| The resistance of X oryzae pv. oryzae to saikuzuo was monitored in viva and in vitro. The results showed that the resistant isolates of X oryzae were found in viva, and the resistant frequency in 1999 was higher than that in 1997 and in 1998 in Anhui. But the rice leaf blight was not found in 1999 in Jiangsu, and the resistantIfrequency in 1998 was lower than that in 1997. The resistant mutant was not acquiredin vitro.There was no significant difference between the resistant mutants (R) and the sensitive isolates (S) of X oryzae to saikuzuo in the growth rate, pathogenicity and the activities of extracellular enzymes. But the extracellular products released from mutant were more serious damage to the detached leaf pieces of rice than that of wide-type strain , and the level of lipid peroxidation induced by mutant was higher than that of sensitives. EPS could decrease the sensitivity of X oryzae to saikuzuo, and the resistant of X oryzae was closely related with its extracellular products. After 10 cycles of subculture on the bactericide-free medium, the resistance level and pathogenic of resistant decreased slightly, some of mutants lost their pathogenicity . It was also found that EPS of saikuzuo-resistant and sensitive was made of the same monose, but physical and chemical character of EPS were different between mutant and sensitive ones.The results of action mode of saikuzuo against rice leaf blight showed that, in vitro, saikuzuo bactericide had direct effect on inhibition growth of X oryzae pv. oryzue. Saikuzuo was added at various incubated periods, the inhibition activity was different against Xoryzcw. In viva, saikuzuo expressed its protective and curative efficacy on controlling rice leaf blight caused by X oryzae pv. oryzae, and it had effect72on induction of rice resistance to X oryzae. Lipid peroxidation and superoxide anionin creased in the leaves treated with the bactericide.The inhibition activities of three different proportion mixtures of TH-88 and saikuzuo against X oryzae were detected by turbidity in vitro. The results showed that additive action was obtained in three mixtures bectericide. In field plot test, the results showed that the controlling effect of 20% mixture of TH-88 and saikuzuo EC diluted by 800 times against rice leaf blight was better than that of 20% saikuzuo WP diluted by 500 times, and the weight per 1000 rice grains and production were higher also. Therefore, in fact, the mixture of TH-88 and saikuzuo EC could be used to control rice leaf blight at the disease early stage and manage the resistance of X. oryzae to saikuzuo. |
