WERA_OLD97: DISEASES OF CEREALS
(Multistate Research Coordinating Committee and Information Exchange Group)
Status: Inactive/Terminating
WERA_OLD97: DISEASES OF CEREALS
Duration: 10/01/2010 to 09/30/2015
Administrative Advisor(s):
NIFA Reps:
Non-Technical Summary
Statement of Issues and Justification
The cereal grains, particularly wheat and barley, constitute major cash crops throughout the western region of the United States. The types of cereal grains produced are diverse, including soft white winter, soft white spring, club, hard red winter, hard red spring, and durum wheat classes; 2-row and 6-row winter and spring feed and malting barley types; hay, grain and/or forage oat types; and grain and/or forage triticale types. Areas of production for these diverse crops overlap throughout the western region, and production occurs in both high and low rainfall areas, with or without irrigation, and under a wide-range of other production inputs (level of fertilization and degree of weed, insect, and disease control inputs). Overall, western cereal production is geared for the bulk commodity and specialized niche domestic markets as well as for export. In these markets, profit margins are slim and to remain competitive, cereal producers desperately seek assistance to reduce operating costs and minimize disease losses.
To maintain profitability in a diverse and changing disease environment requires constant surveillance and rapid responses to emergent disease problems. Over the last five years, several important cereal diseases have emerged in the Western United States. The most notorious of these have been Fusarium head blight and stripe rust of wheat and barley. In 2004, Fusarium head blight (scab) spread from the corn-belt states and Northern Great Plains into Inter-mountain regions of the Western U.S. causing millions of dollars in lost production. While losses are not as pervasive as in the Great Plains, individual growers experience catastrophic losses that can only be addressed through adapting head blight control measures to local situations. This includes development of resistant cultivars suited to local production systems, the validation of previously developed disease models, and utilization of specific agronomic practices and fungicides to reduce infection and toxin accumulation. In this situation, professional connections established through WERA-97 helped provide technical support that enhanced research responses. In contrast to Fusarium head blight, new races of stripe and leaf rust annually migrate eastward from Pacific coastal areas and northward from the Gulf states into central and northwestern regions. With ever changing virulence profiles, maintaining effective varietal resistance to both stripe rust and leaf rust requires constant vigilance. When resistance breaks down, the consequences are dramatic as seen with the 2003 stripe rust epidemic which caused an estimated 89 million bushels in lost wheat production. By enhancing cross communication among USDA rust specialists, state plant pathologists and breeders, more coordinated and responsive breeding efforts are being conducted than would otherwise be possible.
In addition to emerging diseases, changes in production practices to more intense, no-till cereal production has lead to shifts in disease dynamics. Increases in severity and incidence of Cephalosporium stripe, Fusarium crown rot, common root rot, root lesion nematodes, eyespot, and wheat streak mosaic have been documented. These diseases are persistent, endemic threats that have increased in severity and incidence in the past decade. Maintaining WERA-97 is instrumental in addressing these issues on regional and national basis. Looking to the future, WERA-97 is providing a forum to address emerging threats. In particular, new races of stem rust found in North Africa are currently spreading across central Asia and can be expected to reach North America in the coming decade. In these environments of constantly changing disease dynamics, the relationships developed through WERA-97 between USDA scientists, university and local researchers are vital to maintaining a safe and secure U.S. cereal production system.
With states having limited resources to address the plethora of disease related losses, responses need to be efficiently obtained through coordinated efforts of state and regional programs. By providing a forum for communication and collaboration, WERA-97 enhances synergy amongst participating members, minimizes redundancy and ultimately provides a more responsive targeting of research and extension efforts to assist producers in reducing disease related losses. Current member states include California, Colorado, Idaho, Kansas, Minnesota, Montana, Nebraska, North Dakota, Oregon, South Dakota, Texas, Utah, and Washington. The Committee welcomes participation and input from states outside the region and is reaching out to currently non-participating western states to solicit their involvement. Joint meetings with NCERA-184 at Idaho Falls, Idaho, in 2007, the Western Wheat Workers and the NCERA-184 at Davis, California, in 2008, and with the Western Wheat Workers at Corvallis, Oregon, in 2009 are good examples of the Committee reaching out to a wider spectrum of researchers and disciplines related to plant pathology.
