Starch Accumulation and Granule Size Distribution of Cassava cv. Rayong 9 Grown under Irrigated and Rainfed Conditions Using Different Growing Seasons

Although cassava can be planted throughout the year, its starch qualities may vary based on the date of planting. Seasonal variation on starch content, starch yield, starch granule size and amylose content of cassava cv. Rayong 9 grown under irrigated and rainfed conditions were studied for four planting dates in Thailand. A randomized complete block design with four replications was used in each planting. Planting dates consisted of hot-dry (20-Apr), early-rainy (30-Jun), late-rainy (5-Oct) and cool seasons (15-Dec). At final harvest, planting date accounted for the largest variations for starch yield (60.8%), starch granule size (38.2%), amylose content (50.5%) and ratio of amylose to amylopectin (53.7%), whereas starch content was affected more by water regime (52.1%). Supplemental irrigation did not significantly increase starch yield and other parameters for most planting dates, except for starch yield of the crop planted in the hot-dry season. This indicated that irrigation at the late-growth stages (during Sep to Mar) for the crop planted in the hot-dry season helped to increase starch yield: however, irrigation was unnecessary for other planting dates once cassava was established. The crops planted in the late-rainy and cool seasons had a greater starch content and starch yield than other planting dates for both irrigated and rainfed crops, whereas the crop planted in the hot-dry season had high starch yield for the irrigated crops only. In this study, the crops planted in the early-rainy season showed the worst performances for starch content and starch yield for both irrigated and rainfed crops. The data provided information on the responses of starch yield and its characteristics under irrigated and rainfed conditions at different planting dates, which can be useful for designing cultural practices with respect to water management and planting period in order to obtain optimum starch yield and qualities.