Abstract
Field experiments were undertaken to determine the effect of sowing dates and weather parameters on the disease progression or severity of Alternaria blight of rapeseed mustard and their impact on yield for the two consecutive years 2008-2009 and 2009-2010. Disease severity gradually increased with delay in sowing irrespective of three different varieties (Binoy, Seeta and Bhagirathi). The crop sowing from 20th October to 5th November recorded significantly less disease severity with the highest seed yield irrespective of varieties and enhanced in subsequent sowing dates. Bhagirathi showed significantly less disease severity with maximum yield followed by Binoy and Seeta on leaf and siliqua infection on all sowing dates. 90 days old plants showed highest disease severity. From 20th October to 5th November, sowing only minimum temperature (9.69 to 12.04°C) had significant negative correlation, while minimum relative humidity (44.9 to 60.2% RH), wind velocity (during morning) (0.55 km to 1.04 km/h.) and total rainfall (5.74 mm) had positive significant correlation with disease progression upto 59%. Whereas in 20th November sowing minimum temperature (9.69 to 15.74°C, minimum(39 to 88%) and maximum (96 to 99%) relative humidity, wind velocity (during morning)(0.4 to 1.29 km/h), bright sunshine hours (3.8 to 9.0 h) and total rainfall (69.6 mm) had positive significant correlation and vapour pressure (noon, morning)(9.7-29.2 mb and 9.2-14.2 mb respectively), wind velocity (evening) (0.4 to 1.3 km/h) had negative significant correlation on disease progression upto 62%. In 5th December sowing, vapour pressure (noon)(9.7 to 17.5 mb), bright sunshine hours (3.8 to 9.2 h), total rainfall (73.7 mm) and minimum temperature(9.7-18.2°C) had positive significant correlation on disease progression upto 73%. In the West Bengal condition the suitable sowing date of mustard will be last week of October with tolerant variety Bagirathi could be cultivated to avoid loss from Alterania blight and increase the seed yield. Key words: Alternaria blight, mustard, sowing date, variety, weather, yield.
Highlights
Indian mustard (Brassica juncea) is widely cultivated in Indian sub-continent because of its relative tolerance to biotic and abiotic stresses and inherent high yield potential
Amongst the major constraints in releasing higher yields, the disease likes Alternaria blight incited by Alternaria brassicae (Berk & Sacc.) is one of the most widespread and destructive disease throughout India causing 35 to 40% yield losses (Kolte et al, 1987)
The four dates of sowing were considered as main plots and within such a main plot the three cultivars were treated as sub plots
Summary
Indian mustard (Brassica juncea) is widely cultivated in Indian sub-continent because of its relative tolerance to biotic and abiotic stresses and inherent high yield potential. Significant effect of sowing dates in both the years of experimentation on Alternaria leaf blight severity and area under disease progress curve was noticed Among the three cultivars tested Seeta sown on all dates showed significantly more disease severity of leaf, siliqua infection and number of spots per siliqua followed by
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