Management of collar rot of cowpea caused by rhizoctonia solani kuhn using biofumigants
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Date
2017
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Department of Plant Pathology, College of Agriculture, Vellayani
Abstract
The study entitles “Management of collar rot of cowpea caused by Rhizoctonia solani kuhn using biofumigants” was undertaken in the Department of Plant Pathology, College of Agriculture, Vellayani during 2015-2017 with the objective to evaluate biofumigant nature of plants, plant oils and oil cakes against Rhizoctonia solani and to develop an ecofriendly management strategy for collar rot of cowpea using biofumigation.
The pathogen causing collar rot disease of cowpea was isolated from the infected cowpea plants collected from the Instructional Farm, College of Agriculture, Vellayani. Pathogenicity was confirmed, virulence rating was done and the collar rot isolate R1 was found to be the most virulent one. Based on morphological and cultural characteristics, the pathogen was identified as the Rhizoctonia solani kuhn (Accession no. EF429212). This was further confirmed using molecular identification by ITS sequencing and showed 100 per cent similarity with Thanatephorus cucumeris, the perfect stage of R. solani.
The antifungal and biofumigant action of ten different plants, four plant oils and four oil cakes/seed meals on mycelial growth of R.solani was evaluated under in vitro conditions in petridishes. Among these, incorporation of the leaf extracts of cabbage/ garlic creeper, lemongrass oil/ tea tree oil and mustard oil cake extract in PDA medium caused 100 per cent suppression of the pathogen. The invitro biofumigant activity of cabbage/cassava/garlic creeper/mustard, lemon grass oil/tea tree oil and the mustard oil cake was found to be statistically superior to all other treatements, and resulted in 100 per cent suppression of mycelial growth.
The biofumigant action of ten different plants, four plant oils and four oil cakes with biocidal principles was tested by subjecting the sclerotia of R.solani to biofumigant action under confined conditions in sealed containers. Biofumigation with plants, plant oils and oil cakes, in general, exerted suppression of mycelial regeneration from sclerotia. The extent of suppression was found to increase with increase with increase in period of incubation with the biofumigants. Cabbage, cassava, garlic creeper and mustard were found to completely suppress the regeneration of mycelial growth from the treated sclerotia. Biofumigation with lemongrass oil/ tea tree/ mustard oil cake resulted in 100 percent suppression of regeneration of mycelium. Accordingly, plants such as cabbage, cassava, garlic creeper and mustard, plant oils such as lemongrass oil and tea tree oil, oil cakes such as mustard and groundnut oil cake were selected for further in vivo studies.
An experiment was conducted under pot culture conditions to evaluate the efficacy of selected biofumigants involving 11 treatments and 5 replications in C.R.D. The treatments included the selected plants (50 g kg-1 soil), plant oils (5% soil drench) and oil cakes (10 g kg-1 soil) for suppression of collar rot of cowpea. The inoculated untreated control showed severe collar rot incidence (94.44%) compared to the treated pots. The maximum disease suppression (100%) was observed in cowpea plants grown on soil biofumigated with mustard plant/mustard oil cake which was on par with both chemical control check (0.1% carbendazim) and un-inoculated control. But the highest pod yield was recorded form plants grown on soil biofumigated with mustard oil cake (209.0 g) followed by treatment with mustard plant (185.4 g), which were significantly superior to the chemical control check (155.0 g) and un-inoculated control (143.0 g). These results revealed the enhanced effects of biofumigation for both disease suppression and growth enhancement.
The population of soil microflora exhibited a decrease in the biofumigated treatements and an increasing trend after raising the crop. Among the predominant saprophytic fungi obtained from biofumigated soil, the isolated F1 exhibited 47.44% and among the two bacterial isolates, the isolate B2 caused 44.44% inhibition of the pathogen.
The experiments revealed the scope of biofumigation for the management of R. solani under in vitro as well as in vivo. The collar rot caused by soil-brone pathogen, R. solani could be successfully managed by incorportation of either mustard plant (50g kg-1 soil) or tea tree oil (5% soil drench) or mustard/groundnut oilcake (10 g kg-1 soil)two weeks before raising cowpea.
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