Yam (Dioscorea spp.) is a valuable food security crop in West Africa, where 92% of the world production occurs. The availability of quality seed tubers for increased productivity is a major challenge. In this study, minitubers weighing 1, 3, and 5 g produced from virus-free single-node vine cuttings of two improved yam varieties (Asiedu and Kpamyo) growing in an aeroponics system were assessed for suitability in seed production at a population of 100,000 plants ha⁻¹. A 3 × 2 factorial experiment with randomized complete block design and three replications was set up during the cropping seasons of 2017 to 2019 at the International Institute of Tropical Agriculture Research Station in Kubwa, Abuja, Nigeria. Results showed field establishments of 87%–97.8%. Yields differed with minituber size, variety, and cropping season; the highest was 31.2 t ha⁻¹ in 2019 and the lowest, 10 t ha⁻¹ in 2018 from 5 and 1 g Kpamyo minitubers, respectively. The estimated number of tubers produced per hectare by 1, 3, and 5 g minitubers was 101,296, 112,592, and 130,555, with mean weights per stand of 159.2, 187.3, and 249.4 g, respectively. We recommend using less than 6 g minitubers for seed yam production due to their high multiplication rates.

The availability of clean planting materials and functional seed regulatory systems is indispensable for fostering a sustainable seed yam system. The Yam Improvement for Income and Food Security in West Africa (YIIFSWA) project of the International Institute of Tropical Agriculture (IITA) developed the capacity of National Agricultural Research Institutes (NARIs) in their use of standardized Temporary Immersion Bioreactor (TIB) and Vivipak (VP) systems for high-ratio propagation and post-flask handling of yam breeder seed plantlets. Foundation seed was enhanced by supporting five private seed companies in Nigeria and three in Ghana. They were equipped with aeroponic and hydroponic technologies for foundation seed tuber production using single-node vine seedlings. For certified seed, seed yam out-growers were trained in good agronomic practices and entrepreneurship for certified seed tuber production using the adaptive yam minisett technique (AYMT). New certification standards were established for various classes of seed produced using different propagation methods and quality assurance procedures in Ghana and Nigeria. The capacity of the national regulatory organizations in both countries was enhanced to implement seed quality control and certification. Increased public sensitization and advocacy were done to raise awareness among relevant stakeholders to enhance the uptake of the seed propagation technologies and ensure a smooth interaction between the public and private sectors. This chapter summarizes the accomplishments of YIIFSWA in Ghana and Nigeria and the spillover impact on the yam belt of West Africa and beyond. The key lessons could inform the design and implementation of more effective seed projects, especially for vegetatively propagated crops.

Yam is a staple crop in Africa that is constrained by its low multiplication rate. This results in a short supply of seed tubers, which is a challenge to increased production. This study assessed the influence of different minisett weights (10, 20, 30, 40, and 50 g) on tuber production and seed categorization in twelve Dioscorea rotundata and four Dioscorea alata varieties over two planting seasons in a Randomized Complete Block Design (r = 3). The yield parameters were collected and analyzed using ANOVA. The effects of varieties, the minisett weight (SW), and the variety × SW interaction were significant for the proportion of setts that produced seed tubers and ranged from 40.2 ± 5.0% (50 g) to 56.4 ± 5.0% (10 g) in 2013, from 46.4 ± 0.8% (40 g) to 60.5 ± 0.8% (30 g) in 2014, from 23% (TDa00/00194, 30 g) to 93.7% (Ojuyawo, 10 g) in 2013, and from 39.7% (TDa00/00194, 30 g) to 100% (TDr89/02665, 20 g) in 2014. The 10 g and 30 g produced more seed yam in 2013 and 2014, respectively, while 50 g produced more ware yam sizes (>300 g) and is thus recommended to farmers for intended yam production category. D. rotundata varieties produced a higher proportion of seed yam, while D. alata varieties produced are a higher proportion of yams above seed class.

