Nitrate‐Reductase Activity and Grain Yield of Maize Cultivar Hybrids1

Abstract

Nitrate‐reductase activity (NRA) has been suggested as an indirect selection criterion for grain yield in maize (Zea mays L.). This assumes that because of linkage or pleiotropism selection for higher levels of one of these traits would result in a correlated positive response in the other. We tested this hypothesis with maize cultivar hybrids obtained from two recurrent selection programs for improved grain yield.Five maize cultivar hybrids [BSSS(R)CO ✕ BSCB1 (R)CO, BSSS(R)C5 ✕ BSCB1(R)C5, and BSSS(R)C7 ✕ BSCB1(R)C7 from a reciprocal recurrent selection program involving Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic #1 (BSCB1), and BS12CO ✕ B14A and BS12C6 ✕( B14A from a half‐sib family selection program with the open‐pollinated cultivar ‘Alph’ (BS12)] were grown in 1975 and 1976 at four levels of fertilizer N (0, 90, 180, and 270 kg N/ha) and two plant densities (39,500 and 98,800 plants/ha) in Experiment I. Also, CO )✕ CO and C7 ✕ C7 from the reciprocal recurrent selection program and the hybrids from the half‐sib program were grown in 1975 and 1976 at 59,300 and 98,800 plants/ha with 178 kg N/ha (Experiment II). We assayed NRA by the in vivo technique during the vegetative, anthesis, and grain‐filling stages of development.Our results showed that average NRA did not change with selection for increased grain yield in the reciprocal recurrent selection program, but selection for improved grain yield in BS12 (half‐sib selection program) was associated with decreased NRA.