Genotype × environment interactions complicate selection of superior genotypes for narrow and wide adaptation. Eighteen tropically-adapted maize cultivars were evaluated at six locations in Nigeria for 2 yrs to (i) identify superior and stable cultivars across environments and (ii) assess relationships among test environments. Environment and genotype × environment interactions (GEI) were significant (P < 0·05) for grain yield. Environments accounted for 63.5% of the total variation in the sum of squares for grain yield, whereas the genotype accounted for 3.5% and GEI for 32.8%. Grain yield of the cultivars ranged from 2292 kg ha -1 for DTSTR-W SYN2 to 2892 kg ha -1 for TZL COMP4 C3 DT C2 with an average of 2555 kg ha -1 . Cultivar DT SYN2-Y had the least additive main effect and multiplicative interaction (AMMI) stability value of 7.4 and hence the most stable but low-yielding across environments. AMMI biplot explained 90.5% and classified cultivars and environments into four groups each. IWD C3 SYN F3 was identified as the high-yielding and stable cultivar across environments. ZA15, ZA14, BK14, BK15 and IL15 had environment mean above the grand mean, while BG14, BG15, LE14, LE15, IL14, LA14 and LA15 had mean below the grand mean. ZA, BK, BG, LE and LA were found to be consistent in ranking the maize cultivars. However, Zaria, Birnin Kudu, and Ilorin were identified as the best test locations and could be used for selecting the superior maize cultivars. The identified high-yielding and stable cultivar could be further tested and promoted for adoption to contribute to food insecurity in Nigeria.

Maize (Zea mays L.) grain yield is severely constrained by drought and this study was conducted to assess gains in grain yield and other traits of released maize cultivars. Twenty-three maize cultivars plus a check were evaluated under drought and well-watered conditions at Zaria and Kadawa during 2015/2016 and 2016/2017 dry seasons. The 24 cultivars were evaluated using 6 x 4 lattice design with three replications. Genotypes differed significantly for all measured traits except anthesis-silking interval (ASI), husk cover, and number of ears per plant under drought, and ASI, husk cover, and ear aspect under well-watered conditions. Under drought, grain yield ranged from 2251 kg ha−1 for SAMMAZ 31 to 4938 kg ha−1 for SAMMAZ 19, with a genetic gain of 1.93% yr−1. Under well-watered conditions, grain yield varied from 3082 kg ha−1 for SAMMAZ 37 to 5689 kg ha−1 for SAMMAZ 51, with the same genetic gain found under drought conditions. Grain yield reduction as a result of drought was 28.4% and performance under drought predicted performance under well-watered conditions better than vice versa with regression coefficient value of 0.8. Grain yield had significant correlations with all measured traits under both water conditions, except for husk cover, plant and ear heights under drought. Our data revealed that substantial genetic gains have been made in breeding for high grain yield cultivars under drought and well-watered conditions over a period of 16 years in Nigeria.

Colchicine at various concentration was given to the apical buds of maize (Zea mays L.). Plants, in order to induce tetraploidy for meiotic studies. Highly irregular meiosis in the C 1 generation was revealed. These meiotic abnormalities increased pollen sterility which lead to a lower seed setting. In the C 2 generation the occurrence of bivalents has increased and that of multivalents has decreased. Restoration of meiotic regularities, pollen fertility.

In this study, an optimum protocol for shoot formation through somatic embryogenesis using mature embryo explants was developed. Calli were initiated on Murashige and Skoog (MS) media supplemented with varying concentration of 2,4-Dichlorophenoxyl acetic acid (2,4-D) ranging from 1.5 mg/l-4.0 mg/l alone or in combination with 0.5 mg/l Kinetin (KN). Significance difference (p < 0.05) was observed among the different concentrations of hormone used for callus induction. The highest percentage callus formation was obtained from the media fortified with 4 mg/l 2, 4-D for mature embryo obtained from imbibed seed while for the preconditioned mature embryo, the media supplemented with 2 m/l 2,4-D + 0.5 mg/l kinetin (KN) recorded more percentage callus formation compared to what was obtained from the media supplemented with 2.5 mg/l2,4-D + 0.5 mg/l. More percentage shoot formation was obtained from the media supplemented with 1 mg/l 6-benzylaminopurine (BA). Average number of shoot per callus was also more in the media fortified with 1 mg/l BA (2.25) but this was not significantly different from what was obtained from the media fortified with 2 mg/l BA+ 0.1 mg/l 2,4-D at 5% level of significance.

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