Studies On Collar Rot Of Okra Caused By Macrophomina Phaseolina( Tassi) goid
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Date
1996
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Birsa Agricultural University, Ranchi
Abstract
Okra (Abelmoschus esculentus (L.) Moench) suffers from collar rot a very destructive disease caused by Macrophonina phaseolina (Tassi) Gold (Rhizoctonia bataticola (Taub.) Briton-Jones). Disease incidence varied from 12.7 to 58.3% in different localities of Ranchi. The characteristic symptom of the disease was observed on both root and collar region of seedlings as well as adult plants.
The pathogen was isolated, Purified and identified by standard method. The pathogen satisfied koch's postulate tests.
Potato dextrose agar (solid) and Richards' (liquid) media supported maximum mycelial growth and sclerotial production. 6.5 pH was found to be optimum for mycelial growth and sclerotial production in Richards liquid medium.
All 13 plant species belonging to 6 families were infected during host range studies.
21 days old plant were highly susceptible to infection and older plants showed resistance to infection. High temperature, low rainfall and low humidity were favourable for disease development. Significantly negative correlations were established in between disease incidence and age of plants, average temperature, average relative humidity and rainfall. However, the disease incidence was positively correlated with average relative humidity and rainfall during 1995 only.
Late sowing minimized the disease development and gave good yield. In general, low disease incidence and higher yield were recorded during rainy season sown crop than summer season sown crop.
Okra varieties, Supriya (F), and Arka Anamika showed moderately resistant and tolerant reaction, respectively against disease.
The local isolate of Trichoderma viride showed maximum inhibition of mycelial growth of pathogen followed by T. harzianus (local isolate) and T. viride (Pantnager isolate) in vitro. All six isolates of three fungal antagonists inhibited cent per cent sclerotial production. Nature of mycoparasition was established.
Among different plant extracts, Bhangria leaf extract showed maximum inhibition of mycelial growth (32.6%) followed by Marigold (29.1%) and Karanj (26.1%) leaf extracts at 5 per cent concentration. Whereas at 10 percant concentration, Bharbhand leaf extract showed maximum inhibition of mycelial growth (45.0%) followed by Bhangria" (39.0%) and Marigold (34.4%) leaf extracts.