QUANTITATIVE TRAIT LOCI INFLUENCING PROTEIN AND STARCH CONCENTRATION IN THE ILLINOIS LONG-TERM SELECTION MAIZE STRAINS

A study was initiated to determine the number, chromosomal location, a nd magnitude of effect of QTL (quantitative trait loci or locus depend ing on context) controlling protein and starch concentration in the ma ize (Zea mays L.) kernel. Restriction fragment length polymorphism (RF LP) analysis was performed on 100 F3 families derived from a cross of two strains, Illinois High Protein (IHP), X Illinois Low Protein (ILP) , which had been divergently selected for protein concentration for 76 generations as part of the Illinois Long Term Selection Experiment. T hese families were analyzed for kernel protein and starch in replicate d field trials during 1990 and 1991. A series of 90 genomic and cDNA c lones distributed throughout the maize genome were chosen for their ab ility to detect RFLP between IHP and ILP. These clones were hybridized with DNA extracted from the 100 F3 families, revealing 100 polymorphi c loci. Single factor analysis of variance revealed significant QTL as sociations of many loci with both protein and starch concentration (P < 0.05 level). Twenty-two loci distributed on 10 chromosome arms were significantly associated with protein concentration, 19 loci on 9 chro mosome arms were significantly associated with starch concentration. S ixteen of these loci were significant for both protein and starch conc entration. Clusters of 3 or more significant loci were detected on chr omosome arms 3L, 5S, and 7L for protein concentration, suggesting the presence of QTL with large effects at these locations. A QTL with larg e additive effects on protein and starch concentration was detected on chromosome arm 3L. RFLP alleles at this QTL were found to be linked w ith RFLP alleles at the Shrunken-2 (Sh2) locus, a structural gene enco ding the major subunit of the starch synthetic enzyme ADP-glucose pyro phosphorylase. A multiple linear regression model consisting of 6 sign ificant RFLP loci on different chromosomes explained over 64% of the t otal variation for kernel protein concentration. Similar results were detected for starch concentration. Thus, several chromosomal regions w ith large effects may be responsible for a significant portion of the changes in kernel protein and starch concentration in the Illinois Lon g Term Selection Experiment.