Preliminary study on sweet potato growth: II. Sugar composition of developing storage roots.

The sugar composition in developing storage roots of sweetpotato (Ipomoea batatas (L.) Lam.) was studied for three cultivars, Owairaka Red (New Zealand), Beniazuma (Japan) and Beauregard (USA) which were grown in a replicated field trial at the Pukekohe Research Centre, New Zealand. Storage roots were harvested on 10 occasions, at weekly intervals from 71 days after transplanting (DAT) until 134 DAT. Roots from each harvest were analysed (HPLC) for their sugar content (fructose, glucose and sucrose). Root dry matter content was assessed by drying samples at 80°C for five days. While the three sweetpotato cultivars differed significantly in mean root dry matter content (P<0.001), they all showed an increase in percentage dry matter over time (P<0.001). Total sugar concentration (fructose + glucose + sucrose) increased linearly over time in both cv. Beniazuma and cv. Beauregard (P<0.001), but was essentially constant for cv. Owairaka Red (P=0.086). Sucrose was the predominant sugar in each cultivar, but the mean concentrations differed among cultivars (P<0.001). The relative proportions of sugar components for cv. Beniazuma were stable throughout plant growth, and sucrose concentrations were significantly (P<0.001) higher than in the other two cultivars. While root yield and size distribution are essential considerations for commercial sweetpotato production, root quality at a tissue level will become increasingly important in the development of novel products.