Foliar application of uniconazole improves yield through enhancement of photosynthate partitioning and translocation to tuberous roots in sweetpotato

To examine the effects of uniconazole (UCZ) on the distribution and transport of photosynthate in sweetpotatoes, three spraying levels of UCZ, 0 (control), 50 and 100 mg L−1, were exposed to an experimental field cultivated with Jishu26 (‘J26ʹ) and Xushu32 (‘X32ʹ) varieties. Compared to control, the distribution of carbon-13 (13C) was significantly higher in the tuberous roots of both varieties treated with UCZ. In addition, UCZ treatments promoted a desirable top-to-base sucrose gradient and significant greater declines in the top-to-bottom amino acid and potassium ion (K+) gradients along the stem. Higher tuberous root yields were found in the UCZ-treated ‘J26ʹ and ‘X32ʹ. In comparison to 50 mg L−1 UCZ, ‘J26ʹ treated with 100 mg L−1 UCZ exhibited significantly higher distribution ratio of 13C in tuberous root, and reductions in the top-to-bottom amino acid and K+ gradients along the stems at 105 and 150 days after planting. Furthermore, 100 mg L−1 of UCZ application exhibited a significantly higher tuberous root yield. For ‘X32ʹ, the two concentrations of UCZ demonstrated no significant differences in these parameters. A reasonable distribution structure of photosynthates that responsible for high yields is associated with the desirable sucrose, ammonia nitrogen (N) or K+ gradient along the stems caused by UCZ application.