Genetic analyses of grain-filling rate and duration in maize

Grain-filling rare and duration influence grain yield in maize (Zea mays L.), but very little information on their inheritance exists. To devise effective breeding strategies, the genetic nature of these traits must be understood. The objectives of this study were to (1) examine general combining ability (GCA) and specific combining ability (SCA) for grain-filling rate, grain-filling duration, and related agronomic traits via North Carolina Design Il, (2) determine the inter-relationships among these traits and their influence on yield via correlation and path coefficient analyses, and (3) identify an indirect selection criterion for yield. Design II crosses among four inbred lines used as males and a set of four inbred lines as female parents were grown in 1996. Combining ability analyses indicated that both GCA (Vg) and SCA mean squares (V-s) were significant for grain-filling rate (on a kernel or an ear basis) and effective filling duration. General combining ability was more important than SCA for both kernel-filling rate and effective filling duration, whereas SCA effect was more important for ear-filling rate: The ratio 2V(g)/(2V(g) + V-s) was 0.85, 0.88, and 0.45 for kernel-filling rate, effective filling duration, and ear-filling rate, respectively. Kernel-filling rate had a positive phenotypic correlation with kernel weight and was negatively correlated with midsilk date and effective Filling duration. Kernel number per ear was more important than kernel-filling rate in influencing grain yield. These relationships were confirmed by results from a 1997 experiment using nine commercial hybrids. Chlorophyll readings taken with SPAD chlorophyll meter at a late developmental stage gave a positive genetic correlation with single-plant yield (r = 0.73). A path coefficient analysis revealed that chlorophyll concentration had a small direct effect on grain yield, whereas it had a large indirect effect on grain yield via kernel number per ear and grain-filling duration. Kernel weight and midsilk date could serve as indirect selection criteria for effective grain-filling duration and kernel-filling rate. Chlorophyll concentration at a late developmental stage could also be an indirect selection criterion for final grain yield. (C) 1999 Elsevier Science B.V. All rights reserved.