[Effects of exogenous plant hormones on physiological characteristics and yield of sweet potato under drought stress].

To explore the alleviation effect of spraying phytohormone on physiological characteristics and yield of sweet potato under drought stress in different periods, and to determine the best period of spraying external plant hormones, the effects on endogenous hormone content, photosynthetic fluorescence characteristics and yield of sweet potato were examined by spraying 6-benzylaminopurine (6-BA), α-naphthylacetic acid (NAA) and abscisic acid (ABA) respectively under drought stress after transplanting for 20 days (early stage), 60 days (middle stage) and 100 days (later stage) under artificial water control. The results showed that compared with spraying water, exogenous phytohormones significantly increased the yield of sweet potato under drought stress, among which 6-BA had the highest effect, followed by NAA and ABA. The effect of spraying in early stage was better than that in middle and late stages. Exogenous phytohormones significantly increased photosynthetic and chlorophyll fluorescence parameters of sweet potato leaves under drought stress at different stages, alleviated the decrease in eatin ribonucleoside (ZR) and auxin (IAA) caused by drought. Stepwise regression analysis showed that endogenous hormones and photosynthetic characteristics were key factors affecting yield of sweet potato. Results of path analysis showed that spraying exogenous plant hormone affected sweet potato yield by changing net photosynthetic rate (Pn), IAA, ZR, maximal photochemical efficiency and photochemical performance index under drought stress at early stage. Therefore, spraying 6-BA could regulate the content of endogenous hormones and improve photosynthetic characteristics of sweet potato at the early growth stage, and thus effectively alleviate the loss of yield caused by drought stress.