PGPR: A novel strategy for the control of rice sheath blight disease

Authors: ZHOU, XIN-GIN - Texas A&M Agrilife; KUMAR, VIJAY - Auburn University; REDDY, MUNAGALA - Auburn University; KLOEPPER, JOSEPH - Auburn University; Jia, Yulin; ALLEN, THOMAS - Mississippi State Extension Service; WAY, MICHAEL - Texas A&M Agrilife

Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/3/2012
Publication Date: 2/27/2013
Citation: Zhou, X., Kumar, V.K., Reddy, M.S., Kloepper, J.W., Jia, Y., Allen, T.W., Way, M.O. 2013. PGPR: A novel strategy for the control of rice sheath blight disease. Thirty-Fourth Rice Technical Working Group Meeting Proceedings, Hot Springs, AR, February 27-March 1, 2012. Page 81.

Interpretive Summary:

Technical Abstract: Sheath blight caused by Rhizoctonia solani is the most important rice disease in Texas, Arkansas, Mississippi and other southern states. Due to the lack of sheath blight resistance in most commonly planted cultivars, southern rice famers apply more than 1 million pounds of fungicides annually to control diseases of rice, primarily for sheath blight control. Rice farmers are in need of the development of alternative or complementary management options to reduce their heavy reliance on fungicides. The combination of biocontrol agents with reduced rates of fungicides may afford protection equivalent to that obtained with full rates of fungicides. The results of our previous studies indicate that the Bacillus subtilis Plant Growth-Promoting Rhizobacteria (PGPR) strain MBI-600 was effective in suppressing sheath blight and was compatible or tolerant to azoxystrobin and other fungicides commonly used for sheath blight management. MBI-600 is an active ingredient in the biofungicide Integral (registered trademark). Azoxystrobin is the commonly used fungicide for control of sheath blight in rice. The objectives of this study were to determine the optimum rates of combined use of the biocontrol agent with azoxystrobin under greenhouse conditions and to evaluate efficacy of their combined use for sheath blight control and yield increase in the field. A greenhouse experiment was conducted as a 5 × 7 factorial with five concentrations of MBI-600 (0, 10**3, 10**6, 10**9 and 10**11 CFU/ml) and seven rates of azoxystrobin [0, 17, 33, 50, 67, 83, and 100% of the recommended rate (0.16 kg a.i./ha)]. Seeds of variety Cocodrie were treated with MBI-600 at aforementioned concentrations and were air-dried prior to seeding. At the 3-leaf stage, plants were sprayed with MBI 600 and azoxystrobin (Quadris 2.08 SC) at different concentrations. After 24 h, sclerotia of R. solani were inoculated at the base of treated seedlings near the soil line. Inoculated seedlings were covered with transparent soft drink bottles for maintaining inside moisture. Applications of MBI-600 at 10**9and 10**11 CFU/ml were effective in reducing disease severity with the later concentration completely eliminating the disease. Sheath blight severity was reduced with applications of azoxystrobin at 67, 83, and 100% of the recommended rate. The optimum rates of MBI-600 and azoxystrobin for combined use to achieve maximum sheath blight control were 10**9 CFU/ml and 50% of the recommended rate, respectively. A dose response model describing the efficacy of combined use of MBI-600 with azoxystrobin for sheath blight reduction was developed. A field trial was conducted in 2010 and 2011 at Beaumont, Texas. R. solani inoculum was introduced into each plot measuring 5.4 m long and 1.2 m wide, at panicle differentiation. MBI-600 was applied to seed prior to planting and the foliage at 10**9 CFU/ml at the boot stage. Foliar applications of azoxystrobin at 0.08 or 0.16 kg a.i./ha were made at the boot stage. Two additional combined treatments of MBI-600 with azoxystrobin at either rate as well as an untreated control were included for each trial. In each year, applications of MBI-600 resulted in a significant reduction in sheath blight severity over the untreated control. The combined use of MBI-600 with azoxystrobin at 0.08 kg a.i./ha further reduced disease severity. The efficacy of this combined treatment was comparable to that of azoxystrobin at 0.16 kg a.i./ha (the full recommended rate). The combined treatment tended to have higher grain yield than the untreated control and have similar yield to azoxystrobin at 0.16 kg a.i./ha. In summary, the combined use of the biocontrol agent with a reduced rate of fungicide shows promise as a novel practical means to minimize yield losses caused by sheath blight while reducing fungicide use on rice by 50%. This research