|Barley crown rust|
Crown rust is a new disease of barley. It was found first in a barley breeding nursery near Clay Center, Nebraska in 1992. Since then, crown rust has been found throughout the upper Midwest, with greatest incidence in the central Red River Valley of North Dakota and Minnesota. In that region the alternate host, common buckthorn (Rhamnus cathartica), grows abundantly in shelter belts and riparian areas. Since 1993, outbreaks of crown rust have occurred on barley and forage grasses at several localities in this region. The extent of yield losses in barley caused by this disease have not been determined. Crown rust poses a threat to barley production, because the first infections in barley occur early in the season from local inoculum.
Uredinia are linear, light orange, and occur mostly on the leaf blades but occasionally occur also on leaf sheaths, peduncles and awns. Extensive chlorosis is often associated with the uredinia. Telia are mostly linear, black to dark brown, and are covered by the host epidermis.
Crown rust of barley is caused by a variant of Puccinia coronata Corda. The uredinial and telial stages are morphologically distinct from common crown rust forms found on oat, Lolium spp. or Festuca spp. Its taxonomic position is currently being investigated.
Disease Cycle and Control:
Teliospores on barley straw and residue of susceptible grasses left in the field germinate in the spring and produce basidiospores that infect R. cathartica. Pycnial and aecial stages are produced on the alternate host. Aeciospores from R. cathartica are the primary inoculum for infecting barley. The primary infections, which can occur as early as the three leaf stage of barley in the spring, develop into uredinia. Urediniospores produced in the uredinia repeat the infection process, and the fungus undergoes several cycles of reproduction on barley during the growing season. Spread by wind-borne urediniospores can carry the fungus some distance from the R. cathartica bushes that were the original sources of primary inoculum, although such secondary spread seems much less extensive than that for oat crown rust.
Barley crown rust can infect rye as well as barley. In addition, it also infects a number of grasses in nature including quackgrass (Elytrigia repens), slender wheatgrass (Elymus tranchycaulus), western wheatgrass (Pascopyrum smithii), foxtail barley (Hordeum jubatum), and several wheatgrasses (Elytrigia spp.) and wild rye grasses (Elymus spp. and Leymus spp.). The fungus readily forms telia on these hosts, which serve as a reservoir of overwintering teliospores. Quackgrass may be the most important reservoir for overwintering telia. This ubiquitous, perennial weed is very susceptible to the rust and is often found growing near Rhamnus.
Developing effective control strategies will depend upon how important this disease becomes in barley production. As with other cereal rust diseases, resistant cultivars will probably provide the most effective and economical control. Sources of resistance to crown rust have been identified in barley germplasm from diverse regions, but most malting barley cultivars currently grown in the northern Great Plains of North America are susceptible to crown rust. It is too early to know how quickly new races of barley crown rust may arise, but experience with oat crown rust suggests that the barley crown rust fungus may be able to overcome race-specific resistance quite rapidly.
Jin, Y., Steffenson, B. J., Oberthur, L. E., and Baenziger, P. S. 1992.
Puccinia coronata on barley. Plant Dis. 76:1283.
Jin, Y., and Steffenson, B. J. 1993. Natural occurrence of barley crown rust
on forage grasses in North Dakota and its pathogenicity on gramineous
species. Phytopathology 83:884.
Jin, Y., Steffenson, B. J., Wesenberg, D. M., and Bockelman, H. E. 1993.
Reaction of Triticum species and related genera to barley crown rust.
Jin, Y. and B.J. Steffenson. 1999. Puccinia coronata var. hordeivar. nov:
morphology and pathogenicity. Mycologia 91:877-884.
Jin, Y. and B.J. Steffenson. 2002. Sources and genetics of crown rust
resistance in barley. Phytopathology 92:1064-1067.
Argrama, H., L. Dahleen, M. Wentz, Y. Jin, and B. Steffenson. 2004. Mapping
molecular markers linked to crown rust resistance gene Rpc1 in barley.
Contact at Cereal Disease Laboratory:Dr. Yue Jin