Abstract
The American yam bean (Pachyrhizus spp.) is a legume crop that is exclusively used for its storage roots. The seeds are inedible due to presence of toxic rotenone. It produces high storage root yields comparable of major root crops like cassava or sweetpotato. And flower pruning more than doubles its root yield performance. Using twenty five yam bean accessions, the current study aimed to determine root yield stability and adaptability, and presence of yam bean production mega environments in Uganda. Trials were planted at three stations, Namulonge, Serere, and Kachwekano during two consecutive seasons of 2011. Fresh storage root yields were significantly different (p < 0.05) across locations with the ideal location being Namulonge (fresh storage root yield of 10.1 t ha-1), followed by Serere (8.0 t ha-1), and Kachwekano (3.1 t ha-1). Results of AMMI analysis indicated the presence of genotype-by-environment interaction for fresh storage root yield. Through AMMI estimates and GGE visual assessment, genotype 209017 was the highest yielding with mean yield of 20.7 t ha-1. Genotype 209018 with mean yield of 15.5 t ha-1 was the most stable and adapted accession in the entire discriminating environment in Uganda. From the environmental focusing plot, the six environments were grouped into two putative mega environments for yam bean production.
Highlights
The American yam bean (Pachyrhizus spp.) is an underutilized legume crop in the tropics and subtropics producing large storage roots (Jacobsen, Sørensen, Pedersen, & Weiner, 2015)
The study was conducted at three locations representing different agro-ecological zones of Uganda (Table 1), namely Namulonge in the lake Victoria crescent zone area [1150 m.a.s.l., at the National Crops Resources Research Institute (NaCRRI)], Serere in the north east savanna zone of Uganda [1140 m.a.s.l., at the National Semi Arid Resources Research Institute (NaSARRI)], and Kabale in the south western highlands of Uganda [2220 m.a.s.l., at Kachwekano Zonal Agricultural Research and Development Institute (KaZARDI)]
The low means of fresh storage root yields obtained at Kachwekano in this study probably suggest that it is less suitable for yam bean production compared to Namulonge and Serere
Summary
The American yam bean (Pachyrhizus spp.) is an underutilized legume crop in the tropics and subtropics producing large storage roots (Jacobsen, Sørensen, Pedersen, & Weiner, 2015). Like its close relative the soybean (Glycine max [L.]) (Ndirigwe et al, 2017), the yam bean produces large amounts of seeds. The seeds of the American yam bean are not edible to humans because they contain rotenone and pachyrhizin in toxic quantities (Sørensen, 1996; Ndirigwe et al, 2017). In both small scale and commercial production, the crop is grown exclusively for its storage roots (Sørensen, 1996) and all the flowers are removed, as flower pruning increases storage root production by about 100% (Rizky, Hasani, & Karuniawan, 2013). Only a few plants are not flower pruned to produce seeds for the crop production
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