MEXICAN OAT GERM PLASM AS A SOURCE OF RESISTANCE TO STEM RUST AND CROWN RUST

One hundred and three lines and cultivars of oat used as progenitors i n the oat breeding programs in Chihuahua and Chapingo, Mexico, were te sted for resistance to stem rust and crown rust. Each line or cultivar was evaluated in the seedling stage to races NA8, 16, 25, 26, 27, 28, and 55 of Puccinia graminis f. sp, avenae (stem rust), and isolates C R13, 20, 36, 50, 152, and 169 of P. coronata f. sp. avenae (crown rust ). Additional tests were performed on crown rust resistant lines with isolates CR185 and CR225. The same material was tested in the adult pl ant stage in field nurseries inoculated with a composite of the above rust isolates, except for NA26. Of the 103 lines evaluated in the seed ling stage to stem rust, 32 were resistant to all races except NA28, i ndicating the presence of gene Pga. The presence of genes Pg2 + Pg9, P ga + Pg9, Pg4, and Pg13 were indicated in 15, 9, 1, and 4 lines, respe ctively. In the remaining 41 lines, the identity of possible resistanc e genes could be determined from the seedling tests. The field tests i ndicated the presence of the adult plant resistance gene Pg11 in 22 of the lines. Twenty eight lines were detected with seedling resistance to crown rust. Of these, 8 lines may contain gene Pc59. The results in dicate the presence of potentially useful sources of resistance, warra nting further genetic studies to confirm these preliminary findings.