Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2000
Publication Date: N/A
Interpretive Summary: Oat crown rust is the most serious disease of oat in North America. Breeding resistant varieties is the most economical way to minimize yield losses to crown rust, which may exceed 15% in Midwestern states in severe epidemics. But breeding for crown rust resistance is complicated by the very large number of pathogenic races of the crown rust fungus in North America. Resistance to one rust race is not necessarily effective against another. Communication between plant pathologists and plant breeders in the U.S., Canada, and Mexico has been hampered by the lack of a unified system of identifying races of the crown rust fungus. Therefore, oat breeders have not always gotten clear information about which crown rust races are most important in various regions of North America, and plant pathologists have had difficulty tracking changes in races in crown rust populations. We selected 16 oat lines with distinct resistance types that are most useful for distinguishing different pathogenic races of oat crown in North America. We also developed a four-letter code to name races based on their specific patterns of virulence or lack of virulence on each of the 16 oat lines. This system of identifying oat crown rust races will be used uniformly in the U.S., Canada, and Mexico. Most of the 16 oat lines chosen are being used by oat breeders in North America in developing crown rust resistant varities. The new system will improve the efficiency of resistance breeding as well as facilitating other research on oat crown rust. Therefore, it will help to reduce yield losses to this major oat disease.
Technical Abstract: A nomenclature system for designating virulence combinations of oat crown rust (causal agent Puccinia coronata f. sp. avenae) isolates is proposed. Sixteen oat lines, with seedling resistance genes Pc38, 39, 40, 45, 46, 48, 50, 51, 52, 54, 56, 58, 59, 62, 64, and 68 occurring singly in each of them, are used as primary differentials. The host lines are arranged into groups of four (subset 1 = Pc40, 45, 46, 50; subset 2 = Pc38, 39, 48, 68; subset 3 = Pc51, 52, 58, 59; subset 4 = Pc54, 56, 62, 64). Avirulence and virulence of isolates on each line are indicated by low and high infection types, respectively. The consonants B through T are used to indicate the 16 possible infection type patterns on each subset. Virulence combinations are assigned with a four-letter code for designating races of P. coronata f. sp. avenae. Local differential series are separated from the Pca code by a slash, followed by a listing of the ineffective host genes in the local differentials on which the race was virulent. This system, designated as Pca [for P. coronata f. sp. avenae] code, is similar to the nomenclature system in use for P. graminis (Pers.) f. sp. tritici and P. triticina.