SELECTION FOR EARLY HEADING AND CORRELATED RESPONSE IN MATURITY OF SOFT RED WINTER-WHEAT

Heading date in wheat (Triticum aestivum L. emend. Thell.) is an easily identifiable trait, and previous research has shown it can be modified. However, several studies have shown that heading date is not always highly correlated with harvest maturity. This study was conducted to gain a more thorough understanding of the relationships between heading date and traits related to maturity such as kernel growth rate (KGR), effective filling period (EFP), and time of physiological maturity. We evaluated direct and correlated response to two cycles of phenotypic recurrent selection for early heading date in two wheat populations in 1989. Direct response to selection for early heading date was -5 and -10 d, respectively, in the two populations. In Population 1, correlated response to selection was not significant. We observed a significant reduction in mean KGR from 2.56 to 2.13 mg kernel-1 d-1 from the C0 to the C2 in Population 2, with no significant change in mean EFP. Heritability estimates ranged from 0.10 for yield in population 1 to 0.81 (P < 0.01) for heading date in Population 2. Mean estimated date of physiological maturity (EPM) was significantly reduced in both populations after two selection cycles. Early EPM of the C2 apparently reflected an early heading date and not a reduced grain filling period. However, the earliest heading entries were not always the first to reach EPM. Thus we suggest a maturity rating based on EPM in later generations to ensure continued selection pressure for early physiological maturity.