Genetic variances and relationship among traits of an early maturing maize population under drought-stress and low nitrogen environments

Article purchasedDrought and low soil nitrogen (low N) are major causes of low grain yield of maize (Zea mays L.) in sub-Saharan Africa (SSA). An early maturing maize population, TZE-Y Pop DT STR, had undergone four cycles of selection for drought tolerance, followed by four selection cycles for resistance to Striga hermonthica (Del.) Benth., which is normally conducted under low N (about 30 kg N ha-1). The objectives of this study were to estimate residual genetic variances, predict future gains from selection, and investigate inter-trait relationships in the population under drought-stress, low N and across research environments. North Carolina Design I was used to develop 250 full-sib progenies from the improved population, which were evaluated in three drought-stress and two low N environments in Nigeria, 2011 to 2013. Additive genetic variances were not significant for most traits under the research conditions. The predicted gains from selection for grain yield were 5.3, 8.5 and 7.5% cycle-1 under drought, low N, and across environments. These results suggested the absence of substantial genetic variability in the population to ensure progress from selection. Ears per plant (EPP), ear aspect (EASP), plant aspect (PASP), and stay green characteristic (STGR) were consistently identified as important secondary traits under both research conditions. We concluded that there is need to introgress new sources of favorable alleles for drought-stress and low N tolerance into the population for guaranteed progress from selection, using EPP, EASP, PASP, and STGR in combination with yield in a selection index under drought-stress and low N

Yield gains in extra-early maize cultivars of three breeding eras under multiple environments

Open Access JournalAvailability of extra-early maize cultivars has facilitated the expansion of maize production into savannas of West and Central Africa (WCA). Fifty-six extra-early maize cultivars of three breeding eras;1995 to 2000, 2001 to 2006, and 2007 to 2012 were evaluated for 2 yr under 24 multiple-stress and 28 non-stress environments in WCA. Objectives of the study were to determine genetic improvement in grain yield of cultivars developed during the breeding eras, and identify high-yielding and s multiple-stress and non-stress environments. Yield gains from era 1 to era 3 under multiple stresses was associated with increased days to anthesis, reduced stalk lodging, and improved husk cover. Cultivars 2004 TZEE-Y Pop STR C4, TZEE-W Pop STR QPM C0, and TZEE-W Pop STR BC2 C0 of era 2; and TZEE-W STR 107 BC1, TZEE-W Pop STR C5, and 2012 TZEE-Y DT STR C5 of era 3 were high-yielding and stable across multiple-stress environments while 98 Syn EE-W from era 1, FERKE TZEE-W STR, TZEE-W Pop STR C3, and TZEE-Y Pop STR QPM C0 from era 2, and TZEE-W Pop STR C5, 2009 TZEE-OR2 STR QPM, 2009 TZEE-W STR, TZEE-Y STR 106, and TZEE-W DT C0 STR C5 from era 3 were outstanding across non-stress environments and should be tested extensively and commercialized. Considerable improvement has been made in breeding for multiple-stress tolerant extra-early maize cultivars

Agronomic traits associated with genetic gains in maize yield during three breeding eras in West Africa

Studies on genetic gains in grain yield in maize (Zea mays L) is crucial to identify traits of potential value and the necessary modifications in breeding methodologies and strategies for increased progress in future breeding ef-forts. Fifty early-maturing maize cultivars developed during three breeding eras were evaluated for 2 yr in two field experiments involving 16 multiple stress (drought, Striga-infested, and low soil nitrogen) environments and 35 optimum environments to determine the changes in agronomic traits associated with the genetic gains in grain yield over three breeding eras. The average rate of increase in grain yield was 30 kg ha–1 yr-1 corresponding to 1.59% annual genetic gain across multiple stresses. Among the agronomic traits under stress, only ears per plant (0.32% year-1), ear aspect (-0.51% year-1), plant aspect (-0.24% year-1) and days to anthesis (0.11% year-1) changed significantly (P<0.05 or <0.01) during the three eras. The increase in grain yield from the first to the third generation cultivars across stress environments was associated with significant improvements in plant and ear aspects, increased ears per plant and stay green characteristic. Under optimal growing environments, the increase in grain yield from the first to the third generation cultivars was 1.24% per annum and the gain was associated with significant improvements in plant and ear heights, plant and ear aspects, husk cover, and increased ears per plant. The results indicated that substantial progress has been made in breeding for cultivars with combined tolerance/resistance to the three stresses during the past 22 years

Maize genetic improvement for enhanced productivity gains in West and Central Africa

