The Preventive Effects Of Rhamnolipid Treatments On Fusarium Wilt Of Watermelon

In this study, we investigated the influence of rhamnolipids on the spore germination, mycelium growth, the structure of spores and the activity of chitinase and beta1,3-glucance enzyme through the methods of the PDA training and irrigation of watermelon root, and attempted to study the effect of different concentrations of rhamnolipid in preventing the disease incidence of watermelon and preliminary explored the mechanism of rhamnolipid in preventing the disease incidence of watermelon. The main research results were as follows:1The influence of rhamnolipid treatments on the spore germination and mycelium growth of fusarium wilt of watermelonThe concentrations of rhamnolipid were0.5g/L,1.0g/L,2.0g/L,5.0g/L of PDA medium, while PDA training fusarium oxysporum f.s p.niveum, having no rhamnolipid PDA medium was used as control. The results showed that rhamnolipid obviously inhibited the spore germination and mycelium growth of fusarium wilt. When the concentration was0.5g/L, the inhibition was the least, which increased gradually as the concentration increased, while with the concentration of5.0g/L, a complete inhibition of the growth of fusarium wilt was observed. Likewise, rhamnolipids also influenced number of spores. It was found that there was inverse relationship between rhamnolipid concentrations and number of spores. The numbers of spores were decreasing with the increasing concentrations.2The effect of rhamnolipid irrigation of watermelon root on watermelon fusarium wiltThe concentrations of rhamnolipid0.5g/L,1.0g/L,2.0g/L,5.0g/L, and equivalent water as control were used to irrigate watermelon root. The results indicated that rhamnolipid obviously inhibited the fusarium wilt of watermelon. When the concentration was0.5g/L, they presented a significant difference as compared to control. The higher concentrations showed the the lower rates of disease incidence. But very higher concentrations of rhamnolipid inhibited the growth of watermelon seedlings. Hence, keeping in view a few factors, the optimum concentration was1.0g/L.3The influence of rhamnolipid treaments on spores surface and the internal structure of fusarium oxysporiumThe fusarium oxysporium spore suspension with0.1g/L and0.5g/L of rhamnolipid, and clear water treatment as control, were observed under a microscope. We noted that the influence of rhamnolipid on spores’surface structure was not significant, but the internal structure was significant, and appeared like a bubble. As the concentration was getting higher, the devastating effect on internal spores’ structures was also increasing.4The influence of rhamnolipid on enzymes activities related to fusarium wilt resistance.This study proved that the rhamnolipid in the greenhouse environment can induce plant resistance to defend the watermelon blight. The chitinase and beta1,3-glucance enzyme activity determination showed that after48h of different concentrations of rhamnolipid treatments, two kinds of the enzyme were significantly increased. We found that four days after foliar spray treatments, the activity of chitinase and beta1,3-glucance enzyme presented a consistent increase, especially when the concentration of rhamnolipid was1.0g/L, the activities of beta1,3-glucance (63.04%) and chitinase (49.95%) were higher than the control. Hence it was concluded that rhamnolipid can effectively protect watermelon from fungal infection.