Monday, November 13, 2006

Validation and Characterization of Candidate Resistance QTL for Marker-Assisted Selection of Resistance to Multiple Foliar Pathogens of Maize.

Richard Pratt1, Godfrey Asea2, Patrick Lipps2, Bingiganavile Vivek3, and George Bigirwa4. (1) Ohio State University - OARDC, Dept of Horticulture & Crop Science, 1680 Madison Ave., Wooster, OH 44691, (2) The Ohio State Univ, Dept of Horticulture & Crop Science, 1680 Madison Ave., Wooster, OH 44691, (3) CIMMYT, P.O. Box MP163, Mt. Pleasant, Harare, Zimbabwe, (4) Namulonge Agricultural and Animal Production Research Institute, P.O. Box 7084, Kampala, Uganda

Maize production in sub-Saharan Africa is often adversely affected by Northern corn leaf blight (NCLB), gray leaf spot (GLS) and maize streak foliar diseases. We were interested in determining the utility of molecular markers linked to consensus QTL for NCLB and MSV resistance, and to newly reported QTL for GLS resistance, for improving selection efficiency. We developed flanking SSR markers to examine QTL for NCLB in three consensus regions (chromosomal bins); one consensus MSV QTL; and two GLS QTL; as potential targets for selection. Partially inbred progenies derived from parents with complementary resistance QTL were evaluated for each disease during two seasons. Narrow-sense heritability and gene action of the candidate QTL were determined. For NCLB, resistance due to the presence of alleles from QTL in bins 3.06 and 5.04 were detected across two seasons. The chromosomal region in bin 4.08 for GLS resistance was significant across seasons using late-season disease assessments. The major QTL (bin 1.04) conferring resistance to MSV was significant for resistance across seasons and explained 23% of phenotypic variations in the F2:4 generation. Phenotypic values associated with flanking markers at each locus based on interval analysis indicated that QTL in bin 4.08 for GLS, bin 1.04 for MSV, and bins 3.06 and 5.04 for NCLB significantly reduced disease severity. Our results validated the position and effect of four out of six QTL reported to condition partial resistance to these pathogens. The lack of confirmation of two QTL points out the need for validation of resistance loci in new breeding populations. The QTL confirmed in this study should contribute to positive genetic gain if used in a marker-assisted breeding program.