Abstract only

Breeding wheat with durable resistance to important diseases and pests remains a major goal for CIMMYT and various breeding programs worldwide. ?Boom-and-bust? continues to be common for the three rusts and powdery mildew due to the reliance on race-specific resistance genes and their improper deployment. To achieve resistance durability, our strategy is to utilize multiple slow rusting resistance genes that have additive effects. Although various genomic regions are reported to harbor quantitative resistance genes of minor to intermediate effects, only few genes are characterized. The characterized genes often have pleiotropic effects on multiple rusts and other diseases as shown by various studies involving Lr34/Yr18/Sr57/Pm38/Sb1/Bdv1, Lr46/Yr29/Sr/Pm39, Lr67/Yr46/Sr55/Pm46 and Sr2/Yr30. High yielding wheat germplasm with high levels of resistance to all three rusts, including Ug99 race group of stem rust fungus, was successfully developed at CIMMYT by conducting selection in field under high disease pressures. We used a Mexico-Kenya shuttle breeding approach that allowed simultaneous selection for all three rusts. A selected-bulk selection scheme was necessary to retain a large number of plants in segregating generations and shuttling of these populations at various field sites between Mexico and Kenya. Simultaneous progress was also made for resistance to necrotrophic fungi that cause Septoria tritici blotch, tan spot and spot blotch diseases. Although progress is made for resistance to head scab, resistant to moderately resistant wheat varieties and improved wheat germplasm were largely developed through conventional approaches and molecular breeding remains a challenge despite the identification of various genomic regions that have minor resistance genes. At worldwide level, marker-assisted breeding, or other genomic approaches, are either not used by wheat breeders, or utilized for parental characterization, targeted incorporation (often backcrossing) of a few genes and their combinations. This is due to the unavailability of reliable markers for most resistance genes, high cost, and lack of molecular scientists in the breeding team as a majority of the wheat breeding programs operate with limited resources. To make significant impacts, reliable and low cost molecular marker platform that can provide genotypic data for a number of genes must be developed for a successful adoption of molecular breeding. Genomic selection, a novel approach, is being found to be beneficial for simultaneous selection for multiple quantitative traits including complex disease resistance, however deploying the theoretical concept and proof-of-concept studies to a major breeding program will require significantly enhanced financial and human resources. Given the current research investments in wheat, most breeding programs worldwide are expected to continue using mostly conventional field based approaches or limited marker assisted breeding.

Global Wheat Program

English

Lucia Segura

INT0610|INT2833|INT2843|INT2868|INT3206|INT3524|INT3297

CIMMYT Staff Publications Collection