Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2004
Publication Date: 1/1/2005
Citation: Leonard, K.J., Anikster, Y., Manisterski, J. 2005. Virulence associations in oat crown rust. Phytopathology. 95:53-61. Interpretive Summary: Crown rust, the most destructive disease of oat, is difficult to control. Most resistance in oat is race-specific. Extensive use of any single resistance in commercial oat production selects virulent rust races that can overcome that resistance. Virulence to overcome most known genes for crown rust resistance already exists to some extent in the U.S. oat crown rust populations, but few strains of crown rust have combined virulence to most of the known resistance genes. We studied oat crown rust populations on cultivated oat in TX, MN, ND, SD, and on wild oat in Israel, which was the source of most crown rust resistance currently used in the U.S. Our goal was to determine whether some virulence combinations are more difficult than others for the rust fungus to maintain. We found four groups of four to six virulence genes each that were consistently associated in crown rust in the U.S. and Israel. Virulence genes in one group of five genes showed limited ability to combine with virulence from the other three groups. Resistance gene combinations in current oat varieties often match virulences within a single virulence group that combine naturally in the crown rust fungus. By combining resistance genes that correspond to virulence genes from opposing virulence groups, it may be possible to produce new oat cultivars with more durable resistance. This could be accomplished readily in traditional breeding programs without the need for advanced technological breakthroughs. The result will be more productive oat varieties that suffer less yield and quality reduction due to crown rust.
Technical Abstract: Isolates of Puccinia coronata obtained from natural populations of Avena sterilis in Israel, winter oat (A. sativa) cultivars in Texas, and spring oat cultivars in the Northern Plains States of Minnesota, North Dakota, and South Dakota were analyzed for significance of pair-wise virulence associations. Isolates from all three regions were tested on 25 oat lines with single Pc genes for crown rust resistance from A. sterilis and one line with a Pc gene from A. sativa. Isolates from Israel were tested also on 11 Iowa backcross lines with undesignated crown rust resistance genes from A. sterilis. Four associated virulence groups were identified from significant positive virulence associations that were consistent across all three regions. Group 38 included virulence to Pc-38, 39, 55, 63, and 71; Group 45 included virulence to Pc-45, 46, 48, 52, 54, and 57; Group 58 included virulence to Pc-35, 40, 58, and 59; and Group 61 included virulence to Pc-36, 51, 56, 60, and 61. Virulence to Pc-70 showed the strongest association to virulences in Group 38 but also showed significant association with virulence to Pc-45, 35, and 58. Virulences in Group 61 were consistently negatively associated with virulences in Group 38 in each region. In Israel, virulences to five of the Iowa lines showed positive associations to virulences in Group 61 and negative associations to virulences in Groups 38 and 45. Close similarity of reactions of nearly all isolates to Pc-39, 55, and 71 suggest that these genes may be identical or nearly identical alleles.