Pre-breeding of Bambara groundnut (Vigna subterranea [L.] Verdc.)
Bambara groundnut (Vigna subterranea [L.] Verdc.) is an under-utilized indigenous African legume crop which has substantial potential to contribute to food security in sub-Saharan Africa. The crop is well adapted to severe agro-ecologies and grows where other legumes may not survive. The seed is highly nutritious with an ideal balance of carbohydrate (55-72%), protein (18-20%) and fats (6-7% oil), which is particularly beneficial in balancing protein deficiencies in cereals. Also, the seed contains essential and non-essential amino acids of about 33% and 66%, respectively. These attributes make Bambara groundnut an ideal crop to alleviate food insecurity, and to reduce protein malnutrition in rural communities of Africa. However, small-scale farmers grow low-yielding landraces in most production regions in sub-Saharan Africa. Bambara groundnut landraces exist as heterogeneous mixtures of seeds of a few to several seed morpho-types that embrace wide genetic potential for breeding. The objectives of this study were: 1) to determine the production status and constraints associated with Bambara groundnut production in Kano State of Nigeria through the use of a participatory rural appraisal (PRA); 2) to determine the genetic diversity of Bambara groundnut landraces through seed morphology; 3) to assess the inter- and intra-genetic diversity of the Bambara groundnut landraces; 4) to determine the yield and yield component responses among selected Bambara groundnut genotypes, 5) to determine the genomic diversity in Bambara groundnut landraces, using simple sequence repeat (SSR) markers; and 6) to develop a crossing protocol. Using a structured questionnaire, 150 Bambara groundnut farmers were interviewed. The respondents interviewed were male and aged between 36 to 50 years, while Qur’anic education was the most popular among them. Most of the farmers practiced a combination of sole and mixed cropping, and allocated between 0.38 to 1.68 hectares of land to Bambara groundnut growing. They selected Bambara groundnut landraces, especially looking for large seeds that were pure and oval in shape, with a cream seed coat colour and which were early maturing. A total of 27 diverse landraces bearing different names were identified in the hands of the farmers. Most popular among them were Gurjiya, Kurasa, Hawayen-Zaki, Fara Mai-Bargo and Silva. Production was largely for home consumption and for sale on local markets. Common production constraints of the crop were identified as a lack of improved varieties (70.7%), frequent droughts (9.3%), low yield (4%) and limited access to large markets (3.3%). Diverse collections of Bambara groundnut landraces from seven geographic origins were characterized using seed morphology, including seed coat, seed eye colour and pattern, and hilum colour and pattern. Out of 58 original seedlots, a total of 353 different seed morpho-types were further identified. The selected morpho-types- can be used for large-scale production or true-to-type lines could be used in genetic improvement of the crop. Genetic variability within- and between-landraces was investigated among 262 Bambara groundnut landraces, forty nine were studied for agronomic traits, and 213 were investigated for pod and seed variability. Most (47.9%) of the landraces developed pods with a point on one pole, and a round end on the other. Most had a creamy (37.1%) and yellow (76.1%) pod colour, and the pods were usually rough textured, and contained an oval seed. A further 158 landraces were evaluated for leaf morphology where 49.4% had round leaves, while 21.5% had elliptic leaves, with 55.7% of the landraces being heterogeneous, possessing more than one form of leaf shapes. These discrete characters can be utilized for genetic studies and improvement of Bambara groundnut. Single plant selections of 49 Bambara groundnut genotypes were evaluated for yield and yield components using 26 yield and yield related traits. Highly significant variations (P<0.001) were detected among the genotypes for canopy spread, petiole length, weight of biomass, seed weight and seed height. Principal component analysis (PCA) identified nine useful components, where two components, PC1 and PC2, contributed strongly to the total variation, at 19% and 14%, respectively. The PCA revealed that leaf colour at emergence, petiole colour, leaf joint pigmentation and calyx colour were highly correlated with PC1, while seed length, seed width and seed height had strong association with PC2. Both the principal component and cluster analyses showed that most genotypes associated with one another with respect to agronomic and seed yield traits, irrespective of geographical location. The genotypes 211-57, MO9-4 and TV-27 displayed high seed yield performances, while TV-93 and 45-2 had higher biomass production. These genotypes can be used as breeding lines to enhance productivity of Bambara groundnut. Fifty Bambara groundnut genotypes, representing seven geographical regions across Africa, were genotyped using five pre-selected polymorphic simple sequence repeat (SSR) markers developed specifically for Bambara groundnut. The results detected a total of 53 alleles among the 50 Bambara groundnut genotypes, while the neighbor-joining analysis generated seven major genetic groups, which were clustered regardless of their geographic origin. Close relationship were found between 211-68 on one hand and 211-83-2, N211K and M09-3 with 211-68 on the other. Genotypes M02-3, 211-55-1 and 211-57 displayed close similarities. These associations suggested the likelihood that the two pair groups had common origins or may possess similar genes. A preliminary protocol was developed for crossing Bambara groundnut using eight selected parents, using the diallel mating system. Emasculation and crossing of Bambara groundnut was effective when conducted on the same day, with the two procedures being carried out sequentially between 4:30 am and 9:00 am. This protocol generated a number of F1 seeds, with the most success being from crosses between 211-40-1 x N211-2, N212-8 x 211-40-1 and M09-3 x 211-82-1. These F1 seeds can be advanced to confirm whether they are true F1 or selfs. The most important production constraint of Bambara groundnut production is the lack of improved varieties, suggesting that further breeding is needed to enhance productivity. Bambara groundnut landraces need to be sorted using discrete morphological features before breeding for genetic enhancement. The SSR markers used in the study demonstrated their ability to distinguish the existing diversity among the Bambara groundnut genotypes, which could be useful for both germplasm conservation and for breeding. Genotypes that displayed outstanding performance in seed yield and biomass can be used as breeding lines for the genetic improvement of Bambara groundnut. Overall, the study generated valuable and novel Bambara groundnut genetic material, useful in the development of improved cultivars for large-scale production in sub-Saharan Africa.
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