COMBINING ABILITY FOR TEST WEIGHT AND AGRONOMIC TRAITS OF OAT

The relative importance of additive and nonadditive variation for agronomic traits provides guidelines for setting breeding strategies for cultivar development. To estimate the relative importance of general and specific combining ability (GCA and SCA) for five traits of oat (Avena sativa L.), 24 oat genotypes were mated according to a Design II scheme. The 24 parents were a sample from elite germ-plasm available for cultivar development at Iowa State University and in various regions of the USA. Test weight, grain yield, harvest index, date of heading, and plant height were measured for 10 random F2-derived F3 lines from each of 95 crosses. The oat lines were evaluated in 1988 in four replicates at each of three locations in Iowa. Both GCA and SCA were significant (P less-than-or-equal-to 0.01) for all traits; GCA, however, accounted for 75% of the variability among crosses for test weight, 85% for grain yield, 82% for harvest index, 72% for date of heading, and 85% for plant height. We speculate that additive X additive epistasis was primarily responsible for the observed significant SCA because the estimate of SCA represents 1/4 sigma(D)2 + 1/2 sigma(AA)2, and in our experiment sigma(D)2 seemed small (based on contrasts of parent vs. offspring means). We suggest that breeders use mild selection intensities in early generations of inbreeding to avoid discarding lines before favorable epistatic combinations form. In regard to parent selection, our results indicate that most parents could be used as male or female in a cross without affecting segregation for these five traits; however, midparent values alone do not adequately predict which crosses produce the most outstanding lines.