Maize is a staple food of sub-Saharan African (SSA) populace but deficient in protein. Quality protein maize (QPM) has been developed to contain essential amino acids including lysine and tryptophan to alleviate malnutrition in SSA. This study was conducted to assess general and specific combining ability (GCA and SCA) effects, gene actions and heterosis among QPM hybrids for lysine and tryptophan at three locations in humid agro-ecologies of Nigeria. Grains from sib-mated full-sibs were analysed for lysine and tryptophan among ten inbreds, 45 hybrids generated by half-diallel and two checks. Results showed lysine and tryptophan contents ranged from 2.71% - 0.73% (Kishi) to 3.41% - 0.96% (Ibadan). Gene actions for expression of lysine and tryptophan varied with location; thus, additive gene action was preponderance in inheritance of lysine and tryptophan in Ibadan and Ile-Ife, whereas non-additive gene action was involved in inheritance of these traits in Kishi. Inbreds TZEEQI-8, TZEEQI3, TZEEQI-10, TZEEQI-12, TZEEQI-2 were best combiners for lysine and tryptophan. Hybrids TZEEQI-8?TZEEQI-16, TZEEQI-2?TZEEQI-12, TZEEQI 10?TZEEQI-7,TZEEQI-10?TZEEQI-12 and TZEEQI-8?TZEEQI-12 were adjudged as the top five hybrids for exhibiting positive and significant standard heterosis over commercial check with a range of 12.8%-16.7% for lysine and 15.4%-20.0% for tryptophan across locations. The relationship between grain yield with lysine and tryptophan was negative and significant across locations. Hence, breeding for high yielding QPM genotypes with high lysine and tryptophan contents at the same time, requires careful monitoring of lysine and tryptophan contents in the laboratory.

The second phase of the Yam Improvement for Income and Food Security in West Africa (YIIFSWA II) project was implemented through a strong collaboration between research and private sector. Private seed companies were provided with a wide variety of training and development activities on good agronomic practices (GAPs). However, the effects of the training activities were yet to be evaluated. This paper evaluated the contribution of the training on high-quality seed yam production through paying particular attention to how it was tailored to the needs of various farmers, and how the knowledge gained was transferred to the field. The study employed an applied Kirkpatrick model and descriptive statistics to measure the indicators of training effectiveness. Results from a statistical population of 172 farmers using 179 demonstration fields showed that the farmers’ training on GAPs was effective, based on four criteria of the Kirkpatrick training evaluation process. The satisfactory results at the beginning of the hierarchical model have implications on the satisfactory results at the end. Improving the effectiveness of a training depends on defining factors such as (i) Training based on satisfaction in meeting the needs of your trainees and the seed production business; (ii) Training based on learning objectives in improving the trainees’ skills and knowledge; and (iii) Training based on learner attitude change in applying new skills and knowledge in the fields. Conclusions drawn from this study indicated that the training was a reasonable value-added mechanism of improved agricultural knowledge and practices for enhancing high-quality seed yam production in Nigeria.

In vitro propagation of yam via organogenesis is constrained with low multiplication rate. Somatic embryogenesis (SE) has shown rapid multiplication potentials in yam. However, it has not been adopted by practical seed system scenarios due to genotype specificity. Reports have shown that SE is regulated endogenously by phytochemicals, but this is yet to be elucidated for yam. This study identified, quantified endogenous, and evaluated effects of exogenous application of selected identified phytochemicals in yam SE. Callus was induced from in vitro axillary bud explants of three Dioscorea rotundata genotypes in Murashige and Skoog (MS) medium containing 9.1 µM 2,4-dichlorophenoxyacetic acid and 5.4 µM naphthaleneacetic acid. Plantlets were regenerated using MS medium containing 4.4 µM benzylaminopurine and 34.0 µM uniconazole-P. Endogenous phytochemicals associated with axillary bud, calluses, and plantlets were identified and quantified using GC/MS. Effect of selected identified phytochemicals on the genotypes was investigated in a 5 × 6 factorial in completely randomized design (r = 3). Data taken on plantlet regeneration was analyzed using ANOVA at α_0.05. A total of 27, 22, and 35 phytochemicals were identified in Kpamyo, Ekiti2a, and Asiedu, respectively. Hexamethylcyclotrisiloxane (36.4%, Kpamyo), Tris-tert-butyldimethylsilyloxy-arsane (59.3%, Ekiti2a), and 4-methyl-2-trimethylsililoxy-acetophenone (52.7%, Asiedu) were highest in callus. N-Methyl-1-adamantaneacetamide (31.8%, Kpamyo) and Tris-tert-butyldimethylsilyloxy-arsane (52.7%, Ekiti2a, Asiedu) were highest in plantlets while Tris-tert-butyldimethylsilyloxy-arsane (41.2%, Kpamyo), hexamethylcyclotrisiloxane (55.8%, Ekiti2a), and erythro-9,10-dibromopentacosane (38.9%, Asiedu) were highest in axillary bud. Plantlet regeneration differed significantly among phytochemicals and ranged from 0.7 ± 0.3 (control) to 4.5 ± 0.5 (40.5 µM phenylacetic acid). Also, genotype × phytochemical interactions on number of plantlets regenerated were significant, and mean values ranged from 0.0 ± 0.0 (TDa2014, 4.8 µM decamethyltetrasiloxane) to 7.0 ± 1.7 (TDa2014, 40.5 µM phenylacetic acid). The application of 40.5 µM phenylacetic acid enhanced plantlet regeneration in Kpamyo and TDa2014 by 5.39% and 343.04%, respectively.