Effect Of Exogenously Added Hexadecanoic Acid On Watermelon Growth And Microbial Of Continuouscropping Soil

Watermelon is the world horticultural crops, it is the largest producer of watermelon in world. Chinese watermelon cultivation area is the first in the world. With the increase of watermelon continuous cultivation area, the problem of continuous cropping obstacle has also emerged. Fusarium wilt is one of the most serious diseases of watermelon, watermelon yield reduced 15%~85% by soil-borne diseases. The solutions need to appear in the modern agricultural production urgently. It is found that the use of exogenous substances and crop root exudates can alleviate continuous cropping obstacle and disease effectively, but the mechanism remains were unknowned now.The main aim of this study was to investigate the effects of hexadecanoic acid on watermelon growth and microbial of continuous cropping soil and Fusarium oxysporum. Watermelon growth, soil microbial communities and soil chemical properties were studied by conventional chemical method, PCR-DGGE, real-time PCR and other methods. The experiment was carried by pot experiment with 5 years of continuous cropping of watermelon soil in greenhouse. Main results of this paper were as following:(1) Hexadecanoic acid at low concentrations(0.25-1 mmol/kg) increased total root length, root surface area and root volume of watermelon, increased plant height, stem diameter and fresh weight and dry weight of watermelon, increased root activity, chlorophyll content and yield of watermelon. The treatment with 1 mmol/kg of hexadecanoic acid was the highest yield. High concentration of palmitic acid(4 mmol/kg) significantly inhibited the growth of watermelon.(2) Hexadecanoic acid can prevent Fusarium wilt effectively, different concentrations of hexadecanoic acid(0.25-4 mmol/kg) the incidence and disease index of watermelon wilt disease treatment was lower than that of the control treatment, Fusarium wilt disease incidence and disease index was the lowest at 1 mmol/kg.(3) At last stage(60d), low concentration of hexadecanoic acid(0.25-1 mmol/kg) significantly increased the soil available phosphorus content, high concentration of hexadecanoic acid(4 mmol/kg) significantly decreased the content of available phosphorus in soil; increased soil organic matter content. The soil EC value with the overall growth of watermelon increased at first and then decreased, Watermelon at later stage, with the increasing concentration of hexadecanoic acid, the soil p H was increased at first and then decreased. 1 mmol/kg soil p H was the highest.(4) With hexadecanoic acid concentration increased, the amount of soil bacteria and fungi were increased first and then decreased. At the late in the growth of watermelon, bacterial colonies and Fusarium oxysporum strains accounted for the highest percentage of fungi was higher than control at 0.25 mmol/kg, Fusarium oxysporum colony number was lowest at 4 mmol/kg.(5) Soil bacteria, fungi and watermelon specialized type of Fusarium oxysporum community size increasing. Bacteria and fungi copy number is higher than that of the control and other treatments at 1 mmol/kg hexadecanoic acid, Fusarium in copy number of the highest at 0.5 mmol/kg, it was higher than the control and other treatments significantly, bacteria, fungi and Fusarium oxysporum copy number was the lowest, significantly lower than the control at 4 mmol/kg hexadecanoic acid.(6) Bacterial and fungal bands, evenness index and Shannon-Wiener index was significantly higher than the control and other treatments at 1 mmol/kg. Bacterial bands, evenness index and Shannon-Wiener index is higher than control at high concentration of hexadecanoic acid(4 mmol/kg), fungal bands, evenness index and Shannon-Wiener index were lower than the control at 4 mmol/kg.(7) Different concentrations of hexadecanoic acid were significantly suppressed Fusarium oxysporum mycelial growth, 2 mmol/L hexadecanoic acid inhibition max. With the increasing of hexadecanoic acid concentrations, Fusarium oxysporum spore germination, sporulation could be inhibited.In summary, the concentrations of hexadecanoic acid were increased resistance to fusarium wilt of watermelon,and its best fruit weight in 1 mmol/kg. The administration of exogenous hexadecanoic acid can significantly promote the watermelon plant growth, improve watermelon fruit weight, maintain relatively higher soil microbial community diversities, reduced the number of Fusarium, prevent and control of watermelon wilt happen effectively.