values were computed by taking the ratio of radiance value
over a crop surface and standard radiance value over a Barium
xii
sulphate plate. These spectral reflectance values in IRs bands were
used for computing spectral indices. Vegetation index, normalized
difference vegetation index, perpendicular vegetation index and disease
water stress indices on the same days of disease observations.
The maximum disease incidence was recorded in first date
of sowing and it decreased drastically with delay in sowings. The
maximum incidence in first date of sowing was 27.6 and 25.6 per cent
in mustard varieties RH-30 and Varuna, respectively. The weather
parameters : maximum temperature, minimum temperature, morning
relative humidity, evening relative humidity, sunshine hours and wind
speed were correlated with disease incidence by pooling the data first
for all the environments and then for both the varieties. The correlation
coefficients ranged from 0.17 to 0.78 in both the cultivars. The disease
incidence was directly associated with maximum temperature, morning
and evening relative humidity whereas, incase of sowing environments,
sunshine hours also played significant role in disease development. The
regression model based on significant weather parameters, explained
the variability in stem rot incidence upto 98 per cent, during different
sowing environments. The reflectance values were higher in visible
bands over healthy (uninoculated) crop in comparison to diseased
(inoculated) crop. The reverse trend was observed in case of infra red
reflectance over healthy and diseased crop surface. The vegetation
indices values were higher in healthy crop as compared to diseased
crop except disease water stress index-4. The correlation coefficients of
vegetation indices varied from -0.73 to -0.74 in RH-30 and from -0.75
to -0.79 in Varuna. The regression model based on significant
vegetation indices explained the variability in disease incidence upto 81
and 86 per cent in mustard varieties RH-30 and Varuna, respectively.
The spectral approach can be used as diagnostic tool for stem rot
incidence in mustard crop under field condition.
Description
Keywords
Diseases, Fungi, Mustard, Application methods, Sowing, Fruits, Crops, Biological phenomena, Planting, Relative humidity