Comparison of root development and fluorescent physiological characteristicsof sweet potato exposure to drought stress in different growth stages

【Objectives】To clearity the water critical period of sweet potato will provide scientific basis to find effective way against drought and optimization of production and management of sweet potato. 【Methods】 A pot experiment was conducted inside an artificial drought shed. Three drought stress (8%-10% field water capacity, stress lasted 15 days for each treatment) was designed at early, middle and late stages of sweet potato (15, 55 and 95 days since transplanted). The root development was measured using Epson v700 Scannor, and the fluorescence physiological parameters using M-PEA(Hansatech,Britain)method. 【Results】The shoot and root biomass of sweet potato were significantly reduced when exposure to drought stress at both the early and middle growth stages (P 0.05), but not significant at late stage drought stress, and the reducing effect was in order of early stage＞middle stage＞late stage. Compared with the control, the shoot and root biomass were reduced almost in half in the early stage stress, and decreased by 38.4% and 31.1% at middle stage stress, and less than 10% in the late stage stress for aboveground and underground parts. Drought stress affected root development, compared with the normal water supply. Early drought stress decreased the length, surface area and volume of root by 49.5%, 55.7% and 43.2% respectively, the middle stage decreased by 27.5%, 27.0% and 28.9% respectively, and late stage had less effect. The influence of drought stress on the chlorophyll fluorescence parameters was different when stressed in different periods, the significant impact was found in early stage and medium stage, not in later stage. Compared with CK, the comprehensive chlorophyll fluorescence of PSⅡ, Fm, Fv/Fm and PI(ABS) at early and middle stage were decreased by 36.4%, 15.6%, 44.3% and 14.7%, 3.8%, 22.6% respectively, the φEo value decreased by 7.7%, 3.4% respectively, Vj and dV/dto increased by 33.1%, 32.1% and 19.2%, 17.1% respectively. 【Conclusions】The changes of fluorescence parameters reflected the PSⅡ structure damage and reaction center hurt caused by drought stress, which indicated the resulted blockage of light energy conversion efficiency and electron transfer. The adverse impact is mainly happened when sweet potato is suffered from drought stress in the early and middle growth stages. Therefore, proper irrigation should be considered in case of drought climate in seedling stage of sweet potato.