MORPHOLOGY AND COMBINING ABILITY STUDIES OF MAIZE POPULATIONS RECOVERED FROM THE INTERGENERIC CROSS ZEA X TRIPSACUM

The extent, diversity and breeding potentials of gene transfers betwee n 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) com binations with inbreds 0h43, Mo17, and B73. Variance, correlation, ste pwise multiple regression, and diallel analyses were used to different iate populations. Polyacrylamide electrophoresis performed on BC popul ations A, B (tripsacoid), and C (maizoid) suggests genetic transfer fr om Tripsacum. Morphological studies show that the populations selected not only differ but also that they could be maintained during five ge nerations for the intended kind and degree of tripsacoidy. Is was poss ible to derive a still more tripsacoid population D from population A. Phenotypic variability is greatest among traits indicative for tripsa coidy: length of lateral branches, number of ears, and kernel thicknes s decrease towards more maizoid introgression, whereas ear length, ker nel number/ear, pith diameter, kernel and ear volumes increase in this direction. Correlation matrices show kernel thickness negatively corr elated with eitht ear and kernel traits for maizoid population C, whil e 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 respo nse models for dependent trait kernel number/ear. Diallel analyses sho w significant differences due to general combining ability for prolifi cacy and ear length in BC's of populations A and B, and C respectively , with B73. Traits for significant specific combining ability are grai n yield, prolificacy and ear length. The upper 17 diallel crosses aver aged 5,225 kg/ha as compared to hybrid check's average yield of 5,417 kg/ha. Evidence points to B73 as the best inbred for maintenance of tr ipsacoid gene transfers during the described back-cross program. The s uccessful controlled introgression procedure may encourage breeders tr ying to enrich the primary maize gene pool with different traits for p lant architecture, floral and reproduction biology, and disease, pest, and drought resistance from Tripsacum.