Evaluation of Rhizosphere-Associated Microbial Antagonists against Sheath rot (Sarocladium oryzae) of Rice

Sheath rot (ShR) of rice, caused by Sarocladium oryzae (Sawada) Gams and Hawks, is a significant seed-borne disease found in all rice-growing countries worldwide. Fungicides are employed to regulate ShR, although these chemical techniques are neither economically nor environmentally sustainable. To develop new biological control agents for the management of ShR, twelve Trichoderma sp. and twenty Bacillus sp. isolated from rhizospheric soils of cowpea, soybean, and rice plants in the field were initially screened in the laboratory based on their antagonistic activities against Sarocladium oryzae using plate assays that show fungal pathogen growth inhibition. Among the twenty Bacillus isolates, only nine isolates were confirmed to have anti microbial activities by forming the inhibition zones varying from 8- 14.60 mm. Bacillus isolate 6 was to be found most effective with maximum inhibition zone of 14.60 mm which was followed by Bacillus isolate 12 (12.00mm) and Bacillus isolate 14 (10.30mm), but the rest twelve Bacillus isolates did not reproduce any observable inhibition zone against S oryzae. The observed inhibition zone proves the antagonistic effect of Bacillus isolates is mainly due to production of antibiotic compounds. All the twelve Trichoderma isolates showed in vitro inhibitory effect on Sarocladium oryzae in volatile compounds assay ranging from 2.60% to 35.11%. After 8 days of incubation, Trichoderma isolate 2 exhibited maximum mycelial growth of 35.11% followed by Trichoderma isolate 9 (27.20%) and Trichoderma isolate 1(26.45%). These antagonistic Trichoderma and Bacillus isolates significantly suppressed the disease development of sheath rot pathogen in an in vitro condition, suggesting that they can be potential biological control agents for the seed borne rice diseases.