Abstract
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.
Highlights
Sweet potato, Ipomoea batatas L. (Lam.), is generally seen as a drought tolerant crop, but the selection for appropriate genotypes for drought conditions remains a priority
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% and 30% of the calculated water that the control treatment received in rainout shelters
Genotypic differences were observed for leaf area index (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
Summary
Ipomoea batatas L. (Lam.), is generally seen as a drought tolerant crop, but the selection for appropriate genotypes for drought conditions remains a priority. Leaf area index (LAI), which measures canopy cover as leaf area per unit ground surface area, is an indication of the leaf material in an ecosystem or trial area This can be an indication of the effectiveness of photosynthesis, estimation of soil water availability, and some other processes that might be a link between the plant and the environment (Bréda, 2003). It was noticed by Lewthwaite and Triggs (2012), with sweet potato cultivars planted in the field, that clones which showed a large reduction in canopy cover under water deficit experienced very large reductions in yield. It was noticed by Lewthwaite and Triggs (2012), with sweet potato cultivars planted in the field, that clones which showed a large reduction in canopy cover under water deficit experienced very large reductions in yield. Van Heerden and Laurie (2008) noticed large reductions in yield for cultivar Resisto which could be directly linked to low LAI values under water deficit conditions
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