B. Badu-Apraku

Agronomic performance of maize cultivars representing three decades of breeding in the Guinea Savannas of West and Central Africa

Maize improvement at the International Institute of Tropical Agriculture (IITA), which began in the 1970s, built on the germplasm and experience of earlier years. The main breeding emphasis was to develop maize cultivars and hybrids with high yield potential and durable resistance to diseases and pests with specific adaptation to the different agro-ecological zones of West and Central Africa. Over the years, open-pollinated cultivars have been developed with different levels of resistance to biotic and abiotic stresses. Identification of the factors that contributed to improvements in the maize cultivars developed during the past decades may be useful to sustain the genetic gain from selection in the future. A study was conducted to quantify genetic gains in yield and associated traits of open pollinated maize cultivars released from 1970 to 1999 in the West African savannas. The genetic gain in grain yield was 0.41 % per year and seems to be associated with increases in total biomass and kernel weight, and reductions in plant height and days to flowering (anthesis and silking). There was no significant change in harvest index of the cultivars.

Genetic diversity assessment of extra-early maturing yellow maize inbreds and hybrid performance in Striga -infested and Striga -free 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 F 1 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 F 1 hybrids. However, a significant correlation existed between F 1 hybrid grain yield and heterosis under Striga infestation ( r =0·72, P Striga endemic areas in WCA.

Genetic Variability for Grain Yield and Its Components in an Early Tropical Yellow Maize Population Under Striga hermonthica Infestation

Abstract A major problem that usually confronts the breeder is ensuring that there is sufficient genetic variability in a population for the trait being improved because this determines the breeding schemes to use for improvement and whether or not sufficient progress could be made. Three hundred full-sib families from cycle 3 of the early maturing yellow endosperm maize (Zea mays L.) population, TZE-Y Pop DT STR, were evaluated under artificial Striga hermonthica infestation at Mokwa and Abuja, Nigeria in 2003. The objectives of this study were to investigate the type of gene action involved in the inheritance of S. hermonthica resistance in TZE-Y Pop DT STR C3, determine the extent of genetic variability available in the population after three cycles of S1 recurrent selection, and the phenotypic and genetic correlation coefficients among the traits used for selecting for resistance to S. hermonthica. Estimates of dominance variances were larger than additive genetic variances for grain yield, plant height, ear height, number of ears at harvest, and Striga damage rating at 8 weeks after planting (WAP). Even though h2 estimates were generally low for most traits (< 0.40), moderate-to-large additive genetic variances, and wide ranges were obtained in TZE-Y Pop DT STR C3 for most traits, suggesting that there was adequate genetic variation for improving Striga resistance and grain yield in the population. Highly significant phenotypic correlation coefficients were obtained between grain yield and ears per plant, plant height, ear height, days to anthesis and silking, anthesissilking interval, and Striga damage score at 10 WAP. Recurrent selection methods that capitalize on both additive and dominance variances would be effective for improving the population for Striga resistance and grain yield.

Estimates of Genetic Variances in Striga Resistant Extra-Early-Maturing Maize Populations

Abstract Breeders should maintain sufficient genetic variability in a population to ensure continuous advance from selection for a target trait. The extra-early-maturing Striga resistant/tolerant maize (Zea mays L.) populations, TZEE-W Pop DT STR (white) and TZEE-Y STR (yellow), have each gone through three cycles of S1 recurrent selection for improvement for grain yield, Striga resistance under artificial Striga infestation, and other desirable agronomic characters. S1 families derived from cycle 3 of each population were evaluated at Mokwa and Abuja in Nigeria in 2003 under artificial Striga hermonthica infestation. The objectives of this study were to determine the genetic variability, herita-bilities, and genetic advance among traits associated with Striga resistance in each population. Results showed that the estimates of genetic variance, a 2 were moderate to large for most traits of TZEE-W Pop STR C3 with the exception of husk cover and Striga emergence count at 8 and 10 weeks after planting (WAP). Out of 13 traits of TZEE-Y Pop STR C3, 7 had moderate-to-large genetic variances whereas the others were much lower. Broad-sense heritability estimates of traits in TZEE-Y Pop STR C3 were moderate-to-large for days to silking and anthesis; other traits had generally low heritabilities (<0.50). On the other hand, heritability estimates in TZEE-W Pop STR C3 were moderate-to-large for days to anthesis and plant height, and generally low for the other traits. The percentage predicted gain from selection for the traits of TZEE-Y Pop STR C3 ranged from 2.82 for Striga damage rating at 8 WAP to 22 for grain yield; the percentage gain for grain yield of TZEE-W Pop STR C3 was 25 and 0.37–39.21 for 12 other traits. Highly significant positive or negative phenotypic correlations were detected between grain yield and most other traits for TZEE-W Pop STR C3. The correlations between grain yield and other traits of TZEE-Y Pop STR C3 followed trends similar to those of TZEE-W Pop STR C3. The results suggest that sufficient residual genetic variability still exists in each population to allow good progress from further selection for grain yield and Striga resistance.

