More than 12% of maize productivity is lost to diseases annually in Asia. Sources of resistance to several important diseases have been identified in advanced CIMMYT germplasm but the genetics of resistance is poorly understood. Disease resistance in maize is reported to be conditioned by both major (qualitative) genes and minor (quantitative) genes or quantitative trait loci (QTL). To date, 437 quantitative disease resistance loci or dQTL, 17 major resistance genes and 25 resistance gene analogs (RGAs) associated with resistance to 11 maize diseases have been described in a few of these sources. QTL mapping studies conducted in maize thus far have provided information on the genetic architecture of disease resistance including the number, location and action of chromosomal segments conditioning the trait. The availability of the maize genome sequence offers new opportunities for a detailed understanding of the organization and architecture of disease resistance, fine mapping of QTL, validating candidate genes and identifying effective molecular markers to improve disease resistance. However, full exploitation of genomic approaches and information to develop and release maize cultivars more resilient to diseases will only be possible through (i) a deeper integration of genomic approaches with conventional breeding methodologies; (ii) a capacity to reliably and accurately phenotype diseases on a large scale; and (iii) a sound multidisciplinary knowledge of the biochemical and physiological processes determining crop yield and its stability under different disease stress regimes. A major emphasis for the Asian region will have to include the collaborative evaluation of promising sources of resistance for specific traits using standardized protocols that would allow harmonization of disease phenotypic data for use in identifying the most promising resistance genes, validating molecular markers liked to effective dQTL and major resistance genes and incorporation of the most promising sources in improvement activities.

Global Maize Program

English

Lucia Segura

INT2822