| Puccinia coronata | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Phylum: | Basidiomycota |
| Class: | Urediniomycetes |
| Subclass: | Incertae sedis |
| Order: | Uredinales |
| Family: | Pucciniaceae |
| Genus: | Puccinia |
| Species: | P. coronata |
| Binomial name | |
| Puccinia coronata Corda, (1837) |
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| Synonyms | |
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Aecidium crassum Pers., (1801) |
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Puccinia coronata is a plant pathogen and causal agent of oat crown rust and barley crown rust. The pathogen occurs worldwide infecting both wild and cultivated oats. It is a relatively new disease of barley in North America. It was first found in 1992 in a barley breeding nursery near Clay Center, Nebraska.[1] 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 posed a threat to barley production, because the first infections in barley occur early in the season from local inoculum.[2]
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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.[2]
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. [2]
Barley crown rust can infect rye as well as barley. In addition, it also infects a number of wild grasses 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.
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. [2] Typically P. coronata can overcome resistant gene within five years, making it difficult for researchers to control its damaging effects on the oat production industry. Agricultural Research Service researchers have introduced individual genes that produce proteins believed to recognize crown rust and trigger a defensive response within the plant. [1] Because of P. coronata’s quick ability to adapt to resistant strains of oat, researchers have had to turn to a new variety of oat (Avena barbata), which is commonly considered a weed, for new resistant genes. In lab studies A. barbata has done remarkably well in conferring resistance to various strains of crown rust. The main goal of the researchers is to not only confer resistance to crown rust, but also to develop oat varieties with additional desirable traits such as high yield and drought tolerance. [3]