Gene action, combining ability, heterotic grouping and hybrid performance of tropical maize inbred lines from a public breeding program in Brazil
Introduction Single-cross hybrids are the predominant type of cultivar planted by maize growers worldwide. The clear understanding of both the inheritance of target traits and the heterotic patterns of breeding germplasm is essential for the development of heterotic and high-yielding single-cross hybrids in maize breeding programs. Therefore, our objectives were to determine the inheritance of agronomic traits in improved tropical maize germplasm; estimate the general and specific combine abilities (GCA and SCA) effects for these traits among 15 selected inbred lines; group these lines into heterotic groups using two approaches; and identify high-yielding hybrids derived from these lines. Methods We evaluated 105 F1 single-cross hybrids derived from crossing among the 15 selected inbred lines using diallel mating design, along with five checks commercial hybrids, for a wide range of agronomic traits over three summer seasons in southeastern Brazil. A mixed model approach was used to estimate the variance components of GCA and SCA, to predict the GCA and SCA effects, and also to obtain adjusted means of the hybrids. Results and discussion We found that the inheritance of most traits is predominantly governed by additive gene action, whereas grain yield is largely modulated by non-additive gene action in our set of selected inbred lines of tropical maize. The lines VML016, VML062, VML081, VML083 and VML131 are promising for simultaneously improving GY and reducing cycle and plant stature, whereas the VML105 and VML157 should be used to reduce cycle and increase grain yield, respectively, in our maize breeding program. Both the genetic distance among lines and the SCA effects for GY are effective for grouping the improved breeding lines into genetically distinct groups. Also, molecular makers should be employed to support the allocation of inbred lines into heterotic groups and aid in the selection of the best parental combinations for the development of breeding populations and hybrids in improved tropical maize germplasm. Finally, we identified 13 outstanding experimental hybrids that must be evaluated to confirm the consistence and stability of their yield performance across a wider range of environments and management conditions in southeastern Brazil for future release and commercialization.