Resistance to leaf rust in 26 Mexican wheat cultivars

CIMMYT germplasm derived wheat (Triticum aestivum L.) cultivars are grown on a large area worldwide. The status of leaf rust Puccinia recondita Roberge ex Desmaz. f. sp tritici resistance in various cultivars is unknown. In this study, designated Lr genes were postulated in 26 cultivars released in Mexico between 1950 and 1989 by inoculating their seedlings with 14 pathotypes of diverse avirulence-virulence combinations. The adult plat resistance was evaluated with two currently predominant pathotypes during 1991-1992 crop cycle of Ciudad Obregon in northwest Mexico. Additionally, the probable presence of Lr13 and Lr34 was identified by determining the presence of linked genes Ne2 and Ltn, respectively. Eight Lr genes were present either singly or in combination: Lrl ( in 12 cultivars), Lr3 (4), Lr13 (18), Lr16 (1), Lr17 (3), Lr23 (2), Lr26 (1), and Lr34 (13). Virulence existed for the above genes, except Lr34. The 13 cultivars with Lr34 displayed low to intermediate adult plant disease severities and reduced area under the disease progress curve (AUDPC). Variation in the adult plant disease responses of these cultivars indicated the presence of additional genes for resistance. Lr34 has provided durable leaf rust resistance since the release of Yaqui 50. Several other cultivars lacking Lr34 also displayed reduced ADUPC. A complete database on leaf rust resistance genes in Mexican wheat cultivars has use in increasing genetic diversity in cultivars currently grown. Furthermore, based on the present information additional useful genes can be incorporated in the new germplasm.