A Preliminary Study On Flowering Mechanism Of Root-Rotted Plants Of Sweet Potato

Root rot is one of the fungal diseases of sweet potato (Ipomoea batatas Lam.) in China. While most cultivars cannot flower in nature in Jiangsu, China, Shenglibaihao, a susceptible cultivar, flowers when infected by the root rot pathogen. In this study, ninety-three strains are isoalted from the rotted roots of flowering Shenglibaihao and are identified as Fusarium solani (Mart) Sacc. f.sp. batatas McClure (FSB). The FSB strain V100-93-06 induces Shenglibaihao to produce typical symptoms of root rot including flowering, resulting in shorten buds and lengthen roots, In the inoculation experiment, the disease index (0-2.8) increases as the inoculum concentrations increase from 1 103 to 1 105 spores/ml and as the time after inoculation increase from 10 to 40 days. The cultural filtrates of FSB on F-2 media (NH4NO3 10.0g, KH2PO45.0g, MgSO47H2O 2.5g, L-xylose 30g, H2O 1000ml) can induce similar symptoms. The seedlings show symptoms with disease index from 0.9-3.0 to 0 at 9th day after treatment with filtrates at different dilutions from 1:1 to 1:1010, respectively. Boiling for 10 min has no effect on the symptom induction of the cultural filtrate. The bioactive components) in the filtrate seems larger than 1000 dalton in molecular weight. The endogenous ABA concentration of leaf, shoot and root increase significantly in FSB infected sweet potato plants. The accumulation of ABA occurs firstly in root, and the highest concentration (1.0 pmol/gfw) occurs in shoot. The endogenous GA1/3 concentration of leaf, shoot and root of infected sweet potato keeps at a low level during the experiment period, and the GAi/3 concentration tends to decrease with the highest concentration at 4.1 nmol/gfw. hi addition, while ABA concentration in FSB mycelia is low (153.66 pmol/gfw), ABB concentration in the cultural filtrate of FSB is high (26.75 mg/1). Sweet potato tissue cultured seedlings increase significantly in ABA concentration 9hrs after treatment with FSB filtrate, while the ABA concentrations decrease and the GA1/3 concentration increases sharply at 15hrs. The disease symptoms may be induced by the changes of the concentration of ABA and GA1/3 in the tissue. The root rot sweet potato grows up right with being no tail, having air root in knots near ground and flowering widely at autumn.