Morphology and combining ability studies of maize populations recovered from the intergeneric cross Zea x Tripsacum

Abstract

The extent, diversity and breeding potentials of gene transfers between maize and gama grass were investigated. The original cross Zea mays x Tripsacum dactyloides (2n = 72) was followed by seven backcrosses to several maize pollen sources resulting in a recovered maize bulk (2n = 20). Four populations ranging from highly tripsacoid to maizoid were derived through selection. They were studied for grain yield plus 17 plant and ear characters, either per se or in F₁ or backcross (BC) combinations with inbreds OH₄₃, Mo 17, and B73. Variance, correlation, stepwise multiple regression, and diallel analyses were used to differentiate populations. Polyacrylamide electrophoresis performed on BC populations A, B (tripsacoid), and C (maizoid) suggests genetic transfer from Tripsacum.
Morphological studies show that the populations selected not only differ but also that they could be maintained during five generations for the intended kind and degree of tripsacoidy. Is was possible to derive a still more tripsacoid population D from population A.
Phenotypic variability is greatest among traits indicative for tripsacoidy: length of lateral branches, number of ears, and kernel thickness decrease towards more maizoid introgression, whereas ear length, kernel number/ear, pith diameter, kernel and ear volumes increase in this direction.
Correlation matrices show kernel thickness negatively correlated with eitht ear and kernel traits for maizoid population C, while corresponding correlations for tripsacoid populations A, B and D are mostly non-significant or positive. Differences between populations C and D are strikingly obvious when comparing multiple regression response models for dependent trait kernel number/ear. Diallel analyses show significant differences due to general combining ability for prolificacy and ear length in BC's of populations A and B, and C respectively, with B73. Traits for significant specific combining ability are grain yield, prolificacy and ear length. The upper 17 diallel crosses averaged 5,225 kg/ha as compared to hybrid checks's average yield of 5,417 kg/ha. Evidence points to B73 as the best inbred for maintenance of tripsacoid gene transfers during the described back-cross program.
The successful controlled introgression procedure may encourage breeders trying to enrich the primary maize gene pool with different traits for plant architecture, floral and reproduction biology, and disease, pest, and drought resistance from Tripsacum.