Quantitative Genetic Analysis of Grain Filling Rate and Grain Filling Period in Tropical Maize (Zea Mays L.)

Abstract

Grain yield of maize in the tropics is limited by short days and high temperatures. Genetic information on grain filling rate (GFR) and grain filling period (GFP) in tropical maize germplasm is limited. The objectives of this study were to (1) determine genetic variation and genotype by month interactions (G x M) for GFR, GFP, chlorophyll concentration (SPAD) and other agronomic traits, (2) estimate general combining ability (GCA), specific combining ability (SCA) effects and the interactions of GCA and SCA with months for the aforementioned traits, (3) estimate non-allelic interactions for GFR and GFP using generation mean analysis (GMA), (4) determine genetic relationships among GFR and GFP with other agronomic traits, and (5) determine the effects of photosynthetic active radiation (PAR) and temperature on GFR, GFP and other agronomic traits. Eight elite tropically adapted maize inbreds and their 28 diallel hybrids were planted in four different months in Waimanalo, Hawaii. Two GMA populations representing GFR and GFP were also planted in two Waimanalo months. Significant differences occurred among inbreds, hybrids, heterosis, G x M, GCA, SCA, GCA x M and SCA x M interactions for GFR, GFP and SPAD. Additive genetic effects were the most prevalent type of gene action for GFR, GFP, and SPAD as shown by higher ratios of GCA to SCA mean squares. The GMA analyses of GFR and GFP data revealed little convincing evidence of departure from a simple model of additive and dominance variance, without compelling gene interactions. In some cases, the additive x dominance interactions were significant for GFR and the dominance x dominance interactions significant for GFP. Estimates of the genetic effects were mostly confounded with the interaction components and the environment. Kernel weights were highly correlated with GFR indicating that it may be used as an effective selection index for GFR. Photosynthetic active radiation accounted for most of the variation in GFR, GFP, kernel weight, plant yield and kernel numbers. Breeding approaches that take advantage of additive variances including hybrid breeding with evaluations in multiple environments may be used to alter GFR, GFP and chlorophyll concentration in tropical maize germplasm.