P0368 Marker-Assisted Breeding of Downy Mildew Resistant Corn for the Philippines

Hayde F. Galvez , University of the Philippines Los Banos, College, Laguna, Philippines
Arma Kristal B. Malijan , University of the Philippines Los Banos, College, Laguna, Philippines
Alma O. Canama , University of the Philippines Los Banos, College, Laguna, Philippines
Cecilia B. Pascual , University of the Philippines Los Banos, College, Laguna, Philippines
Proceso H. Manguiat , University of the Philippines Los Banos, College, Laguna, Philippines
Reynaldo B. Quilloy , University of the Philippines Los Banos, College, Laguna, Philippines
Mona Liza S. Jubay , University of the Philippines Los Banos, College, Laguna, Philippines
Eden Jane U. Tongson , University of the Philippines Los Banos, College, Laguna, Philippines
Roanne R. Ripalda , University of the Philippines Los Banos, College, Laguna, Philippines
Desiree M. Hautea , University of the Philippines Los Banos, College, Laguna, Philippines
Corn is the second most important (staple) crop in the Philippines. As a standard cultural management, seed-materials are pre-treated with metalaxyl fungicide prior to sowing. Without fungicide seed treatment, and follow-up foliar spray, disease outbreak particularly caused by downy mildew (DM) fungus, Peronosclerospora philippinensis Weston (Shaw), can reduce corn produce to as high as 80-100%. While the availability of metalaxyl-fungicide preparation is being constrained for large-scale application, the Philippine DM has also been reported to develop resistance against this pesticide. 

DM resistance is available in corn germplasm. However, breeding for DM resistant and outstanding corn variety has not been successful through pure conventional means. The use of biotechnology particularly DNA marker has proven efficient to breed for complex trait in major crops including corn e.g. drought tolerance and enhanced protein.  We report the successful application of DNA marker technology to breed for DM resistant outstanding yellow corn variety for the Philippines. Corn microsatellite (SSR and EST-SSR) and resistance gene analog (RGA) markers were successfully used to (a) purify parent lines, (b) re-establish genetic structure of recombinant inbred line (RIL) population for genetic mapping, (c) fine-map DM resistance loci (QTL), (d) develop DM resistance gene-specific marker, (e) approximate combining ability based on genetic distance, and (f) in combined marker-assisted selection breeding (MAB) schemes. Resistance QTL were validated in multi-location DM screening involving the major corn growing regions in the Philippines. Multi-location field resistance, resistance under controlled DM-nursery assay and foreground/background DNA markers were the main basis in selecting the final corn lines and test hybrids for yield trial.  Best performing DM resistant line/hybrid will be released as a registered new corn variety and/or genetic stock. MAB scheme to introgress DM resistance into the white corn germplasm is proposed; as well as MAB pyramiding with the maize quality protein gene.