Objectives
-
" Provide a forum for the communication and coordination of cooperative efforts in cereal pathology research, extension and education in the western United States through an annual meeting.
-
" Enhance cooperative research among committee members and their respective states, thereby achieving maximum efficiency, through the exchange of biological materials and methodologies, communication via the internet, and the publication of appropriate research and extension materials.
-
" Coordinate Extension programs for cereal disease control that will carry research results to growers via publications, commodity schools, and the internet. This will be especially important to cereal producers in the region dealing with emerging and reemerging diseases including wheat stripe rust, leaf rust, winter injury, root lesion nematodes, Fusarium head blight (scab), net blotch, tan spot, wheat streak mosaic and others.
Procedures and Activities
As demonstrated by past successes, WERA-97 acts as source of research coordination, communication, education and professional development. As a blanket organization, WERA-97 positions researchers, extension personnel, and growers to respond more effectively and rapidly to emerging disease problems through early identification of new diseases, constant monitoring of existing diseases, increased intra-regional cooperation and more rapid exchange of information on techniques and control strategies. Use of the internet and e-mail allows researchers to communicate early detection of diseases as they develop. WERA-97 has a proven record of performance in addressing dynamic disease systems in United States. In the past:
WERA-97 acted as a forum for coordination of research activities within the western region on both wheat stripe rust (WSR) and barley stripe rust (BSR). Members of the Committee were involved in the initial detection of BSR and later developed methods for monitoring its progress. Now that stripe rust is firmly established in the region, efforts on breeding for resistance are proving fruitful and continued screening for new sources of resistance is being coordinated by several members of the Committee. Expanded efforts on WSR following the epidemics of 2000-2004 and the rapid development and establishment of new races has stimulated increased efforts at integrating control of WSR, the development of a National Research Initiative for WSR, and an expanded screening program to identify new sources of both seedling and adult plant resistance for the Western Region.
WERA-97 educated its own members and other invited academic and industry participants in joint meetings with various groups, such as the Western Wheat Workers, NCERA-184, and WestBred LLC. Participants learned about the epidemiology, impact and management of numerous diseases including Fusarium head blight, wheat streak mosaic, Fusarium crown rot, wheat stripe rust, and root lesion nematode. Much of this information is of tremendous immediate importance to growers. For instance, participants learned about the toxin dynamics related to Fusarium head blight, effective fungicides to reduce both disease and vomitoxin (deoxynivalenol) accumulation, and how inoculum loads and harvest timing affect levels of toxin present in the grain.
WERA-97 keeps participants informed on changes in resources and available personnel to address disease issues, and enhances understanding and communication between private and public sector services. This information enables more efficient resource allocation and ensures critical issues continue to be addressed.
To enhance communication and coordination, WERA-97 established a website (http://plantsciences.montana.edu/wera97/Default.htm) and an electronic bulletin board (wcc97@listserv.montana.edu). These serve committee members and our clientele by providing useful information in a timely manner and permit rapid dissemination of information. In addition, WERA-97 has been actively involved in facilitating the publication of materials regarding cereal diseases for use by farmers, extension personnel, and researchers. Its members played a major role in the production of the 2nd edition of the Compendium of Barley Diseases and the just published 3rd edition of the Compendium of Wheat Diseases and Pests (currently on sale and due out in April/May 2010).
WERA-97 provided a forum for USDA-scientists to keep state pathologists abreast of rust dynamics. Participants were alerted to the vulnerability of North American wheat to the newest stem rust race from work conducted by Dr. Yue Jin of the USDA Cereal Disease Laboratory, St Paul, MN. Additional annual updates for leaf and stripe rusts are publicly available for wheat and barley breeders to incorporate appropriate disease resistance genes for their respective regions.
Expected Outcomes and Impacts
- The Committee provides a forum for the communication and coordination of cooperative efforts in cereal pathology research, extension and education in the western United States, specifically through interactions at annual meetings, the exchange of biological materials and methodologies, the use of an electronic bulletin board, and the publication of appropriate research and extension materials.
- Improved communication among committee members and their respective states, thereby achieving maximum efficiency of research efforts.
- Extension programs for cereal disease control will thus more rapidly carry research results to growers via publications and commodity schools and Agalerts . This will be especially important as cereal producers in the region deal with a myriad of emerging and reemerging diseases including barley stripe rust, wheat stripe rust, stem rust, root lesion nematodes, Fusarium head blight (scab), net blotch, tan spot, wheat streak mosaic.
