Evaluation of yam bean (Pachyrhizus spp.) accessions for root yield and nutritional quality under different agro ecologies in Uganda.
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Yam bean (Pachyrhizus spp.) is one of the legume root crops that is exclusively used for its storage roots. The yam bean has three closely related cultivated species: P. tuberosus (Lam.) Sprengel, P. erosus (L.) Urban, and P. ahipa (Wedd.). It produces large storage roots like cassava or sweetpotato, which are consumed raw, cooked or processed. However, its seeds are inedible due to the presence of toxic rotenone. Flowers are often pruned to increase storage root fresh yield. The objectives of this study were to determine root yield performance, stability, yield components, and the root nutritional quality of selected yam bean accessions in different agro-ecological zones of Uganda. A total of 25 yam bean accessions were tested on station in three distinct locations namely, Namulonge (1150 m.a.s.l.), Serere (1140 m.a.s.l.), and Kachwekano (2220 m.a.s.l.) in the first and second seasons of 2011. Significant (P > 0.05) differences in fresh storage root yields were observed across the different locations with the ideal location being Namulonge (fresh storage root yield of 10.05 tha-1), followed by Serere (8.0 tha-1), and the worst performing location was Kachwekano (3.08 tha-1). Fresh storage root yields were also significantly (P > 0.05) different among genotypes. AMMI analysis showed the presence of genotype-by-environment interaction for fresh yam bean storage root yield. Through AMMI estimates and GGE, accession 209017 was the highest yielding at all the locations with mean yield of 20.68 tha-1 and accession 209018 with mean yield of 15.48 tha-1 was the most stable and adapted accession in the discriminating environments used in the evaluation of yam beans in Uganda. All yield components (number of storage roots per plant, proportion of big roots, proportion of small roots, and fresh weight of vines and leaves in tha-1) were significantly (P > 0.05) different across accessions except total number of storage roots. Total number of storage roots, number of storage roots per plant, root weight, vines and leaves are important yield components to target in yam bean improvement. Nutritional traits significantly varied across locations and among accessions. Yam bean storage roots had high protein (9.56%), starch (53.01%), iron (19.31 mg/kg), zinc (16.99 mg/kg), calcium (1470 mg/kg), potassium (13037 mg/kg) and phosphorus (2760 mg/kg) but low dry matter (15.97%). The higher storage root dry matter of 20.31% was observed in accession 209024. The performance and stability of yield of yam bean within this study highlights its potential to grow in Uganda