African yam bean (AYB) belongs to the family Fabaceae. It is an orphan crop with so many potentials that have not been well utilised. It produces both edible seeds and tubers with high nutritional values. However, the crop is grown mainly for the seeds in West Africa, but the tubers are mainly consumed in East and Central Africa. The dual food advantage of AYB is yet to be fully tapped, due to the irregular tuberization in accessions. This study therefore characterised tuber development in AYB accessions in vitro and on the field, visually and microscopically. The proximate analysis of the seeds and tubers of AYB accessions were also evaluated. Three tuber-forming (TSs 96, TSs 107, and TSs157) and three non-tuber forming (TSs 51, TSs 150, and TSs 152) accessions of AYB were collected from the Genetic Resources Centre of the International Institute of Tropical of Agriculture, Ibadan, Nigeria and evaluated on the field at two different periods: (June – December 2020) and (September 2020 – March 2021) for agromorphological traits. The field was laid out in a randomized complete block design (r = 3). Data was collected at peduncle initiation (50%, 75% and 100%), flowering (50%, 75% and 100%), and physiological maturity through destructive sampling. A microscopic cross image sectioning of freshly harvested AYB tubers was assessed using standard procedures. The six AYB accessions were evaluated in vitro in a completely randomized design (r=20) using a medium containing 4.43 g L-1 MS (Murashige and Skoog), 0.6 mgL-1 BAP (Benzyl amino purine), 0.03 mgL-1 NAA (Naphthaleneacetic acid), 0.1g L-1 Myoinositol, varying concentrations of Sucrose (30 gL- 1, 50 gL-1, 70 gL-1) and 7 gL-1 agar for microtuber formation. Proximate analyses of seeds and tubers produced were determined using standard procedures. Data were analysed using descriptive statistics and ANOVA at α0.05. TSs 107 was the only accession that produced tubers from 75% peduncle initiation to physiological maturity. Accessions that failed to produce tubers had few root nodules with less dense root architecture compared to TSs 107 which had the highest root nodule production with thicker root structure. A cross microscopic section imaging of the freshly harvested tuber of TSs 107 indicated that AYB tubers are derived from stem hypocotyl and not formed from the root. Analysis of variance of accessions planted in June 2020 indicated that pod length ranged from 22.1 ± 3.0 cm (TSs 152) to 25.3 ± 4.6 cm (TSs 107) and the number of seeds per pod ranged from 14.9 ± 4.0 (TSs 107) to 17.3± 2.5cm (TSs 157). Seed yield ranged from 9.3 ± 2.5 g (TSs 51) to 154.5 ± 12 g (TSs 96). TSs 107 which produced tubers had low seed yield (26.98 ± 4.83 g) and the longest number of days to first flowering (109 days) which was significantly different from TSs 96 (94 days) and TSs 157 (93 days). Nodulation in June 2020 was significantly highest in TSs 107 at both peduncle initiation (54.32) and flowering (43.56) stages of growth with the least number of nodules at both stages of growth (16.56 and 5.48) produced by TSs 152. Nodulation was significantly higher in accessions planted in June 2020 (10.69 ± 3.11) compared to those planted in September 2020 (0.38 ± 0.42). The moisture content in AYB seeds ranged from 9.63 ± 0.05% (TSs 152) to 10.17 ± 0.18% (TSs 51). The tuber of TSs 107 had lower moisture content (6.05 ± 0.22%) compared to the seeds (10.05 ± 0.10%). The crude protein in seeds ranged from 15.34 ± 0.70% (TSs 51) to 19.64 ± 0.08% (TSs 150) while the carbohydrate content ranged from 60.09 ± 0.16% (TSs 150) to 70.08 ± 0.54% (TSs 51) respectively. Only TSs 107 produced tubers out of the three tuber producing accessions. Accessions planted in June 2020 produced seeds, much nodules and tubers compared to those planted in September which failed to produce seeds, but TSs 107 produced tubers. Therefore, AYB accessions should be planted in the appropriate planting season (June) to avoid abortion of flowers during the late planting season. Nodulation decreased from vegetative stage to physiological maturity in all accessions. An inverse relationship exist between protein and carbohydrate contents in AYB seeds as observed in TSs 51 and TSs 150. The seeds of TSs 107 had higher protein content (17.65%), but the tubers still had appreciable amount of protein (15.41%).

All glory to God for making it possible for me to embark on this research and successfully complete it. I am indeed very grateful to my supervisor, Prof. Morufat O. Balogun of the Department of Crop Protection and Environmental Biology, University of Ibadan, and Prof Michael Abberton, Head of the Genetics Resources Centre, International Institute of Tropical Agriculture (IITA) for accepting me as a Research Fellow at IITA, and their selfless supervision and encouragement, especially during ...

Agronomy; Food Security; Genetic Improvement; Plant Breeding; Plant Production; Yam

African Yam Beans; Sphenostylis Stenocarpa; Yields; Varieties

Africa; West Africa

Nigeria

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