Projected Participation
View Appendix E: ParticipationEducational Plan
Research, extension, and teaching members involved with the committee will communicate with and invite participation by plant pathology from the USDA and private industry. Currently, at least one-third of our members have extension appointments. Through them, information will be provided to growers on emerging and/or new disease problems in their areas. Members of the Committee played a major role in the production of the new addition of the Compendium of Wheat Diseases currently available through the American Phytopathological Society.
Organization/Governance
The Chairman is elected at the annual meeting and serves the following year. This person serves as a liaison with the Administrative Advisor to see that all required annual reports are submitted to the office of the Executive Director, Western Association of Agricultural Experiment Station Directors. The Chairman directs the activities of the Committee and makes sure that the objectives of the committee are fulfilled. The following years meeting of the committee usually is at the home base of the Chairmen, who then also serves as local arrangements chair. Minutes of the meeting, state reports, and information about the activities of WERA-97 are posted on the Committees website(http:plantsciences.montana.edu/wera97/Default.htm). Meetings normally alternate among the Great Plains and western states, although alternate sites are sometimes selected to expand committee perspectives and impacts. For examples, the 2005 site was in Lethbridge, Alberta and the 2006 meeting was held jointly with NCERA-184, our sister committee, in Fargo, North Dakota.
Literature Cited
Al-Naimi, F. A., Garrett, K. A., and Bockus, W. W. 2005. Competition, facilitation, and niche differentiation in two foliar pathogens. Oecologia 143:449-457.
Allen, T., H. Maples, F. Workneh, J. Stein, and Rush, C. 2008. Distribution and recovery of Tilletia indica teliospores from regulated wheat fields in Texas. Plant Dis. 92:344-350.
Babcock, C., Chen, X. M., Crous, P. W., Dugan, F. M., Goates, B. and Green, P. N. 2007. Plant germplasm centers and microbial culture collections: A users guide to key genetic resources for plant pathology. Plant Dis. 91:476-484.
Baenziger, P. S., Beecher, B., Graybosch, R. A., Ibrahim, A. M. H., Baltensperger, D. D., Nelson, L. A., Jin, Y., Wegulo, S. N., Watkins, J. E., Hatchett, J. H., Chen, M-S., and Bai, G. 2008. Registration of NE01643 wheat. J. Plant Reg. 2:36-42.
Bockus, W. W., Su, Z., Garrett, K., A., Gill, B. S., Stack, J. P., Fritz, A. K., Roozeboom, K. L., and Martin, T. J. 2007. Number of experiments needed to determine wheat disease phenotypes for four wheat diseases. Plant Dis. 91:103-108.
Burlakoti, R. R., Ali, S., Secor G. A., Neate, S. M., McMullen, M. P., and Adhikari, T. B. 2008. Genetic relationships among populations of Gibberella zeae from barley, wheat, potato, and sugar beet in the Upper Midwest of the United States. Phytopathology 98:969-976.
Burlakoti, R.R., Ali, S., Secor, G.A., Neate, S.M., McMullen, M.P., and Adhikari, T.B. 2008. Comparative mycotoxin profiles of Gibberella zeae populations from barley, wheat, potato, and sugar beet. Applied and Environmental Microbiology (AEM) 74:6513-6520.
Chen, X. M., and Wood, D. A. 2008. Control of stripe rust of winter wheat with foliar fungicides, 2007. Plant Disease Management Report 2:CF015.
Chen, X. M. 2007. Challenges and solutions for stripe rust control in the United States. Aust. J. Agric. Res. 58:648-655.
Coram, T. E., Settles, M. L., and Chen, X. M. 2008. Transcriptome analysis of high-temperature adult-plant resistance conditioned by Yr39 during the wheat-Puccinia striiformis f. sp. tritici interaction. Mol. Plant Pathol. 9:479-493.
Coram, T. E., Settles, M. L., Wang, M. N., and Chen, X. M. 2008. Surveying expression level polymorphism and single-feature polymorphism in near-isogenic wheat lines differing for the Yr5 stripe rust resistance locus. Theor. Appl. Genet. 117:401-411.
Coram, T. E., Brown-Guedira, G., and Chen, X. M. 2008. Using transcriptomics to understand the wheat genome. CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources 3. No.083.
