Yellow rust (YR) or stripe rust, caused by Puccinia striformis f. sp tritici Eriks (Pst), is a major challenge to resistance breeding in wheat. A genome wide association study (GWAS) was performed using 22,415 single nucleotide polymorphism (SNP) markers and 591 haplotypes to identify genomic regions associated with resistance to YR in a subset panel of 419 pre-breeding lines (PBLs) developed at International Center for Maize and Wheat Improvement (CIMMYT). The 419 PBLs were derived from an initial set of 984 PBLs generated by a three-way crossing scheme (exotic/elite1//elite2) among 25 best elites and 244 exotics (synthetics, landraces) from CIMMYT’s germplasm bank. For the study, 419 PBLs were characterized with 22,415 high-quality DArTseq-SNPs and phenotyped for severity of YR disease at five locations in Mexico. A population structure was evident in the panel with three distinct subpopulations, and a genome-wide linkage disequilibrium (LD) decay of 2.5 cM was obtained. Across all five locations, 14 SNPs and 7 haplotype blocks were significantly (P < 0.001) associated with the disease severity explaining 6.0 to 14.1% and 7.9 to 19.9% of variation, respectively. Based on average LD decay of 2.5 cM, identified 14 SNP–trait associations were delimited to seven quantitative trait loci in total. Seven SNPs were part of the two haplotype blocks on chromosome 2A identified in haplotypes-based GWAS. In silico analysis of the identified SNPs showed hits with interesting candidate genes, which are related to pathogenic process or known to regulate induction of genes related to pathogenesis such as those coding for glunolactone oxidase, quinate O-hydroxycinnamoyl transferase, or two-component histidine kinase. The two-component histidine kinase, for example, acts as a sensor in the perception of phytohormones ethylene and cytokinin. Ethylene plays a very important role in regulation of multiple metabolic processes of plants, including induction of defense mechanisms mediated by jasmonate. The SNPs linked to the promising genes identified in the study can be used for marker-assisted selection.

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The adult plant resistance conferred by genes with an additive effect is an alternative to achieve durable resistance to leaf rust caused by the fungus Puccinia triticina in wheat (Triticum spp.) The objective of this study was to know the response to this disease in bread wheat genotypes that possess the partial resistance genes Lr34, Lr46, Lr67 and Lr68. The severity level of the disease was measured in 280 wheat genotypes in three locations. The presence or absence of partial resistance genes was determined by molecular markers for each gene in 245 wheat genotypes. The different combinations of adult plant genes resulted in the genotypes were classified into nine groups. In 77 of these genotypes, the markers were negative for these genes. The Lr34, Lr46, Lr67 and Lr68 genes were identified individually in 48, 48, 5, and 14 genotypes, respectively. The combination of two genes, Lr34+Lr46, Lr34+Lr68 and Lr46+Lr68, was determined in 18, 17, and 12 genotypes, respectively. Only in six genotypes the combination Lr34+Lr46+Lr68 was identified. The genotypes with the Lr34, Lr46, Lr67 and Lr68 genes in a unique form showed 21%, 24.8%, 21.9% and 21.8% of rust severity on average, respectively. An additive effect was observed in the combinations of two genes, and higher effect in the combinations that included the Lr34 gene since genotypes with this gene combination showed on average 11.4% of rust severity. The combination of three genes Lr34+Lr46+Lr68 provide greater protection in the genotypes with 9.7% of rust severity on average.

En la región de El Bajío un factor que ha afectado la producción de trigo (Triticum spp.) de riego en los últimos 15 años es la poca disponibilidad de agua en las presas, lo que ha provocado que la superficie sembrada durante este periodo haya fluctuado entre 82,912 y 193,966 ha. El programa de trigo del Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias (INIFAP) con sede en el Campo Experimental Bajío (CEBAJ) en Celaya, Guanajuato ha evaluado desde 1992 líneas sobresalientes de trigo bajo calendarios de dos, tres y cuatro riegos, incluido el riego de siembra. En el material segregante se ha practicado selección en forma alternada con tres y cuatro riegos. Esta estrategia de selección ha permitido identificar nuevos genotipos con mayor potencial de rendimiento bajo riego restringido (dos y tres riegos totales), entre ellos la nueva variedad de trigo harinero Elia M2016.