Adventitious root formation is dynamically regulated by various hormones in leaf-vegetable sweetpotato cuttings

Leaf-vegetable sweetpotato is an important cash crop that is of high nutritional value. Cuttage is the most convenient method for large-scale propagation. However, the rate and number of adventitious roots (ARs) formation vary significantly among different cultivar cuttings. In this study, two varieties, NC1 and FC13-14, were used to compare the rate of ARs formation. The cumulative results of root morphology showed that in NC1 total root length, total root surface area, total root volume, and root tips were 3.7, 3.5, 3.2, and 2.4 times greater, respectively, than those of FC13-14 at 7 d, indicating that the ARs formation and growth were faster in NC1. In addition, the biomass of aboveground and underground parts in NC1 was 3.6 and 1.3 times more, respectively, than that of FC13-14 at 7 d after cutting, suggesting that the rapid ARs formation rate contributed to the growth and yield of stems and leaves. The analysis of plant water potential showed that NC1 exhibiting higher water potential prevented leaf wilting. Gene expression levels of 22 root-related genes revealed differential expression during different developmental periods. Interestingly, YUCCA family genes had elevated transcript abundance at 0, 12, 24, and 36 h. Moreover, analysis of hormones including indole-3-acetic acid (IAA), ethylene (ETH), abscisic acid (ABA), brassinolide (BR), jasmonic acid (JA), gibberellin (GA), and cytokinin (CTK) revealed varied contents during different developmental stages. Cumulative evidence demonstrated that gene expression profiles and hormone content of IAA, ETH, and BR were significantly higher in NC1 roots than in FC13-14 roots following all time periods, while the amount of JA increased and was higher in FC13-14 than in NC1 from 0 to 72 h. This indicates that IAA, BR, and ETH play positive roles and JA has a negative effect on ARs formation. Moreover, ETH takes effect earlier than BR, while IAA and JA have functions throughout the whole process. The findings above were validated by the application of exogenous hormones and hormone synthesis inhibitors. This study reveals the preliminary regulation of ARs formation in leaf-vegetable sweetpotato cuttings and thus contributes to further clarification of the molecular mechanism of multiple hormone interactions.