Impact of water stress on yield and quality of cassava starch

Abstract

Cassava ( Manihot esculenta Crantz) is an important source of industrial raw materials. Products obtained from cassava include chip/pellets for animal feed and starch. Important for major industrial uses are the amount and quality of starch obtained from this crop. Production efficiency, including yield and quality of starch, from cassava is markedly influenced by environmental conditions, especially water stress during early plant development and immediately before root harvest. In early plant development plants deprived of water for the first 6 months were characterized by a lower yield of starch compared to plants without water stress (starch yields of six varieties including Rayong 1, Rayong 5, Rayong 60, Rayong 90, Kasetsart 50 and CMR 33-57-81 were 0.1–0.2 and 5.0–8.7 t/ha for water-stressed and without water-stressed plants). Furthermore, starch from plants deprived of water for the first 6 months of growth, was functionally different to that laid-down under optimum growing conditions. Plants responded to subsequent rainfall and after 2 months contained significant amounts of starch, though this amount was less than was expected. Despite the fact that water-stressed plants responded to the availability of water by producing starch, most functional properties remained different. The portfolio of changes was sufficient as regards the starch of lower quality. Most effected were the hydration properties. Starch granules despite being smaller (mean size and distribution) than expected were morphologically normal. A second drought period further influenced some of the starch properties, but the sustained influence of the early drought seemed to dominate the response of the plant's starch metabolism. All varieties were similarly affected.