Impacts of cultivation practices on internal browning in sweetpotato

Abstract

ABSTRACTA disorder of sweetpotato, characterised by abnormal brown colouration inside the storage root, began to occur around 2006. The aims of the present study are to test our previous hypothesis that IB disorder occurs due excessive starch synthesis inside the storage root at the maturation stage and to present a technique for inhibiting IB disorder based on experimental findings. The severity of internal browning (IB) disorder in sweetpotato was greater when larger root biomass was achieved by vigorous top growth through increased basal fertiliser application. In contrast, suppression of root growth by defoliation at the early stage of root maturation and/or through shading during the maturation stage was correlated with marked suppression of IB disorder. Expression profiling of genes involved in starch synthesis and starch grain distribution around secondary vascular tissue were examined for shading treatment samples. Transcription levels of genes related to starch synthesis were decreased in the shade treatment. Further, the starch grain content as an area percent in the cells was reduced through shade treatment. These observations suggest that the occurrence of IB disorder is largely affected by the degree of activation of starch synthesis utilising sugar transported to the root.Abbreviations: IB: internal browning; DAP: days after planting; T/R: top/root; rbt: ratio of browned to total tissue