Coram, T., Wang, M. N., and Chen, X. M. 2008. Transcriptome analysis of the wheat-Puccinia striiformis f. sp. tritici interaction. Mol. Plant Pathol. 9(2):157-169.
Cowger, C., Brunner, P.C., and Mundt, C.C. 2008. Frequency of sexual recombination by Mycosphaerella graminicola in mild and severe epidemics . Phytopathology 98:555-561.
Cox, C. M., Garrett, K. A., Cox, T. S., Bockus, W. W., and Peters, T. 2005. Reactions of perennial grain accessions to four major cereal pathogens of the Great Plains. Plant Dis. 89:1235-1240.
Cox, C. M., Garrett, K. A., and Bockus, W. W. 2005. Meeting the challenge of disease management in perennial grain cropping systems. Renewable Agric. and Food Sys. 20:15-24.
Culler M.D., Miller-Garvin J.E., and Dill-Macky R. 2007. Effect of extended irrigation and host resistance on deoxynivalenol accumulation in Fusarium-infected wheat. Plant Disease 91:1464-1472
Dyer, A.T., Johnston, R.H., Hogg, A.C., and Johnston, J.A. 2009. Comparison of pathogenicity of the Fusarium crown rot complex (F. culmorum, F. pseudograminearum and F. graminearum) on hard red spring and durum wheat. Eur. J. Plant Pathol. DOI: 10.1007/s10658-009-9488-1.
Franzen, D.W., McMullen, M.V., and Mosset, D.S. 2008. Spring wheat and durum yield and disease responses to copper fertilization of mineral soils. Agronomy J. 100:371-375.
Guttieri M.J., O'Brien K., Becker C., Stark J.C., Windes J., Souza E. 2006. Managing nitrogen fertility of irrigated soft white spring wheats for optimum quality. Canadian Journal of Plant Science 86: 459-464.
Gautam, P., Dill-Macky, R. 2009. Pre-harvest moisture impacts wheat quality through Fusarium head blight (FHB) development and deoxynivalenol (DON) accumulation
Phytopathology 99: S159-S159
Hogg, A.C., Johnston, R.H., Kephart, K.D., Klouser, L. and Dyer, A.T. 2010. Monitoring Fusarium populations in wheat residues using quantitative real-time PCR. Phytopathology 100:49-57
Hogg, A.C., Johnston, R.H., and Dyer, A.T. 2007. Applying quantitative real time PCR to Fusarium crown rot of wheat. Plant Dis. 91:1021-1028
Kabage, M., Leslie, J. F., Hulbert, S. H., and Bockus, W. W. 2009. Comparison of natural populations of Mycosphaerella graminicola from single fields in Kansas and California. Physiological and Molecular Plant Pathology. doi:10.1016/j.pmpp.2009.002 (KAES #07-205
Kabbage, M., Leslie, J. F., Zeller, K. A., Hulbert, S. H., and Bockus, W. W. 2008. Genetic diversity of Mycosphaerella graminicola, the causal agent of Septoria tritici blotch, in Kansas winter wheat. J. Agric. Food Environ. Sci. vol. 2 (online) http://www.scientificjournals.org/journals2008/articles/1377.pdf
Krenz, J.E, Sackett, K.E., and Mundt, C.C. 2008 Specificity of incomplete resistance to Mycosphaerella graminicola in wheat . Phytopathology 98:555-561.
Lin, F., and Chen, X. M. 2008. Molecular mapping of genes for race-specific overall resistance to stripe rust in wheat cultivar Express. Theor. Appl. Genet. 116:797-806.
Lin, F., and Chen, X. M. 2007. Genetics and molecular mapping of genes for race-specific all-stage resistance and non-race specific high-temperature adult-plant resistance to stripe rust in spring wheat cultivar Alpowa. Theor. Appl. Genet.114:1277-1287.
Ling, P., Wang, M. N., Chen, X. M., and Campbell, K. G. 2007. Construction and characterization of a full-length cDNA library for the wheat stripe rust pathogen (Puccinia striiformis f. sp. tritici). BMC Genomics 8:145.
Li, Y., Niu, Y. C., and Chen, X. M. 2009. Mapping a stripe rust resistance gene YrC591 in wheat variety C591 with SSR and AFLP markers. Theor. Appl. Genet. 118:339-346.