During the past 45 years, the genetic improvement programs of IITA and its partners have made spectacular progress in developing high-yielding crop varieties that offered best-bet solutions to major production constraints, such as, cassava mosaic, maize streak, Striga, soybean rust, insect pests, and even drought. These have led to dramatic increases in the production of cassava, maize, soybean, cowpea, and yam in sub-Saharan Africa that have directly contributed to increases in food availability and indirectly to improvements in national economies. This section presents the status, progress, and achievements, and also outlines future work on crop improvement by genetic enhancement in IITA's six crops

Combining ability of extra‐early biofortified maize inbreds under Striga infestation and low soil nitrogen

Open Access Article; Published online: 06 May 2020Striga hermonthica (Del.) Benth parasitism, low soil N, and nutritional deficiencies of normal‐endosperm maize (Zea mays L.) threaten maize yield and exacerbate nutritional problems in sub‐Sahara Africa (SSA). This study was conducted (a) to evaluate genetic variation among extra‐early maturing maize hybrids with provitamin A and quality protein characteristics, (b) to investigate gene action governing the inheritance of Striga resistance, grain yield, low N tolerance, and other measured traits under low‐N, high‐N, and Striga‐infested environments, and (c) to identify hybrids with high yield and stability across environments. One hundred and fifty hybrids developed using North Carolina Design II were evaluated with six checks under low‐N, high‐N, and Striga‐infested environments in Nigeria. Mean squares for hybrids were highly significant (P < .01) for grain yield and other traits across environments. Only general combining ability (GCA) for female and/or male mean squares were significant for measured traits under low N. In addition to significant GCA effects for most traits, specific combining ability was significant (P < .05) for Striga emergence count under Striga infestation, and ear height and ears per plant under high N, indicating that additive and nonadditive genetic effects controlled the inheritance of few traits under Striga and high N, whereas additive genetic effect governed the inheritance of the traits under low N. Hybrids TZEEIORQ 55 × TZEEIORQ 26, TZEEIORQ 49 × TZEEIORQ 75, and TZEEIORQ 52 × TZEEIORQ 43 were high yielding and stable across environments and have potential for improving nutrition and maize yields in SSA

Assessment of interrelationships among grain yield and secondary traits of early-maturing maize inbred lines under drought and well-watered conditions

Knowledge and understanding of interrelationships between grain yield and yield-related traits would ensure progress from selection in maize breeding programs through the use of appropriate selection indices. One hundred and fifty-sixearly-maturing maize inbreds were evaluated at fiveenvironments in Nigeria, for 2 years to assess the relationship between grain yield and yield-related traits of maize inbreds under drought and well-watered conditions. Genotypes, and genotype × environment interaction mean squares were significant(P<0.05) for grain yield and other measured traits under drought and well-watered conditions. Under drought, plant and ear aspects, ear height, ears per plant (EPP), leaf senescence, number of seeds per ear, and seeds per row had direct effects on grain yield, accounting for 76% of total variation. Under well-watered conditions, days to silking, ear aspect, ear height, EPP, ear length, 100-kernel weight, number of seeds per row, plant height, and stalk lodging had significantdirect effects on yield. Genotype main effect plus genotype × environment interaction (GGE) biplot identifiedplant and ear aspects, days to anthesis and silking, ASI, EPP, stay green characteristic, plant and ear heights, ear diameter, number of seeds per ear, number of seeds per row, and ear length as the most reliable traits for indirect selection for grain yield improvement under both research conditions. Plant and ear aspects, ear height, stay green characteristic, number of seeds per ear, and number of seeds per row were identifiedby both path–coefficientand GGE biplot analyses as the most reliable traits for selecting for grain yield under drought. Ear aspect, EPP, days to silking, plant and ear heights, number of seeds per row, and ear length were the most reliable traits for selecting for improved grain yield under well-watered conditions

Biplot Analysis of Line × Tester Data of Maize (Zea mays L.) Inbred Lines under Stress and Nonstress Environments

The GGE biplot tool has potential for determining combining ability effects, identifying distinct heterotic groups and efficient testers in a line × tester study. However, its use for such analysis has not been adequately explored. The objectives of this study were to (i) assess combining ability of extra-early maturing lines (80–85 days to physiological maturity) and testers for grain yield (ii) classify lines into heterotic groups and (iii) identify most efficient testers using GGE biplot. Sixty-three lines crossed to four testers were evaluated under Strga-infested, drought and nonstress environments for 2 years in Nigeria. Results of GGE biplot analyses of combining ability and heterotic patterns of yield of lines, grouping and identification of testers were close to those of the conventional line × tester method. Testers TZEEI 13, TZEEI 21 and TZEEI 29 were highly efficient in grouping lines under stress environments while testers TZEEI 21 and TZEEI 29 were best under nonstress environments. The GGE biplot identified tester TZEEI 13, TZEEI 21 and TZEEI 29 as most efficient across stress environments and TZEEI 21 and TZEEI 29 across nonstress environments