Recovery plan for wheat blast caused by Magnaporthe oryzae pathotype Triticum

Authors: VALENT, BARBARA - Kansas State University; CRUPPE, GIOVANA - Kansas State University; STACK, JAMES - Kansas State University; CRUZ, CHRISTIAN - Purdue University; FARMAN, MARK - University Of Kentucky; PAUL, PIERCE - The Ohio State University; Peterson, Gary; Pedley, Kerry

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2021
Publication Date: 7/13/2021
Citation: Valent, B., Cruppe, G., Stack, J.P., Cruz, C.D., Farman, M.L., Paul, P.A., Peterson, G.L., Pedley, K.F. 2021. Recovery plan for wheat blast caused by Magnaporthe oryzae pathotype Triticum. Plant Health Progress. 22:182-212. https://doi.org/10.1094/PHP-11-20-0101-RP.
DOI: https://doi.org/10.1094/PHP-11-20-0101-RP

Interpretive Summary: The wheat blast recovery plan is one of several disease-specific documents produced as part of the National Plant Disease Recovery System (NPDRS) called for by Homeland Security Presidential Directive Number 9 (HSPD-9). The purpose of the NPDRS is to ensure awareness and availability of tools, infrastructure, communication networks, and capacity required to mitigate the impacts of high consequence plant disease outbreaks and sustain crop production at levels that meet national needs. Each disease-specific plan is intended to provide a brief primer on the disease and the threat it presents, assess the status of critical recovery components, and identify needs for disease management research, extension, and education. These recovery plans are not intended to be stand-alone manuals that address all of the many and varied aspects of plant disease outbreaks and all of the decisions that must be made and actions taken to achieve effective response and recovery. They are, however, documents that will enable USDA to guide further efforts directed toward plant disease recovery.

Technical Abstract: Wheat blast is an explosive new fungal disease of wheat caused by an Magnaporthe oryzae (synonym of Pyricularia oryzae) host-adapted subpopulation, known as the M. oryzae Triticum pathotype (MoT). Strains of the MoT pathotype are found in South America and South Asia, but they are not yet found in the United States. Wheat blast caused by the MoT fungus was first reported in Brazil in 1985 and subsequently spread to Bolivia, Paraguay and Argentina in the 1990s and 2000s. The disease first appeared in Bangladesh in 2016 and in Zambia in 2017. The MoT fungus is seed borne, and the most likely route for movement across oceans was though grain trade. Wheat head (spike) blast is the predominant form of the disease in the field, although foliar and stem blast also occurs. The disease has proven hard to control when weather conditions are conducive, often resulting in devastating yield and quality losses. The only currently effective resistance, contained in the 2NvS translocation from the wild wheat relative Aegilops ventricosa, confers partial resistance that is variable depending on the genetic background of the specific wheat variety. Fungicides are not fully effective in controlling wheat head blast if warm, humid weather occurs during the heading stage. A major disease management strategy in areas where the disease occurs involves timing the wheat planting date so that heading does not coincide with warm rainy weather. A ‘wheat holiday’ strategy of not growing wheat at all for a few years has been implemented in South Asia to attempt to block further spread of the pathogen. However, MoT is clearly established in wheat, and now also in triticale, in Bangladesh. A climate suitability model for the U.S., based on weather patterns from 1997 to 2006, indicates that all of U.S. soft red winter wheat (SRWW) and about half of the hard red winter wheat (HRWW) are at risk for wheat blast establishment. Molecular diagnostics are needed to differentiate potential exotic MoT strains from the closely-related U.S. Lolium pathotype (MoL) strains, infecting Lolium turf and forage grasses as primary hosts. Some native MoL strains can infect wheat as a secondary host in controlled environment assays, although they are not as aggressive towards wheat as MoT strains. An effective wheat blast diagnostic protocol has been developed and will be deployed through the National Plant Diagnostics Network to differentiate exotic MoT strains from native MoL strains. Availability of MoT diagnostics has enabled incorporation of official wheat blast surveys in the APHIS National Cooperative Agricultural Pest Survey (CAPS) Program, beginning in 2021. Challenges to detection of wheat blast invasion in a timely manner include the superficial resemblance of bleached heads from wheat blast to symptoms of Fusarium head blight, which is widely established in the U.S. and occurs under similar environmental conditions. Extension materials and identification aids are essential to train individuals doing surveys to differentiate wheat blast from Fusarium head blight. Imagery is useful for decision-making in agriculture. Syndromic data can provide adequate information from plant populations and be directly applicable to the surveillance and response to wheat blast. Developing and deploying a U.S. wheat blast forecasting model is essential to focus surveys to locations and times with environmental conditions that favor blast disease. Wheat blast is a moving target because the fungus is still evolving and becoming a better wheat pathogen. Recently-isolated MoT strains are more aggressive than previously-isolated strains in causing disease on wheat and some recent MoT strains appear to have overcome 2NvS-mediated resistance. Although wheat blast is mainly known as a head (spike) disease in the field, leaf blast is increasingly reported, and new epidemiological data supports l