Effect of abiotic factors on incidence of Sclerotinia rot on Indian mustard

摘要

Rot of Indian mustard (Brassicajuncea) caused by Sclerotinia sclerotiorum (Lib.) de Bary has become important in recent times in India and elsewhere with high disease incidence and severe yield losses leading to discouragement of growers of the crop.The pathogen is reported to infect about 400 plant species with no proven source of resistance against the disease reported till date in any of the hosts. An experiment was laid out at farm of the Centre [77°27'E, 27°12'N, 160 m above mean sea level, deep loamy alluvium derived soil with pH 8.0] in plots of 5 m×4.8 m with 30 cm×l0 cm spacing in randomised block design with four replications and three dates of sowing (07, 28 Oct, 18 Nov 2005) using the test variety Rohini to understand the effect of different abiotic factors on incidence of the disease. Soil moisture data was recorded at weekly intervals from each plot by gravimetric method. Collecting petals during flowering period daily between 0800-1000 hrs and placing them on chloramphenicol amended potato dextrose agar medium recorded infestation of Indian mustard petals by spores of S. sclerotiorum. Weather parameters, viz,maximum and minimum temperature, morning and aftemoon relative humidity, bright sunshine hours were recorded at a meteorological observatory about 200 m from the site of experimentation. Analysis of data indicated that the petal infestation by pathogen spores was positively related (R2: 0.97) with increase in bright sunshine hours. Incidence of Sclerotinia rot was positively correlated with increase in soil moisture content (R2: 0.84), particularly during the flowering period and more specifically between 50 and 60 days after sowing. Combination of clear sky with cool weather and high soil moisture during the critical stage of 50-60 day age of crop seems to have favoured higher Sclerotinia rot incidence on Indian mustard at the site of experimentation.