Evaluation of reciprocal recurrent selection composites for combining ability and phenotypic variability

Abstract

During 1963 and 1964 composites from a reciprocal recurrent selection breeding program were evaluated to determine the effectiveness of the program in improving combining ability and maintaining phenotypic variability within the populations. The combining ability tests were grown at College Station and Temple, Texas. Composites were available from five cycles of testing of the reciprocal recurrent selection study being conducted by the Texas Agricultural Experiment Station. The open-pollinated varieties Yellow Surcropper (YS) and Ferguson's Yellow Dent (FYD) are the parental varieties in the study. Crosses were made in all possible combinations with the YS composites and the FYD composites, i.e. YS-0 x FYD-0, FYD-1, FYD-2, etc. Crosses also were made with the composites, YS-0 to YS-4 and FYD-0 to FYD-4 and seven testers. The results of this study indicated that general combining ability was relatively more important than specific combining ability in determining the characters studied. However, since composites rather than homozygous lines were used in this study, there was probably a better estimate of general combining ability than of specific combining ability. The yields of the composite crosses and composite x tester crosses indicated that the greatest improvement has been made for general combining ability in the FYD population. Little if any improvement has been made in the YS population. In the variability study, the composites were space-planted in blocks at College Station and Temple. Measurements were made of 200 plants of each composite at each location. Variances were computed for each composite and the variances within each group for each location were tested for homogeneity using Bartlett's test for homogeneity of variances. Variation, as measured by the variance of the composites, has been maintained at a high level for all agronomic characters studied. In the YS group a decrease in variation occurred for ear length and ear weight, while in the FYD group, variation of ear length, rows per ear and ear weight was reduced. In the YS group selection for yield resulted in an increase in number of days to silk, plant height, ear height, rows per ear and ears per plant. In the FYD group selection for yield resulted in altering the number of days to silk, ears per plant, ear circumference and ear weight. Ear circumference, ear weight and ear length were affected in a negative manner while the other characters were affected in positive manner.