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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Developing biologically Based Management Strategies for Integrated Control of Sheath Blight in Southern Rice

Project Director (PD): Xin-Gen Zhou [1]

Lead State: TX Lead Organization: Texas AgriLife Extension

Cooperating State(s): Alabama, Mississippi

Undesignated Funding: $185,928

Start Date: Oct-15-2010 End Date: Oct-14-2013

Summary: This is a four state collaboration research project. Over 75% of rice production in the U. S. occurs in the South, and Arkansas, Mississippi and Texas are among the leading producers with a value of $ 2 billion annually. Sheath blight is the most serious disease, causing millions of dollars of losses annually. Ratoon (second) crop producers have no labeled fungicides for use and suffer heavy yield losses. None of the leading high yielding cultivars have acceptable levels of resistance. Growers mostly rely on fungicides and apply 1 million pounds of them annually to rice, costing growers 26 million dollars a year for control of diseases, primarily for sheath blight control. Continual, extensive use of fungicides makes existing disease management practices unaffordable and non-sustainable. Rice producers, especially ratoon crop producers, are in urgent need of sustainable and environmentally-friendly management alternatives. Brassica cover cropping and biocontrol bacterial agents have demonstrated ability to suppress sheath blight in our research and offer a new potential for managing this disease. Brassica crops produce chemicals toxic to the sheath blight pathogen and reduce primary inoculum in soil by the process of biofumigation. The overall objective of this project is to develop novel, biologically-based management strategies for integrated control of sheath blight by using brassica biofumigation cover crops and biocontrol bacterial agents combined with reduced fungicide rates and partially resistant cultivars. This program will provide new disease management tools for rice producers in the South while reducing use of fungicides by more than 50%. Objectives: 1. Screen for promising brassica biofumigation crops in the greenhouse. (Year 1 in Texas, Arkansas and Mississippi) 2. Evaluate the efficacy of use of antagonistic bacteria in combinations with reduced fungicide rates to suppress sheath blight in the greenhouse. (Year 1 in Texas, Alabama and Mississippi) 3. Evaluate the efficacy of integrating biofumigation cover crop, biocontrol agent, rate reduced fungicide, and partial resistant cultivar to control sheath blight on main and ratoon (second) crops in the field. (Years 2 and 3 in Texas, Arkansas and Mississippi). 4. Disseminate the results of research and new management options for sheath blight to rice producers and other clientele. (Year 3 in Texas, Arkansas and Mississippi).

Final Report:

