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The cowpea aphid (Aphis cracivora) is a cosmopolitan insect pest that causes economic damage on cowpea. Although the pest persists at all the growth stages of the crop, in West Africa, aphids are the only major insect pests that farmers regularly control at the vegetative stage. Thus, deploying aphid-resistant crop varieties can reduce farmers' expenditure on insecticide. The availability of different biotypes of the pest and reports of resistance breakdown necessitates pyramiding of sources of aphid resistance to develop a more robust genotype for durable resistance. Two aphid-resistance genes, sourced from SARC-1-57-2 and IT97K-556-6, were introgressed through gene pyramiding technique into a farmers’ preferred cowpea variety, Zaayura, using marker-assisted backcrossing. A simple sequence repeat (SSR) marker, CP 171F/172R, and an allele-specific single nucleotide polymorphism (SNP) marker, 1_0912, were used for foreground selection of the SARC-1-57-2 and IT97K-556-6 aphid resistance genes, respectively. A stepwise backcross approach was used to introgress the major aphid resistance QTL (QAc-vu7.1) from IT97K-556-6 into Zaayura using the marker 1_0912 coupled with intermittent screening under artificial aphid infestation. After the fourth backcross generation, three heterozygous BC4F1 of Zaayura/TT97K-556-6 were intercrossed to Zaayura Pali to develop intercross F1 (ICF1). Three true ICF1 hybrids allowed to self to produce ICF2. Five (5) out of 48 ICF2 plants which were genotyped with the two foreground markers had the two aphid resistance genes fixed in the double homozygous dominant state. For background selection, out of 192 allele-specific markers screened, only 47 polymorphic markers were identified and used for the background analysis of the pyramided lines. The recurrent parent genome recovery ranged from 72 to 93.8 %. ICF2_Zaa/556/SARC-P6 had the highest recurrent parent genome and the least heterozygosity among the five improved lines. The five pyramided lines showed superior resistance under artificial aphid infestation as compared to the two donor parents with damage scores ranging from 2.0 to 2.3. On the field, however, there were no significant differences between the pyramided lines and their recurrent parent for all the agronomic traits measured except for grain yield. The pyramided lines do not only stand the chance of being released as new varieties but are also valuable genetic resources for other breeding programs that seek to improve cowpea for aphid resistance.

The potential of cowpea (Vigna unguiculata [L] Walp) to contribute to food security and livelihood sustenance of sub-Sahara Africans is constantly threatened by many biotic and abiotic stresses that are aggravated by climate change. To address these threats, cowpea breeding programs in the subregion prioritize climate-resilience traits and resistance to biotic stresses. However, before successful trait discovery and implementation, it is essential to characterize diversity and population structure of cowpea germplasm. To test the hypothesis that assembled cowpea germplasm exhibits limited and narrow genetic diversity with a well-defined population structure, we assessed the level of genetic variability and characterized the population structure of 188 cowpea genotypes using 5147 Single Nucleotide Polymorphism (SNP) markers. The structure results revealed five major genetic groups with moderate levels of genetic diversity and an admixture level of 17 %. Discriminant analysis and phylogenetic analysis supported this finding, indicating the presence of distinct groups within the cowpea population. The analysis of molecular variance (AMOVA) showed 27 % among population variance, 64 % within-population variance, and 9 % within individual variance. While considering the origin, the AMOVA showed 16 % among population variance, 75 % among individual variance, and 9 % within individual variance. This study provides valuable insights for future cowpea improvement programs by facilitating the selection of suitable progenitors for population development, and contributing in the conservation of cowpea genetic resources. Addressing these challenges and enhancing cowpea's diversity and resilience are crucial steps towards ensuring food security and sustainable livelihoods in sub-Saharan Africa.

Maize yield losses due to fall armyworm (FAW) infestation is in the range of 22–67%, amounting to millions of US dollars in sub-Saharan Africa (SSA). Identifying new sources of maize genotypes with resistance to insects and a better understanding of resistance mechanisms have opened the avenue for the exploration of host-plant resistance (HPR). The present study was carried out to assess the resistance of maize inbred lines and hybrids to FAW foliar feeding damage through natural and artificial screening. Thirty-five (35) maize inbred lines obtained from the International Maize and Wheat Improvement center (CIMMYT) and the United State Department of Agriculture – Agricultural Research Services (USDA–ARS) were screened for fall armyworm resistance in Ghana in 2019. In addition, sixty (60) single-cross hybrids and twenty (20) double-crosses developed from 17 desirable inbred lines were evaluated for resistance to fall armyworm using artificial and natural infestations in 2020 and 2021. Significant differences were recorded among the inbred lines, F1 hybrids, and the double-crosses. The cluster and principal component analysis classified the thirty-five inbred lines into four groups suggesting the presence of wide variability. Hybrids (CML343*CML 346)//(CML124*MP 713), (MP713*MP705)//(CML123*MP713), (CML331*MP701)//(MP702*MP705), (CML330*MP702)//(CML123*MP706), (CML122*MP713)//(CML330*MP701), (OBT*MP708)//(MP713*MP705),MP704*CML122)//(CML123*MP713), (CML123*MP708)//(CML122*MP713) and (CML330*MP701)//(MP713*MP705) were found to be promising. These hybrids should be recommended for further testing and commercialization in SSA.

