IDENTIFICATION OF QUANTITATIVE TRAIT LOCI USING A SMALL SAMPLE OF TOPCROSSED AND F4 PROGENY FROM MAIZE

Plant breeders have an interest in the identification of genomic regio ns associated with the expression of quantitative traits because they recognize that such information could be used to improve realized heri tability and reduce time per cycle of selection. The development of mo lecular marker technologies may provide tools to accomplish these goal s. Maize (Zea mays L.) breeders develop new inbred parents of hybrids through topcrossed and per se evaluation of numerous quantitative trai ts in segregating progeny from planned breeding crosses. This study wa s conducted to determine if regions of the genome associated with vari ability of agronomically important traits could be identified by a sma ll, but typical, sample of topcrossed and F-2:4 progeny from the cross B73xMO17. We identified genomic regions in 24 agronomic traits, using interval mapping and simultaneous estimation of multiple quantitative trait locus models. The estimated numbers of quantitative trait loci (QTL) identified per trait were about three to five. Many of the ident ified QTL were the same for correlated traits. Interestingly, yield QT L were not in the same regions previously reported for B73xMO17. This comparison contains a number of potential confounding factors: source of parental inbreds, type of progeny, different genotype x environment interaction effects, and different small samples of progeny from the cross. Consideration of these factors and the power of the tests to id entify QTL suggests that the sampling of progeny is the most likely ex planation for the differences.