Reactions of Perennial Grain Accessions to Four Major Cereal Pathogens of the Great Plains

Problems associated with annual grain agriculture, such as soil erosion and water and air pollution, indicate that reliance on annual grain production is a fundamental problem of current agricultural practice (23). Annual plant roots are less efficient micromanagers of water, soil, and soil nutrients than their perennial counterparts, resulting in nutrient and pesticide contamination of water sources even when best management practices are employed (12,22,32,35,36). Successful production of perennial, herbaceous grains could profoundly reduce these adverse effects of agriculture (10,11,29,33). Methods of disease management used in annual grain crops, especially cultural practices designed to disrupt the disease cycle of a particular pathogen, such as short rotations, tillage, and delayed fall planting, will not necessarily be applicable to perennial grain crops. Practices such as deployment of crops in mixtures, intercrops, or polycultures may be an important component in perennial grain agriculture (4,7,8,17,18,30,46). But whether perennials are mixed within polycultures or uniform in monocultures, resistance to a set of locally important cereal diseases will be an essential managerial component (3,7). Wheatgrasses (Thinopyrum spp.), the perennial donors in perennial wheat breeding programs, are resistant to many of the diseases that infect annual wheat, including wheat streak mosaic (WSM), stripe rust, leaf rust, and barley yellow dwarf (BYD) (14,15,24,26). In greenhouse experiments, several perennial wheat germ plasm lines (Thinopyrum spp. × Triticum aestivum hybrids) demonstrated high levels of resistance to Cephalosporium stripe (caused by Cephalosporium gramineum Nisikado & Ikata), eyespot (caused by Tapesia yallundae Wallwork & Spooner and T. acuformis (Boerma, Pieters & Hamers) Crous (anamorph Pseudocercosporella herpotrichoides (Fron.) Deighton var. herpotrichoides and var. acuformis, respectively)), and WSM, three important wheat diseases of the Pacific Northwest region of the United States where perennial wheat is also being considered (9,40). Tan spot and take-all are important residueand soilborne diseases of wheat, caused by Pyrenophora tritici-repentis (Died.) Drechs. and Gaeumannomyces graminis (Sacc.) Arx & D. Olivier var. tritici J. Walker, respectively. P. tritici-repentis causes leaf lesions initiated by windand splashed-dispersed ascospores, or winddispersed conidia, while G. graminis var. tritici infects roots and crowns and can kill entire plants (45). Perennial crowns and persistent residue in the soil could potentially serve as a reservoir for these pathogens as well as for other pathogens that share similar life histories. By virtue of regrowth after harvest, perennial plants emerge and assimilate carbon well before adjacent, newly sown annual relatives (11). This provides more opportunities for infection by viruses that rely on the “green bridge” of susceptible hosts, such as Barley yellow dwarf virus (BYDV) and Wheat streak mosaic virus (WSMV) (45). Combined resistance to WSM and BYD, therefore, as well as to tan spot and take-all, is desirable for longevity and successful production of perennial grains in this region. The objective of this research was to evaluate disease resistance in 10 perennial grain accessions to tan spot, take-all, wheat streak mosaic, and barley yellow dwarf, four important diseases of the central Great Plains of the United States.