Perennial Wheat Germ Plasm Lines Resistant to Eyespot, Cephalosporium Stripe, and Wheat Streak Mosaic

The Palouse Prairie of eastern Washington was identified in the 1997 USDA National Resources Inventory as one of the most highly erodible areas in the United States. It is estimated that 10% of the original topsoil in eastern Washington has been lost since cultivation began in the region in the late 1800s (32). Furthermore, runoff from agricultural land reduces water quality in streams and rivers (34), and dust is the leading air pollutant in Washington (33). Healthy stands of perennial grasses like those established under the Federal Conservation Reserve Program (CRP) reduce soil erosion (17) and competition from weeds (8), restore soil nutrients (9), increase soil quality (11), and increase wildlife habitat (24). Over 29 million acres of highly erodible agricultural land in the United States are currently enrolled in CRP with over 2 million acres located in Washington, Oregon, and Idaho. However, there are more acres of land considered highly erodible than can be enrolled in the current program. Thus, alternative solutions for soil erosion control are needed that are ecologically and economically sustainable. Perennial wheat has the potential to convert unprofitable land back into production, save state and federal money, conserve agricultural land and natural resources, and provide a profitable crop for growers. Past efforts to develop perennial wheat for grain production were begun in the 1920s (30,31). Sando hybridized domestic wheat with wheatgrass (then called Agropyron spp.) and selected for perennial habit (36), as did Suneson (28) and Suneson and Pope (29). The best perennial lines of those programs yielded only 60% of the grain of the best annual varieties and the project was abandoned because yield was the ultimate goal (29). The loss of topsoil that results in nonpoint source water pollution and reduces soil productivity over time has resulted in a renewed interest in perennial wheat. Cultural practices such as modification of seeding date and tillage that are used to reduce disease in conventional and no-till wheat production systems are of limited value in a perennial wheat crop. Inoculum of many pathogens is capable of surviving from crop to crop in senescent tissue, in live root and crown tissue, and in perennial plants (4). Perennial wheat must contain appropriate disease resistance genes for locally important diseases for it to be feasible. Furthermore, resistance must be durable and suppress disease below an economic threshold to reduce external inputs and enhance the profitability of perennial wheat (37). It is possible that combining genotypes and pyramiding resistance genes from wild relatives of wheat that durable resistance can be achieved within a perennial wheat cropping system. Perennial wheat is essentially a notillage system with persistent crowns and residue in the soil and as such, could potentially serve as a reservoir for pathogens that survive in plant debris (4). Eyespot, Cephalosporium stripe, and wheat streak mosaic (WSM) caused by Tapesia yallundae Wallwork & Spooner and T. acuformis (Boerma, Pieters & Hamers) Crous (anamorphs Pseudocercosporella herpotrichoides (Fron.) Deighton var. herpotrichoides and var. acuformis, respectively), Cephalosporium gramineum Nisikado & Ikata, and Wheat streak mosaic virus (WSMV), respectively, are among the most significant diseases in the intermediateand low-rainfall regions of Washington for which perennial wheat is being developed (12). The fungi that cause eyespot and Cephalosporium stripe survive in crop residues (38) and thus, may be favored in a perennial wheat cropping system. Likewise, annual wheat escapes infection by WSMV in most years because it dies and does not overlap with potential reservoir hosts. Perennial wheat, by virtue of its regrowth after harvest, may become infected by WSMV resulting in less productivity, shorter stand duration, and it may serve as an inoculum reservoir for nearby annual small grain crops. Several wheatgrasses are resistant to many of the diseases that infect annual wheat, which include Cephalosporium stripe, WSM, stripe rust, leaf rust, and barley yellow dwarf (6,7,13,15). Despite efforts by breeders to exploit the genetic resources of the wheatgrasses and other members of the Triticeae, winter wheat cultivars adapted for production in the Pacific Northwest with highly effective resistance to Cephalosporium stripe and/or WSM are not available (13). Control of these diseases has relied on cultural practices such as elimination of volunteer wheat to prevent carryover of virus and vectors from spring to winter crops, 3-year rotations between susceptible wheat crops, destruction of residue by tillage or burning, and delayed seeding in the autumn (23,38). Eyespot is controlled largely with diseaseresistant cultivars and foliar fungicides (10,22,23). Cultural practices such as seeding date and tillage for disease control will not be feasible in a perennial wheat cropABSTRACT Cox, C. M., Murray, T. D., and Jones S. S. 2002. Perennial wheat germ plasm lines resistant to eyespot, Cephalosporium stripe, and wheat streak mosaic. Plant Dis. 86:1043-1048.