Bridging Classical and Molecular Genetics of Sorghum Disease Resistance
With rare exceptions, sorghum breeders have been highly successful in producing disease-resistant sorghums. Classical breeding techniques, including identification of resistant cultivars from large and readily available germplasm collections, crosses to e
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Bridging Classical and Molecular Genetics of Sorghum Disease Resistance Clint W. Magill
Abstract With rare exceptions, sorghum breeders have been highly successful in producing disease-resistant sorghums. Classical breeding techniques, including identification of resistant cultivars from large and readily available germplasm collections, crosses to elite but susceptible varieties, followed by backcrosses, selfing, and selection, have been used to develop disease-resistant breeding and commercial lines. However, for almost every disease, the breeding efforts must be continuous as new forms of the pathogens rapidly evolve to overcome resistance. Molecular tools that allow rapid and accurate tagging and identification of resistance genes permit, at the very least, the ability to use marker-assisted selection to combine different genes and to test the theory that stacking different genes for resistance will provide stable resistance. Knowledge of the nature and molecular functions of resistance genes promises much more: the ability to manipulate, alter, and enhance the signal transduction pathways that actually trigger host plant resistance. Keywords Genetic resistance • Sorghum pathogens • Disease screening • Germplasm • Germplasm screening • Cytoplasmic male sterility • NBS-LRR resistance genes • Host defense responses • Durable resistance • Gene stacking • Quantitative trait loci
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Background
As is true with all crop species, sorghum has its share of pathogens that can limit grain or forage production. While both bacterial and viral diseases occur wherever sorghum is grown, fungi cause most of the diseases that are reported. As will be
C.W. Magill (*) Department of Plant Pathology and Microbiology, Texas A&M University, Room 202H LF Peterson Building 2132 TAMU, College Station, TX 77843-2132, USA e-mail: [email protected] A.H. Paterson (ed.), Genomics of the Saccharinae, Plant Genetics and Genomics: Crops and Models 11, DOI 10.1007/978-1-4419-5947-8_15, © Springer Science+Business Media New York 2013
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described, an oömycete and a parasitic weed are also pathogens of sorghum, whereas there are conflicting reports concerning nematodes. The manual “Descriptors for Sorghum” published jointly by the International Board for Plant Genetics Resources and the International Crops Research Institute for the Semi Arid Tropics requests all donors of accessions to the sorghum germplasm collection to provide information, when available, on susceptibility to 21 insects, 19 fungi, 3 bacteria, 5 viruses, and 3 Striga (parasitic weed) species. Although many nematode species have been reported to reproduce sufficiently on sorghum to reduce yields (Kollo 2002), the request does not mention nematodes. However, nematodes are included in the most recent Compendium of Sorghum Diseases (Frederiksen and Odvody 2000), a compilation that also includes description of 6 bacterial diseases, 8 viruses, approximately 29 fungal diseases, and 7 virus or MLO diseases. Examples of resistance breeding for each category of pat
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