No abstract

African yam bean (AYB, Sphenostylis stenocarpa Hochst. ex A. Rich.) Harms is a tuber and seed crop, rich in protein, with the potential to contribute to food security. To date, available information on the diversity of AYB is scarce. This study aims at understanding the genetic diversity of 79 AYB accessions of various origins. Twenty-four morphological and taxonomic features of high descriptive values were used and the diversity within the germplasm was assessed by clustering analysis. The 79 accessions differed significantly, with the similarity distances spanning from 0.0646 to 0.5720 and a mean distance of 0.2820. The accessions were grouped into five clusters of 10-26 members. Of the 24 phenotypic variables analyzed, variegation in testa color was the most discriminatory trait, classifying the accessions in the proportion of 25% with variegated to 75% with non-variegated seeds. The ranking by significance (P B 0.05) of the ordinal variables of discriminating importance were in the order of pattern of testa variegation, basal color of variegated seeds, and testa basal color. The stepwise discriminant and frequency procedures in SAS identified other phenotypic variables with significant discriminatory attributes, such as pigmentation of plant parts, seed cavity ridges, and pod dehiscence. Accessions with desirable agronomic traits, such as longer pod length, high number of seeds/pod, non-shattering characteristics of pods at maturity, lower number of days to flowering, and a higher seed set percentage, were also identified in this study. These discriminatory traits are discussed and proposed for germplasm conservation and use.

SUMMARYMaize (Zea maysL.), 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 ofStriga 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 underStriga-infested andStriga-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 underStriga-infested (Mokwa and Abuja) andStriga-free (Ikenne and Mokwa) conditions in 2010/11. TheStriga-resistant hybrids were characterized by higher grain yield, shorter anthesis–silking interval (ASI), better ear aspect, higher numbers of ears per plant (EPP), lowerStrigadamage rating, and lower number of emergedStrigaplants at 8 and 10 weeks after planting (WAP) compared with the susceptible inbreds. UnderStrigainfestation, mean grain yield ranged from 0·71 to 3·18 t/ha and 1·19 to 3·94 t/ha underStriga-free conditions. The highest yielding hybrid, TZEEI 83×TZEEI 79, out-yielded the OPV control by 157% underStrigainfestation. The hybrids TZEEI 83×TZEEI 79 and TZEEI 67×TZEEI 63 were the highest yielding under bothStriga-infested andStriga-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 F1hybrid underStrigainfestation 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 F1hybrids. However, a significant correlation existed between F1hybrid grain yield and heterosis underStrigainfestation (r=0·72,P<0·01). These hybrids have the potential for increasing maize production inStrigaendemic areas in WCA.

Accurate knowledge of intra-specific diversity of underutilized crop species is a prerequisite for their genetic improvement and utilization. The diversity of 77 accessions of African yam bean (AYB, Sphenostylis stenocarpa) was assessed by amplified fragment length polymorphism (AFLP) markers. A total of EcoRI/MseI primer pairs were selected and 227 AFLP bands were generated, of which 59(26%) were found to be polymorphic in the 77 accessions of AYB. The most efficient primer combination for polymorphic detection was E-ACT/M-CAG with a polymorphic efficiency of 85.5%, while the least efficient was E-AGC/M-CAG with a polymorphic efficiency of 80.6%. The Jaccard genetic distance among the accessions of AYB ranged between 0.048 and 0.842 with a mean of 0.444. TSs98 and TSs104B were found to be the most similar accessions with a genetic similarity of 0.952. The neighbour-joining dendrogram grouped the 77 accessions of AYB into four distinct clusters comprising 8, 20, 21 and 28 accessions. The major clustering of the accessions was not related to their geographical origin. Cluster I was found to be the most diverse. The mean fixation index (0.203) and the mean expected heterozygosity (0.284) revealed a broad genetic base of the AYB accessions. The same germplasm set was previously evaluated for several agro-morphological traits. As the collection of additional AYB germplasm continues, the phenotypic profile, the clustering of the accessions and the AFLP primer combinations from this study can be used to augment breeding programmes.

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