Differences Between Reciprocal Crosses of Maize for Kernel Growth Characteristics

Measurement of the length of the grain filling period may become a useful estimator of the yield potential of maize (Zea mays L.) breeding selections, but differences between reciprocal crosses could confound early generation evaluations. The objective of our study was to determine the existence and nature of reciprocal effects for effective filling period (EFP) and kernel growth rate. Four inbred lines were self- and cross-pollinated in all possible combinations and their progenies were self-pollinated to provide reciprocal genotypes for evaluation. The genotypes were grown in randomized complete block designs near Lexington, Ky. for 2 years. Reciprocal differences among the F₁ kernel genotypes were found for both EFP and kernel growth rate. Maternal effects of inbred plants on F₁ kernel genotypes were indicated for EFP but not for kernel growth rate where dosage and dominance effects were present. The F₂ generation kernel analysis indicated that the observed reciprocal differences were not of cytoplasmic origin. Measurements of pericarp weight indicated that the kernel pericarp did not restrict kernel size. EFP's of F₁ kernel genotypes were often greater than those of homozygous kernel genotypes and may have resulted from greater potential of the F₁ genotypes or genetic restrictions of the homozygous genotypes. Dominance, as a result of gene dosage in the endosperm, was observed for kernel growth rate and could have been interpreted as maternal influences had all genotypes not been examined. Genetic analysis of F₂ means showed that EFP and kernel growth rate expressed heterosis in the F₂ kernel generation. Our data suggested that maternal influences are possible on the expression of EFP and that reciprocal differences for kernel growth rate can be caused by dosage effects in the kernel endosperm. Either effect dictates that control of pollination is needed for accurate evaluation of EFP.