Genetic diversity assessment of extraearly maturing yellow maize inbreds and hybrid performance in Strigainfested and Strigafree environments

Maize (Zea mays L.), a major staple food crop in West and Central Africa (WCA), is adapted to all agro-ecologies in the sub-region. Its production in the sub-region is greatly constrained by infestation of Striga hermonthica (Del.) Benth. The performance and stability of the extra-early maturing hybrids, which are particularly adapted to areas with short growing seasons, were assessed under Striga-infested and Striga-free conditions. A total of 120 extra-early hybrids and an open-pollinated variety (OPV) 2008 Syn EE-Y DT STR used as a control were evaluated at two locations each under Striga-infested (Mokwa and Abuja) and Striga-free (Ikenne and Mokwa) conditions in 2010/11. The Striga-resistant hybrids were characterized by higher grain yield, shorter anthesis–silking interval (ASI), better ear aspect, higher numbers of ears per plant (EPP), lower Striga damage rating, and lower number of emerged Striga plants at 8 and 10 weeks after planting (WAP) compared with the susceptible inbreds. Under Striga infestation, mean grain yield ranged from 0·71 to 3·18 t/ha and 1·19 to 3·94 t/ha under Striga-free conditions. The highest yielding hybrid, TZEEI 83×TZEEI 79, out-yielded the OPV control by 157% under Striga infestation. The hybrids TZEEI 83×TZEEI 79 and TZEEI 67×TZEEI 63 were the highest yielding under both Striga-infested and Striga-free conditions. The genotype main effect plus genotype×environment interaction (GGE) biplot analysis identified TZEEI 88×TZEEI 79 and TZEEI 81×TZEEI 95 as the ideal hybrids across research environments. Twenty-three pairs of simple sequence repeat (SSR) markers were used to assess the genetic diversity among the inbred lines. The correlations between the SSR-based genetic distance (GD) estimates of parental lines and the means observed in F1 hybrid under Striga infestation and optimum growing conditions were not significant for grain yield and other traits except ASI under optimum conditions. Grain yield of inbreds was not significantly correlated with that of F1 hybrids. However, a significant correlation existed between F1 hybrid grain yield and heterosis under Striga infestation (r=0·72, P