Relationship between line per se and cross performance under low nitrogen fertility in tropical maize (Zea mays L.)

Abstract

Improved maize yields under low nitrogen (N) fertility is desired for both low- input production systems and also for judicious application of fertilizer nitrogen for a sustainable and environment friendly production systems. A key question in breeding for tolerance to low-N fertility is to what extent the performance of maize hybrids can be predicted on the basis of performance of their inbred lines under low-N supply. Past studies showed varied degree of correlations between line and hybrid performance under low-N fertility, ranging from weak to fairly strong relationship. We attempted to examine the impact of low-N supply on relationship between morpho-physiological traits and grain yield measured on inbred parents, all advance generation lines, and their single cross progenies. Reactions of various morpho-physiological traits, except days to anthesis (male flowering), differ significantly at low- and optimal level of N-fertility. Superiority of hybrid progenies over parental lines declined under low-N stress, which indicates that hybrids were comparatively more affected than lines due to low-N supply. Data on individual contributions of heterosis and performance of mid-parent showed that per se performance of lines was relatively more important factor in determining the hybrid performance under both the levels of N-supply. Correlations between various secondary traits and grain yield under both low and optimal-N fertility were moderate to strong in case of both parental lines and hybrids. However, it was comparatively stronger in case of hybrid progenies under low-N stress. Correlations between morpho-physiological traits of lines and hybrids, except for ear rots, were fairly strong and significant under both the level of N supply. The relationship between grain yield of mid-parent and hybrids was comparatively stronger under low-N fertility. Our findings suggest that performance of hybrid progenies under low-N fertility can be predicted to some extent on the basis of advance generation elite inbred parents with proven performance across N-supply.