Difference and Related Reason for Assimilate Distribution of Sweetpotato Varieties with Different Root Tuber Yields

Abstract

A field experiment was conducted at agricultural experiment station of Shandong Agricultural University, Tai'an, Shandong Province in two growth seasons of 2011 and 2012. Six typical varieties of edible sweetpotato in North China were used, including Longshu 9, Hongxiangjiao, Taizhong 6, Sushu 8, Yizi 138, and Beijing 553, to study the difference and reason for assimilate distribution among varieties with different yield levels. The distribution characteristics of assimilate was studied by 13 C labeling during storage roots development; sucrose content of different stem parts and stem base diameter were measured as well. And the relationship between the above traits and harvest index, root tuber yield was also analyzed. The results showed that the root tuber yield of high-yielding varieties(Longshu 9, Hongxiangjiao, Taizhong 6, and Sushu 8) was about 60 t hm–2, whereas that of intermediate and low-yielding varieties(Yizi 138 and Beijing 553) was less than 50 t hm–2. And the harvest index of high-yielding varieties was significantly higher than that of intermediate and low-yielding varieties. The root tuber of high-yielding varieties became assimilate distribution center at early bulking stage, while for intermediate and low-yielding varieties that was at late bulking stage; and high-yielding varieties also had significantly higher 13 C distribution rate than that of intermediate and low-yielding varieties, indicating that high-yielding varieties had relatively higher ability to transport assimilate from functional leaves to root tubers. Sucrose content of stem base was higher than that of stem top, and the sucrose concentration gradient of intermediate and low-yielding varieties was higher than that of high-yielding varieties. Low-yielding varieties' stem base thickened faster than high-yielding varieties in the development of sweetpotato. The correlation analysis showed that root tuber yield had significantly positive correlation with harvest index(r = 0.98**, 2011; r = 0.93**, 2012). Root tuber yield and harvest index had significantly positive correlation with 13 C distribution rate of root tuber(0.87* and 0.91**, 2011; 0.92** and 0.99**, 2012); they also had significantly negative correlation with stem base diameter during middle and late growth stages(–0.78* and –0.83*; –0.88** and –0.95**). Therefore, high-yielding varieties got higher harvest index mainly due to less time taken by their root tuber to become assimilate distribution center and stronger ability of assimilate transportation from functional leaves to root tubers; and low-yielding varieties got lower abilities of assimilate transportation mainly because assimilate unloading in root tubers was not smoothly.