Results From report submitted by the PI to USDA CRIS report system PROGRESS: 2010/09 TO 2011/08 OUTPUTS: A series of in vitro, greenhouse and field evaluations were conducted to identify the plant growth-promoting rhizobacteria (PGPR) and the brassica crops that are most effective in suppressing sheath blight caused by Rhizoctonia solani in rice. More than 70 PGPR strains that were previously demonstrated growth promotion in other plants and antibiosis against other plant pathogens were screened for their antagonistic activity on mycelial growth of R. solani, germination of sclerotia and hyphal growth of germinated sclerotia on agar plates. They were also examined for their ability to inhibit lesion development on detached leaf blades of rice and to enhance vigor of seedlings. Twenty PGPR strains that performed well in these tests were selected and evaluated for suppressing sheath blight in rice seedlings in the greenhouse. One Bacillus subtilis strain, MBI600, was among the most effective PGPR strains screened. MBI600 was evaluated for its potential mechanisms involved in disease suppression and its growth promoting activity on four rice cultivars. MBI600 also was evaluated for its compatibility with eight commonly-used fungicides at the concentrations of 100 to 1,000 ppm. MBI600 and its combined use with azoxystrobin at different rates were further determined in rice seedlings under greenhouse conditions to develop a dose response curve that can determine the optimum concentrations of MBI600 and azoxystrobin for control of sheath blight. Thirty-seven brassica species and other related plants were evaluated on agar plates for their volatile antagonistic activity on mycelial growth of R. solani. Ten brassica species that significantly inhibited the pathogen in the evaluations were further tested for their ability to reduce the populations of R. solani and disease severity in soils from AR, MS and TX. Mustard cv. Caliente 199 that was shown to be among the most effective brassica species in these tests was selected to determine for an amended rate response curve. Field observations and trials were conducted to determine the optimum times for seeding and incorporating mustard cv. Caliente 199 in TX, AR and MS. Three dates for seeding the brassica in the fall and winter of 2010 and two dates for seeding the brassica in the spring of 2011 were conducted in TX. The activities and part of the results of this research project were timely delivered to rice producers, crop consultants, county extension agents, chemical industry, academic societies and the general public through annual Beaumont and Eagle Lake field days, Texas Rice Festival, Southeast Texas Rice Symposium, Texas Department of Agriculture pest inspection personnel training, Annual meeting of the American Phytopathological Society, Proceedings of 2nd Asian PGPR Conference, U.S. Rice Breeding Conference, and publications of outreach and professional newsletters and scientific journals. PARTICIPANTS: Kuma, K.V.K. actively participated in the research activities of this project. He conducted lab and greenhouse evaluations screening for effective biocontrol agents and their combined use with fungicides during his PhD research program at the Department of Entomology and Plant Pathology, Auburn University, Auburn, AL. Dr. Kumar now is a faculty member of the Acharya N G Ranga Agricultural University, Hyderabad, India. This project partially trained two PhD graduate students, one undergraduate student and one postdoctoral researcher. TARGET AUDIENCES: The activities and part of the results of this research project served more than 750 persons including rice farmers, crop consultants, county extension agents, chemical industry representatives, other professionals and the general public through annual field days, Texas Rice Festival, Southeast Texas Rice Symposium,and Texas Department of Agriculture pest inspection personnel training. The results of this research also were timely delivered to national and international academic societies through the Annual meeting of the American Phytopathological Society, Proceedings of 2nd Asian PGPR Conference, U.S. Rice Breeding Conference, and publications of professional newsletters and scientific journals. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period. IMPACT: 2010/09 TO 2011/08 The B. subtilis PGPR strain MBI600 was identified as the most promising biocontrol agent for control of rice sheath blight. MBI600 was one of the screened PGPR strains that showed greatest ability to inhibit vegetative growth and germination of sclerotia of R. solani and reduce disease severity in the detached leaf and greenhouse-grown seedling bioassays. These biocontrol effects are primarily involved in the production of siderophores (low molecular weight iron-chelating compounds) by MBI600, an effective antibiosis mechanism against R. solani and many other plant pathogens. Seed treatment with this bacterial strain at 106 CFU/ml or above significantly improved seed emergence and promoted plant growth of four rice cultivars (Cocodrie, Catahoula, Neptune and Trenasse). MBI600 was compatible with fungicides commonly used for rice sheath blight management. The strain had strongly tolerance to benomyl, hexaconazole, mancozeb, propiconazole, tricyclazole and validamycin, and good tolerance to azoxystrobin and carbendazim. A dose response curve that adequately described efficacy of combined use of MBI600 and azoxystrobin for sheath blight reduction was developed from greenhouse bioassays. MBI600 at 109 CFU/ml when used in combination with azoxystrobin at 50% or above of the recommended rate (0.18 kg a.i./ha) completely controlled sheath blight. MBI600 at 109 CFU/ml in combined use with azoxystrobin at 50% of the recommended rate thus is selected as the optimum combination for future field evaluations. Mustard cv. Caliente 199 was identified as the most promising brassica crop that was effective in inhibiting growth of R. solani and reducing soil populations of the fungus in the lab and greenhouse bioassays. Based on field observations and the results of field trials, optimum dates to seed mustard cv. Caliente 199 were in early to middle October in TX, and in late September to early October in AR and MS. Seeding rates could range from 5.5 to 11 kg/ha. The brassica crop could be plowed into soil before winterkill. In conclusion, we have successfully identified the best performing biocontrol agent and its combined use with a dose-reduced fungicide as well as the effective brassica crop that can be used in TX, AR and MS in year 1 of this project. The performance of these three disease control components for disease control and yield increase will be evaluated under field conditions in TX, AR and MS in year 2 of this project. The new rice sheath blight management strategies developed from this project have the high potential of being directly adopted for rice production in the South. Both the biocontrol agent MBI600, the active ingredient in the biopesticide Integral, and the biofumigant brassica cover crop cv. Caliente 199 are commercially available products.

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system The B. subtilis PGPR strain MBI600 was identified as the most promising biocontrol agent for control of rice sheath blight. MBI600 was one of the screened PGPR strains that showed greatest ability to inhibit vegetative growth and germination of sclerotia of R. solani and reduce disease severity in the detached leaf and greenhouse-grown seedling bioassays. These biocontrol effects are primarily involved in the production of siderophores (low molecular weight iron-chelating compounds) by MBI600, an effective antibiosis mechanism against R. solani and many other plant pathogens. Seed treatment with this bacterial strain at 106 CFU/ml or above significantly improved seed emergence and promoted plant growth of four rice cultivars (Cocodrie, Catahoula, Neptune and Trenasse). MBI600 was compatible with fungicides commonly used for rice sheath blight management. The strain had strongly tolerance to benomyl, hexaconazole, mancozeb, propiconazole, tricyclazole and validamycin, and good tolerance to azoxystrobin and carbendazim. A dose response curve that adequately described efficacy of combined use of MBI600 and azoxystrobin for sheath blight reduction was developed from greenhouse bioassays. MBI600 at 109 CFU/ml when used in combination with azoxystrobin at 50% or above of the recommended rate (0.18 kg a.i./ha) completely controlled sheath blight. MBI600 at 109 CFU/ml in combined use with azoxystrobin at 50% of the recommended rate thus is selected as the optimum combination for future field evaluations. Mustard cv. Caliente 199 was identified as the most promising brassica crop that was effective in inhibiting growth of R. solani and reducing soil populations of the fungus in the lab and greenhouse bioassays. Based on field observations and the results of field trials, optimum dates to seed mustard cv. Caliente 199 were in early to middle October in TX, and in late September to early October in AR and MS. Seeding rates could range from 5.5 to 11 kg/ha. The brassica crop could be plowed into soil before winterkill. In conclusion, we have successfully identified the best performing biocontrol agent and its combined use with a dose-reduced fungicide as well as the effective brassica crop that can be used in TX, AR and MS in year 1 of this project. The performance of these three disease control components for disease control and yield increase will be evaluated under field conditions in TX, AR and MS in year 2 of this project. The new rice sheath blight management strategies developed from this project have the high potential of being directly adopted for rice production in the South. Both the biocontrol agent MBI600, the active ingredient in the biopesticide Integral, and the biofumigant brassica cover crop cv. Caliente 199 are commercially available products.

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