Li, H. J., R. L. Conner, and Murray, T.D. 2008. Resistance to soil-borne diseases of wheat: Contributions from the wheatgrasses Thinopyrum intermedium and Th. ponticum. Can. J. Plant Sci. 88:195-205.
Li, H. J., M. Arterburn, S.S. Jones, and Murray, T.D. 2005. Resistance to eyespot of wheat, caused by Tapesia yallundae, derived from Thinopyrum intermedium homoeologous group 4 chromosomes. Theoretical and Applied Genetics 111:932-940 (DOI: 10.1007/s00122-005-0025-0).
McCallum, B. D., Chen, X. M., Shorter, S., Sadasivaiah, R. S., and Tewari, J. P. 2007. Stripe rust reaction of twenty eight Canadian wheat cultivars. Can. J. Plant Pathol. 29:401-407.
MacDonald, J., C. Allen, D. Gadoury, W. Jacobi, S. Kelemu, J. Moyer, T. Murray, K. Ong, C. Pearson, J. Sherwood, and A. Vidaver. 2009. Education in plant pathology: Present status and future challenges. Plant Disease 93:1238-1251.
McMullen, M., Markell, S., Knodel, J. 2008. 2008 North Dakota IPM Field Crop Disease Survey. Pages 14-18 in: NDSU 2009 Crop Production Guide No. 19, NDSU Extension Service. 271 p.
McMullen, M., Markell, S., and Rasmussen, J. 2008. Rust diseases of wheat in North Dakota. NDSU Extension Circular PP-1361. 4 p.
Mundt, C. C., Sackett, K. E., Wallace, L. D., Cowger, C., and Dudley, J. P. 2009. Long distance dispersal and accelerating waves of disease: Empirical relationships. American Naturalist 173:456-466.
Mundt, C.C., Brunet, J., and Sackett, K.E. 2008. Impact of density and disease on frequency-dependent selection and genetic polymorphism: Experiments with stripe rust and wheat. Evolutionary Ecology 22:637-657.
Murray, T.D., H. Pappu, and Smiley R.W. 2009. First report of Soilborne wheat mosaic virus in Washington State. Plant Health Progress doi:10.1094/PHP-2009-1204-01-BR.
Murray, T.D. 2006. Seed infection and transmission of Cephalosporium gramineum in commercial winter wheat varieties. Plant Disease 90:803-806.
Nirmala, J., Dahl, S., Steffenson, B., Kannangara, C. G., von Wettstein, D., Chen, X. M., and Kleinhofs, A. 2007. Proteolysis of the barley receptor-like protein kinase Rpg1 by a proteasome pathway is required for Rpg1 mediated stem rust resistance. PNAS 104:10276-10281.
Nishio, Z., N. Iriki, K. Takata, M. Ito, T. Tabiki, and Murray, T.D. 2008. Influence of Cold-hardening and Soil Matric Potential on Resistance to Speckled Snow Mold in Wheat. Plant Disease 92:1021-1025.
Osborne, L.E., and J.M. Stein. 2007. Epidemiology of Fusarium Head Blight on Small Grain Cereals. Intl. J. Food. Microbiol. 119:103-108.
Paul, P., P. Lipps, G. Shaner, G. Buechley, T. Adhikari, S. Ali, J. Stein, L. Osborne, and L. Madden. 2007. A distributed-lag analysis of the relationship between Gibberella zeae inoculum density on wheat spikes and weather. Phytopath. 97:1608-1624.
Perez, C., Dill-Macky R., Kinkel L.L. 2008. Management of soil microbial communities to enhance populations of Fusarium graminearum-antagonists in soil. Plant and Soil 302:53-69.
Ransom, J.K., and McMullen, M.V. 2008. Yield and disease control on hard winter wheat cultivars with foliar fungicides. Agronomy J. 100:1130-1137.
Richardson , K.L., Vales, M.I. Kling, JG., Mundt, C.C., and Hayes, P.M. 2006. Pyramiding and dissecting disease resistance QTL to barley stripe rust. Theoretical and Applied Genetics 113: 485-495.
