Abstract

Breeding sweetpotato [Ipomoea babatas (L.) Lam] for drought tolerance requires inexpensive, reproducible and high throughput screening systems. The objective of this study was to apply greenhouse and in vitro techniques to select drought tolerant sweetpotato genotypes. Greenhouse and in vitro experiments were established at Rubona Research Station of the Rwandan Agricultural Board using 54 sweetpotato genotypes. Genotypes were evaluated in the greenhouse using four levels of water regime [control, drought stress imposed by withholding water for one, two or three month(s)], while in vitro tests were carried out using four treatment solutions [control or basic culture medium (0 M), control supplemented with 0.2, 0.4 or 0.6 M sorbitol]. In the greenhouse study, data collected included: soil water potential (ψ w), weights of storage root, biggest storage root and vines, dry matter content (DMC) of storage root and vine and water content (WC) of vines. Whereas ψ w of culture media, fresh weight gain (FWG), DMC and WC were recorded during the in vitro experiment. In the greenhouse test, ψ w of drought stressed treatments varied from-1.94 to-0.05 MPa and showed an increased trend with prolonged drought stress. The control treatment showed ψ w ranging between-0.02 to 0 MPa. During the in vitro experiment, the mean ψ w were-0.07, -0.81, -1.35 and-1.73 MPa for control, 0.2, 0.4 and 0.6 M sorbitol treatments, respectively. Under greenhouse condition, genotype by water regime, genotype and water regime had significant effects (P≤0.01) on yield and yield related traits. Genotypes showed significant differences between the control and drought stress imposed for one month. Under in vitro test, the control and 0.2 M sorbitol treatments were not significantly different in the FWG. However, the control treatment was significantly different from 0.4 and 0.6 M sorbitol concentrations. Positive correlations were observed between vine yield and FWG; and between total biomass and FWG, during greenhouse and in vitro studies, respectively. Overall, genotypes 2005-146, 4–160, 8–1038, Kemb 37, Kwezikumwe, Purple 4419, NASPOT 9, Nsasagatebo, Karebe, 440037, Mwanakumi, 97–062 and Matembere were selected with comparatively high drought tolerance using the two screening procedures. The selected genotypes are useful genetic resources to breed sweetpotatoes for drought tolerance.