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

EVALUATION OF STRIGA-RESISTANT EARLY MAIZE HYBRIDS AND TEST LOCATIONS UNDER STRIGA-INFESTED AND STRIGA-FREE ENVIRONMENTS

Emergence of several seed companies in the West Africa sub-region during the last decade has necessitated intensified efforts towards hybrid development and extensive testing. The objectives of the present study were to evaluate selected Striga-resistant maize ( Zea mays L.) hybrids for grain yield and stability of performance based on multiple traits. Thirty Striga-resistant single\u2013cross maize hybrids plus two checks were evaluated under artificial Striga infestation and Striga-free conditions at 2 locations in Nigeria in 2008 and 2009. The two test locations possessed high discriminating ability. More promising genotypes were identified under Striga infestation based on multiple traits than based on yield per se, suggesting that grain yield alone is not a precise predictor of Striga resistance. Based on both biplot analyses, TZEI12 x TZEI25 was identified as the most outstanding in performance under both research conditions. Furthermore, TZEI11 x TZEI127 and TZEI80 x TZEI2B were identified as the most outstanding under Striga-infested conditions and TZEI60 x TZEI87 under Striga-free conditions by the two biplot methods. The hybrids with outstanding performance should undergo extensive multilocational testing and promotion for adoption for commercial production.L\u2019\ue9mergence de plusieurs companies de semence dans la sous r\ue9gion weste africaine durant la derni\ue8re decades a n\ue9cessit\ue9 des efforts intensifi\ue9s en d\ue9veloppement d\u2019hybrides et essais extensifs. Les objectifs de la pr\ue9sente \ue9tude \ue9taient d\u2019\ue9valuer des hybrides s\ue9lectionn\ue9s de ma\uefs ( Zea mays L.) r\ue9sistants au striga pour le rendement en grains et la stabilit\ue9 de sa performance sur base de multiples traits. Trente hybrides de ma\uefs r\ue9sistants \ue0 un seul croisement ainsi que deux t\ue9moins \ue9taitent \ue9valu\ue9s en condition artificielle d\u2019infestation et dans des conditions sans Striga dans deux milieux du Nigeria en 2008 and 2009. Les deux milieux en tests possedaient une aptitude discriminatoire \ue9lev\ue9e. Plus de g\ue9notypes promettants \ue9taient identifi\ue9s en condition d\u2019infestation du Striga, en se basant sur des traits multiples plut\uf4t que sur base du rendement, sugg\ue9rant que seul le rendement en grain n\u2019est pas un pr\ue9dicteur pr\ue9cis de la r\ue9sistance du striga. Bas\ue9 sur les analyses biplot, TZEI12 x TZEI25 \ue9tait identifi\ue9 comme le plus remarquable en performance sous conditions de recherche. En plus, TZEI11 x TZEI127 et TZEI80 x TZEI2B \ue9taient identifies comme \ue9tant les plus remarquables en conditions d\u2019infestation du Striga et TZEI60 x TZEI87 sous conditions non infest\ue9es du Striga par deux methods biplot. Des \ue9tudes extensives multilocales des hybrides \ue0 performance remarquable ainsi que la promotion de l\u2019adoption pour une production commerciale sont recommend\ue9es

Testcross performance and combining ability of early maturing maize inbreds under multiple-stress environments

Open Access Journal; Published online: 24 Sept 2019Availability of multiple-stress tolerant maize is critical for improvement in maize production in West and Central Africa (WCA). A study was carried out to (i) assess a set of inbred lines for combining ability under stressed and optimal conditions, (ii) determine the performance of the testcrosses under different conditions, and (iii) identify outstanding hybrids across the conditions. Two hundred and five testcrosses were planted with five hybrid checks under Striga-infested, low soil nitrogen, drought and optimal conditions between 2015 and 2016 in Nigeria. The grain yield inheritance under optimal condition was largely regulated by additive gene effect whereas non-additive gene effects largely regulated grain yield under the three stresses. Four of the inbreds had significant positive general combining ability effects each under low N and drought, and three under Striga infestation for grain yield. The inbreds could be vital sources of beneficial alleles for development and improvement of tropical yellow maize hybrids and populations. Hybrids TZEI 443 x ENT 13 and TZEI 462 x TZEI 10 were high yielding and stable; they out-performed the three early maturing released hybrids in WCA. The new hybrids should be extensively assessed and released in the sub-region to improve food security

Identification of early and extra-early maturing tropical maize inbred lines resistant to Exserohilum turcicum in sub-Saharan Africa

Open Access Article; Published online: 12 Sept 2020Northern corn leaf blight (NCLB) incited by the fungus Exserohilum turcicum is a foliar disease that significantly limits maize production and productivity in West and Central Africa (WCA), particularly in the mid-altitudes but during the last decade it has become a menace in lowland agro-ecologies. The most economical and environmentally friendly disease management strategy is the cultivation of maize varieties resistant or tolerant to NCLB. However, no early maturing (EM) and extra-early maturing (EEM) NCLB resistant varieties are commercially available in WCA. One hundred inbred lines each of EM and EEM derived from tropical maize germplasm were inoculated with a virulent isolate of E. turcicum at five locations in Nigeria during the 2017 and 2018 growing seasons. The objective of the study was to identify promising NCLB resistant lines and to investigate inter-relationships among the traits. Analysis of variance revealed highly significant genotype and genotype by environment (G × E) interactions for disease severity, grain yield (GYLD), and other agronomic traits. The average disease severity (TURC) values ranged from 1.9 to 5.8 and 2.9 to 5.7 for the EM and EEM inbred lines, respectively. The levels of reaction of the inbred lines to NCLB ranged from highly resistant to highly susceptible. Stepwise regression analysis showed that ears per plant, ear and plant aspects were significantly influenced by the disease scores. Ears per plant, ear and plant aspects, TURC and GYLD traits were employed to develop a base index (BI) for selecting NCLB resistant inbred lines for hybrid development. TZEI 135 and TZEEI 1 were outstanding in GYLD and also had the highest positive BI values in the EM and EEM inbred lines, respectively. The identification of NCLB resistant lines in this study has set the premise for development of NCLB resistant hybrids for WCA as well as the improvement of tropical maize breeding populations for NCLB resistance