Novel Strategies for Managing Blast Diseases on Rice and Wheat
Rice blast, caused by the Magnaporthe oryzae Oryza pathotype remains an explosive threat to U.S. rice. High-yielding rice varieties preferred by farmers are often classified as "susceptible" or "highly susceptible" to blast, adding costs ranging from $4.75 to $20.87 per acre. Host resistance is one of the most effective means of control, but there is a critical need for efficient strategies to move resistance genes into elite rice varieties while maintaining yield and quality. In contrast for the newly-emerged wheat blast disease in South America (S.A.) caused by the M. oryzae Triticum pathotype, few resistance genes have been identified in wheat and fungicide treatments are unreliable. It is paramount to prepare for incursion and prevent establishment of the S.A. fungus on U.S. wheat. It is also essential to determine the potential for blast to emerge and establish in the U.S. wheat crop from native strains of the Lolium pathotype, which currently cause gray leaf spot disease on turf grasses. Turf grass strains infect wheat grown under greenhouse conditions and a native Lolium strain was isolated from a single severely-blasted wheat head in Kentucky in 2011. Therefore, wheat blast could establish in the U.S. by introduction of aggressive strains endemic to S.A., or by emergence of a native Lolium strain shifting to become an aggressive wheat pathogen in the field. The major premise for this proposal is that various diseases caused by host-differentiated M. oryzae populations can be viewed as a single system for developing novel control strategies, and that extensive research into disease on one host can aid in control on others. For example, pathogenicity factors and avirulence (Avr) effectors have been extensively characterized from rice pathogens, and 18 blast resistance genes have been cloned from rice. Our goal is to apply this knowledge to develop new genetic tools for controlling rice blast and preventing wheat blast in the U.S. Specific objectives are to: (1) enhance blast resistance in elite US rice varieties; (2) develop a novel strategy using host-induced gene silencing (HIGS) for controlling blast; (3) control wheat blast through the understanding of wheat blast genetics and genomics, pathology, ecology and epidemiology; (4) incorporate blast resistance into wheat; (5) develop and validate forecasting models for rice and wheat blast; (6) assess consumer attitudes and economics of cisgenic blast-resistant rice; (7) disseminate results through educational resources and programs for stakeholders; and (8) attract a new generation of plant pathologists to work on plant biosecurity. Outputs from this project will include efficient cisgenic strategies for incorporating resistance genes into high-yielding U.S. varieties, and pathogen population analysis to inform breeders' resistance gene choices. Understanding wheat blast field biology together with effective diagnostics, workshops and training resources will underpin a first-responder network for preventing establishment of wheat blast in the U.S. Deploying forecasting models and assessing economic and social impacts of new technologies will benefit both rice and wheat production.
This project involves collaborators with expertise in pathogen population dynamics, epidemiology, genetics, genomics, plant transformation, forecast modeling, extension, education and economics. Aspects of this project continue from previous NIFA support (grant # 2009-55605-05201). Major methods for each objective are summarized. (1) Enhance blast resistance in elite U.S. rice varieties. To simplify the regulatory process, cisgenic approaches (only rice sequences are retained in the new variety) will be developed to introduce cloned rice resistance genes into preferred rice varieties. To guide resistance gene deployment, Avr-effector compositions in extant blast populations will be assessed through sequencing of pooled, barcoded PCR samples. (2) Develop host-induced gene silencing (HIGS) for controlling blast. HIGS would control blast disease by silencing fungal genes needed for disease, through expressing siRNAs targeted against these fungal genes directly in rice. If effective, HIGS has the potential to exploit the wealth of fungal pathogenicity genes previously identified through foundational research. (3) Wheat blast control through understanding wheat blast genetics, pathology, ecology and epidemiology. We will focus on understanding the population structure, ecology and epidemiology of the wheat blast fungus in S.A., on determining the potential for native Lolium strains to establish on U.S. wheat, and on validating, refining and deploying PCR-based diagnostic protocol(s). (4) Incorporate blast resistance into wheat. We previously identified some U.S. wheat varieties with high levels of resistance to some wheat blast strains in growth chamber and greenhouse studies. Broadly useful resistance genes will be confirmed through field tests in S.A. Molecular markers will be developed for incorporating at least one effective resistance gene into wheat. We will also test if cloned rice resistance genes function to control blast after transformation into wheat. (5) Develop and test forecasting models for rice and wheat blast. Models will be developed based on both regional-scale, climate indices and local-scale weather, and validated for rice in the U.S. and for wheat in S.A. (6) Assess consumer attitudes and economics of cisgenic rice by implementing "willingness to pay (WTP)" surveys with participants in the U.S. and Belgium. Results will be broadly communicated in order to promote acceptance of cisgenics throughout the rice production and marketing chain. Analysis of the economic impact of cisgenic resistance and blast forecasting will also promote acceptance. (7) Disseminate results through educational resources and programs for stakeholders through rice blast training workshops in the U.S., wheat blast training workshops in the U.S. and in South America, extension publications and apps for mobile devices, and international educational outreach. (8) Attract a new generation of plant pathologists to work on international plant biosecurity. We will engage undergraduates in workshops focused on wheat production, policy and pathogens, on plant biosecurity and containment research, and on rice and the global importance of food security.
Rice and wheat are the top two sources of calories in the human diet, and both are important export crops for the U.S. Rice blast disease, caused by the fungus Magnaporthe oryzae remains an explosive threat to rice production in the U.S. and globally. Since 1985 when M. oryzae first appeared on wheat in Brazil, blast has become a major constraint to wheat production in several South American countries. It is critical to prevent establishment of wheat blast in the U.S. Disease control is complicated by the lack of a clear understanding of how the disease develops and spreads in the field, by extreme variability shown by the fungus and by unknowns associated with climate change. We will apply knowledge gained through previous research and cloned blast resistance genes for disease control, including developing methods for choosing effective resistance genes and rapidly deploying them, methods for forecasting disease risk and informing farmers of the best control options, and novel methods to control disease by turning off fungal genes needed for disease. Although genetic resistance is the most effective way to control blast diseases, high-yielding rice varieties preferred by U.S. farmers generally lack resistance. These varieties require expensive fungicide applications when weather conditions favor disease. There is urgent need for efficient strategies to move new resistance (R) genes into elite rice varieties while maintaining yield and quality. We will develop cisgenic technology, in which only rice DNA sequences are introduced, to precisely incorporate resistance genes into elite rice varieties. Adoption of cisgenic rice by U.S. farmers requires consumer acceptance in the U.S. as well as in Europe and other import markets. We will assess consumer attitudes in the U.S. and Europe toward cisgenic rice, as compared to transgenic rice in which some non-rice DNA sequences are also introduced. Strategies for promoting consumer acceptance will be developed based on this assessment. In contrast, few wheat blast resistance genes have been identified. We address this with strategies to identify wheat resistance genes through field tests of U.S. wheat varieties against native pathogen populations in South America. We will also test if moving rice resistance genes into wheat will provide effective wheat blast resistance. Development and use of a blast forecasting model will inform farmers if and when they need to apply fungicides, and will warn first responders when the weather is right for wheat blast disease to occur. Understanding wheat blast biology and training a first-responder network will enable rapid detection and response to any wheat blast outbreaks in the U.S. We will also develop novel strategies for blast control based on designing plants that block the fungus from expressing genes it needs to cause disease. Our extension programs will produce publications and workshops to inform extension specialists, farmers and other first responders about wheat blast and the novel disease management strategies. We will design and implement educational activities to attract undergraduate students to careers in plant pathology and in plant biosecurity.