STUDIES ON SEEDLING BLIGHT OF CASTOR CAUSED BY Phytophthora nicotianae (=P. parasitica) (Dastur) Waterhouse
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Date
2015
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PROFESSOR JAYASHANKAR TELANGANA STATE AGRICULTURAL UNIVERSITY RAJENDRANAGAR, HYDERABAD
Abstract
A study was conducted on seedling blight of castor caused by Phytophthora nicotianae (=P. parasitica) at Department of Plant Pathology, College of Agriculture, Professor Jayashankar Telangana State Agriculture University, Rajendranagar, Hyderabad and Indian Institute of Oil Seed Research, Rajendranagar, Hyderabad. Nine pathogen isolates were collected from diseased castor seedlings, from different castor growing region of Telangana State, India and were designated as P1 to P9.
Pathogenicity of all the nine isolates was proved by Koch’s postulate of which isolate P3 was significantly virulent when compared to all other isolates.
Among the three media viz., carrot agar medium, corn meal agar medium and potato carrot agar medium, carrot agar medium showed greyish, white colour and fluffy to slight fluffy mycelium with good colony growth rate and mycelium abundance. Studies on morphological characteristics among nine isolates showed two types of sporangia and they differed as pear shape, papillate and globose, semipapillate sporangia.
Results of molecular polymorphism using RAPD markers indicated that there was no polymorphism among isolates. Based on cultural, morphological and molecular characters some variation among the isolates of Phytophthora nicotianae was observed.
Thirteen species of Trichoderma were isolated by serial dilution method from the rhizosphere of healthy seedlings of castor which were further used for biological control of seedling blight disease of castor. The Trichoderma isolates were checked along with 2 bioagents (Trichoderma harzianum 4d (Th4d) and Pseudomonas flurescence2 (Pf2) developed by IIOR). Trichoderma spp 6 (Trichoderma harzianum-6) was most effective in inhibiting the growth of pathogen under in vitro conditions followed by Pf2 and Th4d.
Seventeen castor varieties selected on the basis of their agronomical performance in the affected area viz. DCS-107, DCH-177, DCS-519, Kranti, Haritha, Kiran, PCH-111, PCH-222, JP-65, GCH-2, GCH-4, GCH-6, GCH-7, 3216-R, SH-72, DCS-78 and 48-1 were tested under glasshouse conditions for their response to per cent disease incidence against the P3 isolate of the Phytophthora nicotianae. Among them six varieties viz. PCH-222, GCH-2, GCH-4, GCH-6, GCH-7 and 3216-R were found resistant and remaining eleven varieties were susceptible to the pathogen.
Nine fungicide viz. Azoxystrobin, Dimethomorph, Mefenoxam + Mancozeb, Cymoxanil 8% + Mancozeb 64%, Trifloxystrobin 25% and Tebuconazole 50%, Thiophanate methyl 70% WP, Metalaxyl 35%WS, Mancozeb 75% WP and Copper oxychloride were screened at 0.1%, 0.2% and 0.3% concentrations against test pathogen of which two fungicide viz. Mefenoxam + Mancozeb and Metalaxyl 35%WS showed more than 90% inhibition of the pathogen at 0.1% concentration.
An experiment on integrated disease management of castor seedling blight disease was carried out in the green house by integrating the most potential bioagent Trichoderma harzianum-6 along with Trichoderma harzianum 4d (Th4d) and Pseudomonas fluorescence2 (Pf2) developed by IIOR, fungicide Mefenoxam + Mancozeb (0.1% ) using virulent isolate of Phytopthora nicotianae P3 in the susceptible variety of castor DCS 519. Among the treatments, seed treatment with Native Trichoderma isolate -T6 (2.6 ×106 spores/ml) + foliar application by Mefenoxam + Mancozeb (0.1%) was found to be most effective in reducing the disease incidence by 94.82% followed by seed treatment with Pf2 (IIOR) 1% + foliar application with Mefenoxam + Mancozeb (0.1%) (93.29%) when compared to control.