Genetic gains in grain yield under nitrogen stress following three decades of breeding for drought tolerance and Striga resistance in early maturing maize

Breeding for resistance to Striga hermonthica Del. (Benth) and tolerance to drought has been a major strategy to improve maize ( Zea mays L.) production and productivity in West and Central Africa during the last three decades. The three decades consisted of three breeding periods or eras based on the germplasm and methodologies used; that is, 1988–2000, 2001–06 and 2007–11. A total of 50 early maturing cultivars, combining Striga resistance with drought tolerance were developed, including 15, 16 and 19 cultivars for the three periods, respectively. Although the cultivars were not selected intentionally for low-nitrogen (N) tolerance, it was hypothesized that tolerance to low-N had been significantly improved while selecting for drought tolerance and Striga resistance. This hypothesis was tested by evaluating the 50 cultivars in 2010 and 2011 in Nigeria at Mokwa and Ile-Ife under both low-N (30 kg N/ha) and high-N (90 kg N/ha) levels. Under low-N conditions, grain yield improved from 2280 kg/ha during the first period to 2610 kg/ha during the third period, an increase of 165 kg/ha per period with r 2 of 0·99. Under high-N, yield increased from 3200 to 3650 kg/ha, an increase of 225 kg/ha and r 2 of 0·93. Relative gain per period was 30 kg/ha for the two N rates with r 2 values of 0·99 and 0·94 respectively. Grain yield performance of the 50 cultivars under low-N conditions adequately predicted their performance under high-N. Selection for Striga resistance and drought tolerance in early maturing maize populations enhanced low-N tolerance in the maize cultivars derived from the populations. The improvement was higher in later than earlier breeding periods.

Introgression of Alleles from Maize Landraces to Improve Drought Tolerance in an Adapted Germplasm

Maize (Zea mays L.) landraces in the northern Guinea savanna and Sudan savanna in West and Central Africa appear to have some drought-adaptive traits. This study was initiated to assess the level of improvement in yield potential and other agronomic traits achieved under drought stress (DS) and in multiple locations (ML) after introgression of alleles from maize landraces into an elite maize variety (AK9443-DMRSR) via backcrossing. Six backcross (BC) populations together with recurrent parent (AK9443-DMRSR), a commercial hybrid (Oba Super-II), and an improved variety (TZLCOMP4C1) were evaluated under controlled DS and full irrigation (FI) during the dry seasons of 1999 and 2000, as well as in seven ML trials. No significant differences were observed among genotypes for grain yield and most of the traits measured under DS and FI. Significant differences were recorded among genotypes for grain yield and other agronomic traits measured in ML and across 11 environments. Drought stress reduced grain yields of the BC1F2 populations by 64% and recurrent parent by 71%. In ML trials, at least half of the populations were better than recurrent parent. The top three BC1F2 populations produced more grains than the recurrent parent (258–360 kg/ha) and Oba Super-II (555–657 kg/ha) with introgression of only 25% genome of the landraces. We concluded that backcross procedure was able to transfer a quantitative trait of grain yield of an elite recurrent parent into maize landraces. Additional backcross generations are needed for improved performance of the BC1F2 populations in drought-prone environments.

Enhancing the capacity of national scientists to generate and transfer maize technology in west and central Africa : Research implementation, monitoring and evaluation

The West and Central Africa Collaborative Maize Research Network (WECAMAN) was established in 1987 to strengthen the capacity and capability of national programmes of West and Central Africa (WCA) to tackle regional constraints to maize production. The Network created several mechanisms for implemenling, monitoring and evaluating maize research and development activities, including research project development and implementation, attendance and quality of paper presentation at techanical conferences organized by the Network, scientific monitoring tours, consultation visits, mid-term reviews, and end-of-project reviews and impact assessment. WECAMANs approach to the system of allocating research responsibilities and competitive grants resulted in increased research efficiency and the generation of sustainable technologies that have catalysed increased maize production in the region.

