Relationship of parental phenotypic and genotypic differences with progeny genetic variance and heritability in maize

The ability to identify parental combinations that will result in greater progeny genetic variance and heritability would help to maximize genetic gain from selection in plant breeding programs. Similarly, quantitative trait locus mapping projects would be made more efficient if parental combinations resulting in greater progeny genetic variances could be determined before investing resources in mapping population development. Parental phenotypic and genetic differences may be related to progeny genetic variance and heritability. In this study, the use of absolute phenotypic differences (PD) and genetic distances (GD) between parental lines of maize as predictors of the genetic variance component (GVC) and heritability on a per-plot basis (h 2p) of their progeny was investigated.;The genetic material comprised 26 populations of 200 F5:6 recombinant inbred lines (RIL) each. RILs were derived from crosses between inbred line B73 with 26 diverse inbred lines from around the world. The RIL populations plus the parental lines were evaluated for fifteen traits at four environments in the USA. Regression analyses indicated that there was a significant linear relationship between GVC and PD for nine of the fifteen traits. Heritability is different from genetic variance because h2 p includes in its formula the phenotypic variance as denominator. This might cause that the relationship between h2 p and PD was significant only for six of the traits. On the other hand, the range for GD based on SSR markers was narrow (0.66 to 0.90) and the analysis indicated non-significant linear relationships between GVC and GD for most of the traits. The only traits for which the relationship was significant were number of nodes from tassel to ear and plant height. GD was related to progeny heritability only for tassel length, central spike length, leaf length, and upper leaf angle. These results suggest that parental phenotypic differences tend to have a loose positive relationship with progeny genetic variance and can be used as a criterion to select parents for breeding or mapping populations with some success expected. Traits such as flowering time that exhibited a greater relationship between PD and GVC may be controlled by fewer genes, with greater additive gene action than traits like plant height, which had a lower correlation. Genetic distance evaluated by SSR markers may have only limited value for predicting GVC and heritability, as the relationships were significant only in a few of the fifteen traits evaluated in this study. This study had limited power to test the relationship between parental genetic distance and progeny genetic variance, however, because of the limited range of genetic distances between parents used to make the crosses.