Genotypic variation in sweetpotato (Ipomoea batatas L.) in response to water deficit during plant establishment stage

Sweet potato is a short-term crop and is generally considered to be drought resistant. Reported drought resistant mechanisms for sweetpotato involved several traits such as maintenance of high leaf water potential and high root density. Under water stress conditions, biomass is highly dependent on water use (WU) and water use efficiency (WUE). Based on this idea, the growth responses of 18 sweetpotato genotypes under soil water deficit conditions were studied. The plants were grown in plastic pots (24.5 cm wide and 26.5 cm high) filled with sandy loam soil and placed under a plastic-covered rain shelter to manage the moisture content of the soil in the pots. All plants were established under well-watered condition (25% soil moisture content (SMC)) for 20 days. Then half of the plants were subjected to drought conditions by withholding water until 15% SMC was reached and maintained afterwards. The remaining control plants were continuously well-watered. Harvesting was done 31 days after drought imposition. Genotypic variation in reponse to limited water supply was significant. Plant traits affected by drought were shoot biomass, number of lateral stem, main vine length, number of leaves, leaf water potential, stomatal resistance and transpiration rate. Biomass production was significantly reduced in drought-treated plants. Drought resistance was evaluated as the ratio of biomass of drought-treated plants against control. The ratio ranged from 0.13 to 0.42. The drought treatment significantly reduced WU by 68%, while it tended to increase WUE by an average of 5% across genotypes. Two genotypes with greater drought resistance namely: Makapuling and PSB Sp-16 maintained high predawn and midday leaf water potential and midday stomatal resistance. It could be inferred therefore, that in these genotypes, higher stomatal resistance and leaf water potential particularly at midday resulted in increased WUE and biomass production under drought. Involvement of other morphological and physiological traits in WU were also discussed