Diallel Analysis of Relative Growth Rates in Maize Synthetics

Abstract

Previous studies indicated that relative growth rates (RGR) based on easily obtained measurements [(leaf number ✕ leaf length ✕ leaf width ✕ O.5)/days to silking] hold promise as a selection tool to increase grain yields in early‐maturing maize (Zea mays L.). The objective of this field research was to evaluate the interrelationships among RGR, grain yield, yield components, and components of RGR. Three independent diallel sets among eight parental synthetics were evaluated in up to nine environments during 3 yr. General combining ability (GCA) and specific combining ability (SCA) effects were estimated using Griffing's Method 4, Model 1. Correlations among GCA effects (rA) for all traits were obtained. Mean squares for GCA were highly significant for all traits in one or more of the diallels, while SCA effects were significant in 50% of the F‐tests. The relative magnitudes of ratios ef the GCA component to GCA pros SCA components (mean squares) suggested that it should be easier to select parents of high‐performing progenies for kernel row number, kernel weight, RGR, leaf length, and silking date than for kernels per row or grain yield. Correlations among GCA effects estimated across environments for three diallels among eight synthetics indicated that GCA effects for RGR were highly correlated (rA = 0.82) with GCA effects for grain yield. Highly significant correlations among GCA effects for RGR, ears per plant, and kernels per row (primary yield components), as well as highly significant correlations among GCA effects for yield and leaf number, leaf length, and days to silking (RGR components), indicated that these traits are not independent. Results confirmed the suggestion that selection for increased RGR would increase grain yields in early maize.