|Kumar, K. Vijay Krishn|
Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 6/1/2011
Publication Date: 6/15/2011
Citation: Zhou, X., Kumar, K.A., Reddy, M.S., Liu, G., Kloepper, J.W., Jia, Y., Allen, T.W., Lu, S. 2011. Biocontrol-based sheath blight management to reduce fungicide use on rice. Texas Rice Special Section, Highlighting Research in 2011. p. XXIV-XXV. Interpretive Summary:
Technical Abstract: Sheath blight (ShB) caused by Rhizoctonia solani is one of the most important rice diseases in Texas, Arkansas, Mississippi, and other southern states. The lack of complete ShB resistance in the most commonly planted varieties and the severity of this disease results in southern U.S. rice farmers applying more than 1 million pounds of fungicides annually. Hence, there is an urgent need to develop alternative or complementary management options. Combined use of biocontrol agents with reduced rate fungicides can be a viable solution toward this goal. The results of our previous studies suggest that the Bacillus subtilis strain MBI-600 was effective in suppressing ShB and was compatible or tolerant to azoxystrobin and other fungicides. Azoxystrobin is one of the most effective and commonly used fungicides for control of ShB. The objectives of the present study were to determine the optimum rates of combined application of the biocontrol agent and azoxystrobin under greenhouse conditions, and evaluate their efficacy for ShB control and impact on yield in the field. A greenhouse experiment was conducted as a 5 x 7 factorial with 5 concentrations of MBI-600 (0, 103, 106, 109 and 1011 CFU/ml) and 7 rates of azoxystrobin (0, 17, 33, 50, 67, 83 and 100% of the full recommended rate). Sclerotia of R. solani were placed on the sheaths of treated plants. Applications of MBI-600 at 109 and 1011 CFU/ml to both seeds and plants at the 3-leaf stage were effective in reducing disease severity, with the highest concentration completely eliminating the disease. ShB severity was significantly reduced with applications of azoxystrobin at 67, 83, and 100% of the full recommended rate to 3-leaf plants. The optimum rates of MBI-600 and azoxystrobin for combined application to achieve maximum ShB control were 109 CFU/ml and 50% of the recommended rate, respectively. A field trial was conducted in Texas with R. solani inoculum introduced into plots at the time of panicle differentiation. MBI-600 was applied as a seed treatment and as a foliar spray, while azoxystrobin was applied as a foliar spray only. Foliar applications of MBI-600 and azoxystrobin (Quadris 2.08 SC) individually and in combination were made at the boot stage. MBI-600, applied to both seed and to foliage at 109 CFU/ml, resulted in a significant reduction in ShB severity over the untreated control. The combined use of MBI-600 with azoxystrobin at 4.5 fl oz/A further reduced disease severity. The efficacy of this combined treatment was comparable to that of azoxystrobin at 9.0 fl oz/A (the full recommended rate). The combined treatment tended to have higher grain yield than the untreated control and have similar yield to azoxystrobin at 9.0 fl oz/A. The combined use of the biocontrol agent with a reduced rate fungicide may provide a practical means to minimize yield losses caused by ShB, while reducing 50 percent of fungicides use on rice.