Eco-friendly management of Sclerotinia rot disease of oilseed brassica
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Date
2017
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Dr. Rajendra Prasad Central Agricultural University, Pusa (Samastipur)
Abstract
The oil yielding Brassica crops grown in India include rai or raya or mustard [Brassica juncea (L.) Czern. & Coss.], and rapeseed (B. rapa sp. oleifera). Sclerotinia rot disease of oilseed brassica incited by Sclerotinia sclerotiorum (Lib.) de Bary is the most ubiquitous, omnivorous, soil-borne and destructive plant pathogen distributed worldwide.
Survey conducted at different locations showed its prevalence in Bihar with variable magnitude of incidence ranging from 25 to 47 per cent.
Symptom first appeared on the leaf as water soaked spot then whole leaf got water soaked followed by drooping and hanging in air, the leaves showed blighting then ultimately dried. On the stem, first symptom of Sclerotinia rot was noticed as water soaked patches which soon turned into whitish brown, enlarged and finally girdled the stem completely. The pith of stem became hollow in which irregular sized sclerotia were observed.
Isolation of the pathogen was made on PDA medium and identified as Sclerotinia sclerotiorum (Lib.) de Bary. The fungus produced aerial mycelium, which was hyaline, branched well developed and appeared cottony with closely septate hyphae. The hyphae were 2.0-11.5 µm in width and contained dense granular protoplasm. The sclerotia were round to irregular in shape in culture and measured 1.5-7 mm in width and 2-15 mm in length. Apothecia were brown in colour and were round to globose type, measured 5-21 mm in length, 2-9 mm in diameter and 0-7 numbers arose from single sclerotium. The pathogenic behaviour of the fungus was also confirmed after test.
Potato dextrose agar (PDA) medium among solid media and Richards’ medium among liquid medium were found most supportive for the growth and sclerotial formation of the Sclerotinia sclerotiorum.
Temperature 20-25⁰C and pH 4.5 to 5.5 are most suitable for the growth and sclerotial formation of Sclerotinia sclerotiorum.
Out of ten entries, NDN-16-79 were found to be resistant against Sclerotinia rot disease. NDN-16-75, NDN-16-76, NDN-16-77 and NDN-16-81 were moderately resistant (MR).
Highest seed yield of 1290 kg/ha was recorded when crop was sown timely on 30th October. Multiple regression between per cent disease incidence and weather variables indicated that the combined effect of different weather variables favoured the disease development causing up to 86 per cent variation in the Sclerotinia rot incidence.
In management trial, the crop sown on 30th October recorded significantly higher yield, 1000 seed weight, stem diameter and lower disease incidence and intensity than early as well as late sown crop.
Variety ‘Rohini’ recorded lower disease incidence, disease intensity, lesion length of the disease and recorded significantly greater stem diameter, 1000 seed weight and seed yield as compared to yellow sarson variety, 66-197-3.
Seed treatment with carbendazim + foliar spray of carbendazim recorded lowest disease incidence, disease intensity and shortest lesion length of the diseased plants and highest stem diameter, 1000 seed weight, seed yield and highest (8.82) incremental benefit-cost ratio. This treatment was found best for the management of Sclerotinia rot of oilseed brassica.
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