STUDIES ON DIVERSITY OF Sclerotium oryzae, Catt AND MANAGEMENT OF STEM ROT OF RICE
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Date
2019
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ACHARYA N G RANGA AGRICULTURAL UNIVERSITY, GUNTUR
Abstract
The stem rot of rice caused by Sclerotium oryzae (Catt.) is one of the major limiting factors for rice production in the Indian subcontinent. In an attempt to found the variability at cultural, morphological and genomic level and also to develop effective integrated management practices for rice stem rot, a total of twelve isolates of the pathogen and native bacterial biocontrol agents were collected from major rice growing areas of Andhra pradesh. The isolates of Sclerotium oryzae were designated as SOP1- SOP 12 whereas Pseudomonas fluorescens isolates designated as SOA- SOA-12.
Among the isolates of Sclerotium oryzae, Catt, cultural and morphological variability was assessed and by the utilisation of carbon resources on PDA, OMA and CZA media and by the mycelial growth rate on PDA. Among these media, PDA was well supported for growth compared with other media. Isolates were categorized into four groups, Group 1 with fastest growing, Group 2 with fast growing , Group 3 with medium growing and Group 4 with slow growing isolates based on time taken for 90mm diameter of mycelial formation on PDA. To know the polymorphism among the collected isolates of Sclerotium oryzae, Catt using RAPD analysis, primer survey was done with eight primers of OPA-2, OPA-3, OPA19, OPB-5, OPB-7, OPB-10, OPC-7 and OPC-10 for the amplification of DNA. Among them, OPB-5 and OPC-10 primers generated 17 percent polymorphism. The isolates of Pseudomonas fluorescens were screened against mycelial growth of Sclerotium oryzae with dual culture and significantly highest percentage of inhibition were noticed in SOA-10 with 97.44 % and lowest inhibition recorded in SOA-2 with inhibition of 37.56 %. Due to its high efficacy SOA-10 was selected for further studies.
A total of five fungicides viz., Hexaconazole, Difenoconazole, Tebuconazole, Trifloxystrobin + Tebuconazole, Pyraclostrobin and Krysoxim methyl of different concentrations in ppm were evaluated for their efficacy against mycelial growth and sclerotial viability of S. oryzae in rice system. Among them, difenconazole showed 100 percent highest inhibition and pyraclostrobin with least inhibition of 72.52 percent on mycelial growth. Incase of sclerotial viability difenconazole recorded highest inhibition and kresoxim methyl recorded least inhibition at different concentrations in minimum and maximum time intervals. The compatability between effective fungicide (difenconazole) and potential antagonist (SOA-10) revealed good compatability at lowest concentration (500 ppm).
During rabi 2018-19, field trial was conducted to evaluate the efficacy of effective fungicide and potential antagonist by artificial disease inoculation at late tillering stage. Different strategies were followed in the field, highest grain yield, straw yield and lowest PDI obtained in T6.
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D5872
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