Rossi, C., Cuesta-Marcos, A., Vales, I., Gomez-Pando, L., Orjeda, G., Wise, R., Sato, K., Hori, K., Capettini, F., Vivar, H., Chen, X. M., and Hayes, P. 2006. Mapping multiple disease resistance genes using a barley mapping population evaluated in Peru, Mexico, and the USA. Molecular Breeding 18:355-366.
Rush, C.M., J.M. Stein, R.L. Bowden, R. Riemenschneider, T. Boratynski, and M.H. Royer. 2005. Status of Karnal Bunt of wheat in the United States: 1996 to 2004. Plant Dis. 89:212-223.
Sackett, K. E., and Mundt, C. C. 2009. Effect of plot geometry on epidemic velocity of wheat yellow rust. Plant Pathology 58:370-377.
Santra, D. K., Chen, X. M., Santra, M., Campbell, K. G., and Kidwell, K. K. 2008. Identification and mapping QTL for high-temperature adult-plant resistance to stripe rust in winter wheat (Triticum aestivum L.) cultivar Stephens. Theor. Appl. Genet. 117:793-802.
Singh, S., Bockus, W. W., Sharma, I, and Bowden, R. L. 2008. A novel source of resistance in wheat to Pyrenophora tritici-repentis race 1. Plant Dis. 92:91-95.
Smith, K. M. Draper, K. Simmons, R. Bennett, P. Hebbar, M. Royer, and Murray, T. 2009. Management strategies for new wheat stem rust strains in the U.S. Outlooks on Pest Management 20:148-52.
Stein, J.M., H.W. Maples, and Rush, C.M. 2005. Epidemiology of Tilletia indica teliospores in regulated wheat fields in Texas. Plant Dis. 89:828-833.
Uauy, C., Brevis, J. C., Chen, X. M., Khan, I. A., Jackson, L. F., Chicaiza, O., Distelfeld, A., Fahima, T, and Dubcovsky, J. 2005. High-temperature adult plant (HTAP) stripe rust resistance gene Yr36 from Triticum turgidum ssp. dicoccoides is closely linked to the grain protein content locus Gpc-B1. Theor. Appl. Genet. 112:97-105.
Vales, M. I., Schön, C. C., Capettini, F., Chen, X. M., Corey, A. E., Mather, D. E., Mundt, C. C., Richardson, K. L., Sandoval-Islas, J. S., Utz, H. F., and Hayes, P. M. 2005. Effect of population size on the estimation of barley stripe rust QTL. Theor. Appl. Genet. 111:1260-1270.
Wan A. M., Chen, X. M., and He, Z. H. 2007. Wheat stripe rust in China. Australian Journal of Agricultural Research. 58:605-619.
Wegulo, S. N., and Dowell, F. E. 2008. Near-infrared versus visual sorting of Fusarium-damaged kernels in winter wheat. Can. J. Plant Sci. 88:1087-1089.
Windes J, Shelman T, Jackson CA. 2009. Resistance to crown and foot rot in wheat cultivars grown in Idaho. Phytopathology 99: S142-S142.
Worster, C.A. , and Mundt, C.C. 2007. The effect of diversity and spatial arrangement on biomass of agricultural cultivars and native plant species. Basic and Applied Ecololgy 8:521-532.
Yan, G. P., and Chen, X. M. 2008. Identification of a quantitative trait locus for high-temperature adult-plant resistance against Puccinia striiformis f. sp. hordei in Bancroft barley. Phytopathology 98:120-127.
Yan, G. P., and Chen, X. M. 2007. Molecular mapping of the rps1.a recessive gene for resistance to stripe rust in BBA 2890 barley. Phytopathology 97:668-673.
Yan, G. P., and Chen, X. M. 2006. Molecular mapping of a recessive barley gene for resistance to stripe rust. Theor. Appl. Genet. 113:529-537.
Zhang, L., Lavery, L., Gill, U., Gill, K., Steffenson, B. Yan, G. P., Chen, X. M., and Kleinhofs, A. 2008. A cation/proton-exchanging protein is a candidate for the barley NecS1 gene controlling necrosis and enhanced defense response to stem rust. Theor. Appl. Genet. 118:385-397.
Zhan, J., Mundt , CC, and McDonald, B.A. 2007. Sexual reproduction facilitates the adaptation of parasites to antagonistic host environments: evidence from a field experiment in the wheat -Mycosphaerella graminicola system. International Journal of Parasitology 37:861-870.