Yield of Drought-Stressed Sweet Potato in Relation to Canopy Cover, Stem Length and Stomatal Conductance

Sweet potato is generally considered as a drought tolerant crop, however, due to large genotypic differences, appropriate genotypes adapted to drought conditions must be identified. The aim of the study was to investigate the suitability of canopy cover, stem length and stomatal conductance to differentiate performance of sweet potato genotypes subjected to drought stress. Seven sweet potato cultivars and six elite lines were subjected to three water treatments, namely, a control (100%) treatment which received the full complement of plant available water (PAW) once soil water had depleted to 70% PAW, while the other two treatments received 60% (mild stress) and 30% (severe stress) of the calculated water that the control treatment received in rainout shelters. Pearson correlations were performed on measured parameters yield, leaf area index (LAI), stem length and stomatal conductance (gs). Genotypic differences were observed for LAI values and indicated that the cultivar Purple Sunset was better adapted to soil moisture stress at the mild stress and severe stress conditions than the other cultivars included in the trials. The cultivars Purple Sunset and Blesbok indicated a better ability to adapt to moisture stress, with regards to stem length, by outperforming the other genotypes in Trials 1 and 3. Drought had a severe effect on the yield of all the genotypes, especially at severe stress. Resisto, Bophelo and 199062.1 produced the highest yield at the mild stress, with significant correlations between yield and the parameters LAI, stem length and stomatal conductance. This indicated that above-ground growth had a direct influence on plant growth below-ground. The correlations also indicated that LAI and stomatal conductance played a more important role than stem length in achieving yield, and, thus, could be useful screening methods for drought tolerance of sweet potatato.