The nature of gene action controlling agronomic traits enables plant breeders to execute a successful crop improvement programme. To elucidate the type of gene action governing the key earliness related traits in cowpea, seven populations of the six basic generations, viz; P1, P2, F1, F2, BC1 and BC2 were developed by crossing three extra-early and three early-to-medium maturing parental lines. Each of the populations were sowed in Randomised Complete Block Design, in the experimental field of Council for Scientific and Industrial Research (CSIR)-Savana Agricultural Research Institute Manga, Ghana. Observations were made on days to first flower appearance (DFFA) and days to 95% pod maturity (DNPM). The results indicated that the epistatic gene interaction for DFFA in most of the crosses was duplicate epistasis between dominant decreasers. For DNPM, duplicate epistasis between dominant increasers was found. Only Kirkhouse-Benga × CB27 revealed complementary epistasis between dominant decreasers for both traits. Among the significant epistasis terms re-estimated using perfect fit procedure, the χ2 values were not applicable in any of the crosses, indicating the inadequacy of the six-parameter model of digenic epistasis. Therefore, trigenic or other high-order epistasis could be responsible for the inheritance of the traits evaluated. This implies that improvement of earliness in cowpea could be achieved through hybridization method, followed by selection of promising recombinants in later generation, for crosses governed by duplicate epistasis. Complementary epistasis detected for one of the crosses is desirable and would be beneficial in the development of early duration varieties, where selection could be done at early generation. The preponderance of partial-dominance, over-dominance of earliness over late maturity, and significant negative heterosis and heterobeltiosis observed for DFFA and DNPM indicated that the developed of short duration cowpea cultivars would be efficient. The genetics of the three most popular extra-early maturing cowpea genotypes reported in this study could be exploited by breeders to develop extra-early duration varieties.

Global climate change is expected to further intensify the already harsh conditions in the dry savannah ecological zones of sub-Saharan Africa, posing serious threats to food and income security of millions of smallholder farmers. Breeding cowpea for improved earliness could help minimize this risk, by ensuring that the crops complete their lifecycle before the cessation of rainfall. In this study, we crossed two sets of cowpea lines showing contrasting phenotypes for earliness in terms of days to 50% flowering (DFF). One set of the lines comprised three extra-early parents (viz.: Sanzi-Nya, Tobonaa and CB27, 30–35 DFF), and the other set consisted of three early-to-medium maturity lines (viz.: Kirkhouse-Benga, Wang-Kae and Padi-Tuya, 42–45 DFF). The derived crosses and their parents were evaluated for key earliness-related traits at Nyankpala and Manga sites of CSIR-Savanna Agricultural Research Institute (SARI), Ghana. To unravel the genetic control of measured traits, we compared the appropriateness of Chi-square goodness of fit tests using classical Mendelian ratios, and frequency distribution (histogram)-related statistics such as skewness and kurtosis. The Chi-square test suggested a single dominant gene mode of inheritance for earliness, whereas the quantitative methods implicated duplicate epistasis and complementary epistatic gene actions. Our results show that coercing segregating lines to fit into classical Mendelian ratios to determine the genetic control of earliness could be misleading, due to its subjectivity. Thus, the genetic control of earliness in cowpea is governed by complementary and duplicate epistasis. The most applicable breeding approach for traits influenced by duplicate epitasis is selection of desirable recombinants from segregating populations developed from bi-parental crosses. Complementary epitasis, as found in the Wang-Kae × CB27 cross, could be exploited in developing improved extra-early lines through backcrossing. Heritability and genetic advance estimates were high for days to first flower appearance (DFFA) and days to 95 % pod maturity (DNPM) in the Padi-Tuya × CB27 and Kirkhouse-Benga x CB27 crosses, indicating that breeding for extra-earliness is feasible. CB27 could be a good donor for introgression of earliness into medium to late maturing improved cowpea varieties, because crosses developed from it had high heritability and genetic advance estimates.

Anther indehiscence in certain wide crosses combines male sterility with stigma exertion, a phenomenon that is desirable for hybrid rice seed production. This study sought to identify chromosomal region(s) that combine anther indehiscence with exerted stigmas. A mapping population consisting of 189 BC1F1 plants was derived from a cross between CRI-48 and Jasmine 85 and backcrossing the resulting F1 to Jasmine 85. Contrary to the three complementary genes mode of inheritance reported earlier, a single locus (AI6-1) was mapped on chromosome 6 at 27.4 cM for anther indehiscence with exerted stigmas through a mixed model-based composite interval mapping (MCIM). This locus was flanked by two single nucleotide polymorphism (SNP) markers, K_ID6002884 and K_ID6003341 within a range of 23.1–28.9 cM. The allele at the locus was contributed by the CRI-48 parent which has Oryza glaberrima ancestry. This locus is suggested to control anther indehiscence and stigma exertion through pleiotropic gene action or cluster of genes.