Maize in Sub-Saharan Africa: Importance and Production Constraints

Maize (Zea mays L.), an important food, feed, and industrial crop in sub-Saharan Africa (SSA), has been researched extensively for genetic enhancement for more than a half century in the subregion. One aspect that received intensified research attention in the last three or four decades is the genetic enhancement of early and extra-early maturing germplasm for resistance or tolerance to drought, Striga, and low soil nitrogen. Improved open-pollinated varieties (OPVs) and hybrids with tolerance/resistance to the stresses and/or high levels of micronutrients such as beta carotene along with elevated levels of lysine and tryptophan are now available in SSA. A brief description of the achievements and the challenges still confronting maize breeders and geneticists is presented in this chapter.

Genetic analysis of drought-adaptive traits at seedling stage in early-maturing maize inbred lines and field performance under stress conditions

Maize hybrids that are tolerant to drought at the seedling stage are needed to boost productivity in the rainforest agro-ecology of West Africa. Genetics of tolerance of maize seedling to drought stress is not well understood and is poorly documented. The objectives of this study were to screen early-maturing maize lines for seedling drought tolerance, determine the inheritance and the combining ability of selected inbred lines, and evaluate the performance of seedling drought-tolerant hybrids under field conditions. Forty-nine early maize lines were screened for drought tolerance at the seedling stage. Ten drought-tolerant and two susceptible inbred lines were selected and used in diallel crosses to generate 66 hybrids. The twelve inbred lines and their hybrids were evaluated under induced drought at seedling stage in the screen house and under marginal growing conditions on the field for two seasons. Data collected were subjected to analysis of variance using the DIALLEL-SAS program. Mean squares for both GCA and SCA were significant for most traits in all research environments, indicating that additive and non-additive gene actions are controlling seedling traits under stress conditions. However, for most traits, SCA was preponderant over GCA in all environments, indicating overdominating effect of non-additive gene action. Which in turn implied that the best improvement method for the traits is hybridization. Inbred TZEI 7 had the best GCA effect for seedling traits under screenhouse conditions and for grain yield and other agronomic traits under drought conditions in the field. Hybrids TZEI 357 × TZEI 411 and TZEI 380 × TZEI 410 showed superior SCA effects under screen house conditions. In conclusion, the study established wide genetic variability for drought tolerance at seedling stage among tropical early-maturing maize germplasm however, the non-additive gene action was more important for most seedling traits.

Gains in Grain Yield of Extra-Early Maize during Three Breeding Periods under Drought and Rainfed Conditions

Drought is a key maize (Zea mays L.) production constraint in sub-Saharan Africa. Fourteen, fifteen, and twenty-five extra-early maturing maize cultivars, with varying Striga resistance and drought and low soil N tolerance, were developed from 1995 to 2000 (Period 1), 2001 to 2006 (Period 2), and 2007 to 2012 (Period 3), respectively. The objectives of this study were to examine yield gains in the cultivars and to investigate inter-trait relationships and yield stability under six drought and 17 rainfed conditions in West Africa from 2013 to 2016. Annual rate of yield increase across cultivars was 0.034 (3.28%) and 0.068 Mg ha−1 (2.25%), whereas yield gains per period were 0.17 and 0.38 Mg ha−1 under drought and rainfed environments, respectively. Yield gains under drought and rainfed environments were related to prolonged flowering period, increased plant and ear heights, improved stalk lodging, and ear and plant aspects, whereas delayed leaf senescence and increased number of ears per plant accompanied yield improvement under drought only. Ear aspect and number of ears per plant were primary contributors to yield and could be used as selection criteria for yield enhancement under drought and rainfed conditions. High-yielding and stable cultivars across all environments based on additive main effects and multiplicative interaction (AMMI) biplot included ‘2004 TZEE-Y Pop STR C4’ and ‘TZEE-W Pop STR BC2 C0’ of Period 2 and ‘2009 TZEE-W STR’, ‘TZEE-Y STR 106’, ‘TZEE-W STR 107’, and ‘TZEE-W DT C0 STR C5’ of Period 3. These cultivars could be commercialized to improve food self-sufficiency in sub-Saharan Africa.