Action Mechanisms Of Validamycin A Controlling Rice Sheath Blight

Rice sheath blight is the first one in the three biggest agriculture diseases of China. It destroys the rice production heavily ever year. The pathogen of rice sheath blight is Rhizoctonia solani. Currently Validamycin A is mostly used in controlling the rice sheath light. ValidamycinA was found in 1970s. It is high effective, not poisonous and side-effective, with low environmental influence. It is product of Streptomyces hygroscopicus. Although Validamycin A controls the disease very well, but its action mechanisms is not known. This thesis is mainly about Validamycin A inducing resistance and its role in inhibiting cell wall degrading enzymes. Major results are as follows:First, the sensitivity of Rhizoctonia solani isolated in 2006 was compared with that of isolates collected in 1999 with a trend of sensitivity decreasing in isolates collected in 2006. Further studies showed this is not related cross resistance. The result of sensitivity comparison conducted on rice plants also showed a decreased sensitivity in isolates collected in 2006, but not as obvious as that of in vitro test. We did not find the strain with high resistance Validamycin A in this study. Fingerprinting analysis revealed that the rise of resistance is correlated to the genetic differentiation.Second, to examine the induced resistance in rice, three concentrations: 10μg/ml, 100μg/ml, 200μg/ml of Validamycin A were compared with water and BION controls.. It was found that treatment with 100μg/ml Validamycin A, the enzyme activity of PO and PAL changed greatly, reaching to its peak on the first day. The PO enzyme activity changed little in BION, but the PAL changed obviously. So we thought Validamycin A could induce rice resistance. But in the experiment in vivo, the function of induced resistance can not control rice sheath blight, so the induced resistance is not main action mechanism of the antibiotics.Third, Validamycin A was added into cellolase at the concentration of lug/ml, 10μg/ml, 100μg/ml with no Validamycin A as control. Results showed that the enzyme activity did not change obviously suggesting that Validamycin A can not inhibit cellolase activity.