FACULTY OF AGRICULTURE

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Assessing intraspecific variability and diversity in African yam bean landraces using agronomic traits
(MDPI, 2022-04) Olomitutu, O. E.; Abe, A.; Oyatomi, O. A.; Paliwal, R.; Abberton, M. T.
Landraces are repositories for potential beneficial traits which could be used to develop varieties with enhanced qualities. Optimal utilization of the available large collection of landraces of African yam bean (AYB) presently conserved at the Genetic Resource Center, International Institute of Tropical Agriculture, Ibadan (GRC-IITA), requires an assessment of the magnitude and nature of genetic diversity within the germplasm. One hundred and ninety-six AYB accessions were evaluated during the 2018 and 2019 cropping seasons in three agro-ecologies of Nigeria, using a 14 X 14 triple lattice design. The accessions were assessed for fourteen agronomic traits. Accession, environment, and accession X environment interaction effects were significant (p < 0.05) for all the traits. Variances due to environment and accession X environment interaction were higher than the genotypic variances. Similarly, estimates of phenotypic coefficient of variation (PCV) were higher than genotypic coefficient of variation (GCV) for all traits. Broad-sense heritability ranged from 17.1% (days to maturity) to 66.4% (seed length). Seed yield per plant had positive significant genotypic correlation with all the studied traits, except pod length and seed length. The first three principal components accounted for 59.7% of the total variation among the accessions and comprised of the 14 traits. Five major clusters were delineated based on phenotypic characteristics. Genetic variation was present among the AYB accessions, and these results will be useful for setting breeding goals and conservation approaches.
Genome-wide association study revealed SNP alleles associated with seed size traits in African yam bean (sphenostylis stenocarpa (hochst ex. A. rich.) harms)
(MDPI, 2022-12) Olomitutu, O. E.; Paliwal, R.; Abe, A.; Oluwole, O. O.; Oyatomi, O. A.; Abberton, M. T.
Seed size is an important yield and quality-determining trait in higher plants and is also crucial to their evolutionary fitness. In African yam bean (AYB), seed size varies widely among different accessions. However, the genetic basis of such variation has not been adequately documented. A genome-wide marker-trait association study was conducted to identify genomic regions associated with four seed size traits (seed length, seed width, seed thickness, and 100-seed weight) in a panel of 195 AYB accessions. A total of 5416 SNP markers were generated from the diversity array technology sequence (DArTseq) genotype-by-sequencing (GBS)- approach, in which 2491 SNPs were retained after SNP quality control and used for marker-trait association analysis. Significant phenotypic variation was observed for the traits. Broad-sense heritability ranged from 50.0% (seed width) to 66.4% (seed length). The relationships among the traits were positive and significant. Genome-wide association study (GWAS) using the general linear model (GLM) and the mixed linear model (MLM) approaches identified 12 SNP markers significantly associated with seed size traits across the six test environments. The 12 makers explained 6.5–10.8% of the phenotypic variation. Two markers (29420334|F|0-52:C>G-52:C>G and 29420736|F|0-57:G>T-57:G>T) with pleiotropic effects associated with seed width and seed thickness were found. A candidate gene search identified five significant markers (100026424|F|0-37:C>T-37:C>T, 100041049|F|0-42:G>C-42:G>C, 100034480|F|0-31:C>A-31:C>A, 29420365|F|0-55:C>G-55:C>G, and 29420736|F|0-57:G>T-57:G>T) located close to 43 putative genes whose encoding protein products are known to regulate seed size traits. This study revealed significant makers not previously reported for seed size in AYB and could provide useful information for genomic-assisted breeding in AYB.
Mechanism for pollination in African yam bean
(African Crop Science Society, 2016) Ojuederie, O. B.; Balogun, M. O.; Abberton, M. T.
African yam bean (AYB) (Sphenostylis stenocarpa (Hochst Ex. A. Rich) Harms is a neglected and underutilised legume in tropical Africa. Its utilisation has been hampered by the presence of anti-nutritional factors and lack of improved varieties. The objective of this study was to investigate pollination and determine the rates of selfing and outcrossing in the species. Accession TSs5 had the highest fruit set (63.16%) in the open-pollinated breeding method; while AYB50 had the lowest value (46.61%). Seed set in the selfed accessions ranged from 91.45% (AYB50) to 94.97% (TSs66). Fruit set was highest in the open-pollinated breeding method, with a mean average fruit set of 51.32%. Significant differences (P < 0.01) were obtained in fruit set from accessions isolated with net bags which had the lowest seed set (88.91%) Seed set was highest (92.92%) in the selfed accessions. The self incompatibility index ranged from 1.33 to 2.26 and the rate of fruit set from artificial self-pollination was greater than 30% in the field, and the screen house showing that the species is highly self compatible. Selfing and outcrossing rates of 91.38 and 8.62% showed that S. stenocarpa is not an obligate selfer. AYB sets fruits and seeds when open pollinated, isolated, selfed or crossed with other accessions.