Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2010
Publication Date: 5/1/2010
Citation: Jin, Y., Szabo, L.J., Carson, M.L. 2010. Century-old Mystery of Puccinia striiformis Life History Solved with the Identification of Berberis as an Alternate Host. Phytopathology. 100(5):432-435.
Interpretive Summary: Stripe rust is one of several economically important diseases of cereal crops and grasses in the U.S. and worldwide. The causal agent of stripe rust is the fungus, Puccinia striiformis. Cereal rust fungi have complex life histories that involve two different hosts. However, the alternate or aecial host on which the sexual cycle is completed has remained a mystery. In contrast, the life histories for other cereal rust fungi were elucidated over a century ago. Using inoculation studies and DNA analysis, barberry species (Berberis) was proven to be an alternate host for the stripe rust pathogen. Puccinia striiformis is known to be one of the most variable cereal rust pathogens with regard to virulence. Many new races are regularly identified in wheat producing areas where stripe rust is a major disease. This variability in virulence has been attributed to mutations and somatic hybridization since the sexual stage was presumed to be absent. The discovery of an alternate host suggests that in areas where wheat and susceptible barberry species coexist, sexual recombination has likely played an important role in contributing to pathogen variability and the breakdown of resistance in wheat. This discovery will provide a powerful tool to rapidly advance our knowledge on the genetics of the stripe rust fungus, and lead to the development of improved strategies for a better control of stripe rust.
Technical Abstract: The life history of Puccinia striiformis remains a mystery because the alternate host has never been found. Inoculation of grasses using aeciospores from naturally infected Berberis chinensis and B. koreana resulted in infection on Poa pratensis, producing uredinia typical of stripe rust caused by P. striiformis. Analyses using Real-time PCR and DNA sequence confirmed the rust fungus as P. striiformis. Pycnia and aecia were produced on B. chinensis, B. holstii, B. koreana, and B. vulgaris after inoculation using telia of P. striiformis f. sp. tritici, demonstrating that Berberis spp. also serve as the alternate host for wheat stripe rust pathogen.