Screening sweetpotato genotypes for tolerance to drought stress

Soil moisture stress due to drought results in low storage root yield of sweetpotato. Eighty-four sweetpotato clones were evaluated at Kenya Agricultural Research Institute (KARI), Kiboko and Thika between May 2011 and September 2012 for drought tolerance. A split plot design with drought stress and no drought stress conditions as whole plots, and clones as subplots, arranged in a 14 x 6 alpha lattice design with two replicates repeated in two seasons was used. Approximately 30 cm long vine cuttings of each clone were planted I 0 cm deep on 25 cm high beds, in single rows of 6 hills spaced at 30 x 90 cm. The field study was also validated in screenhouse box experiments at KARI-Muguga. Data on growth and yield characteristics were recorded and analysed using SAS 9.2 edition. Across sites, data indicated that genotype, environment, and their interaction significantly differed for fresh storage root weight (FSR) (kg plant(-1)), total fresh biomass weight (FB) (kg plant(-1)), marketable fresh storage root weight (MFSR) (kg plant(-1)), harvest index (HI) and chlorophyll content (CC) (8.47%) at (P <= 0.05). Comparing data from both environments, drought stress caused a reduction of FSR (59.3%), FB (72.1%), MFSR (75.5%), NSR (25.6%), but seemed to increase percent root dry matter (%RDM) (-0.29%), and HI (-26.6%). Clones 194555.7, Unawazambane06-01, 189150.1, Tanzania, Chingova, W119, 441725, and Xiadla-xa-kau, had >= 75 days to permanent wilting point (DPWP), drought stress index (DSI) <1 and high FSR yield under drought stress and no drought stress conditions. These clones may be used in a drought tolerance breeding programme. Clones that had low DSI values, also had low FSR yield difference under drought and no drought environment, indicating they were drought tolerant, but had less DPWP. However, high yielding clones under no drought, also had relatively high yield difference between drought and no drought environments, and high DSI values, which implied less drought tolerance. Thus, DPWP demonstrates high discriminative power to identify clones with both drought tolerance and improved yielding ability, especially in root crops such as sweetpotato, which occasionally produce pencil roots instead of edible storage roots even under adequate moisture conditions. (C) 2014 Elsevier B.V. All rights reserved.