| Shenqinmycin is a novel antibiotic with the effective component phenazine-1-carboxylic acid originated from microorganisms. It is extracted from secondary metabolism substance of false cell strains M18 (Pseudomonas sp. M18) by Pro.Xu of Shanghai Jiaotong University. This fungicide was demonstrated to have activity against Xanthomonas oryzae pv. oryzae and Sclerotinia sclerotiorum, the compound had potential efficacy in controlling rice bacterial leaf blight and sclerotinia stem rot of oilseed rapes.The toxicity of shenqinmycin against 14 species of important agricultural pathogens was studied. The results showed that shenqinmycin strongly inhibited the growth of X. oryzae pv. oryzae with the EC50 value of 0.654μg/ml. and the relative virulence was 45.88 compared with streptomycin. At the same time.shenqinmycin was highly efficient against X. oryzae pv. oryzicola, S. Sclerotiorum and Botrytis cinerea. Their EC50 values in inhibiting growth were 3.335μg/ml,3.123μg/ml and 4.663μg/ml, respectively. However, it appeared much lower activity against other nine tested pathogenic fungi and bacteria. There was no cross-resistance between shenqinmycin and common used fungicides, such as carbendazim in B. cinerea.Sixty-one isolates of X. oryzae pv. oryzae were isolated from rice samples from Jiangsu. Anhui, Yunnan Province, where shenqinmycin had never been used before. The sensitivities to shenqinmycin were determined by the method of turbidity method. The results showed that the sensitivity of wild-type population in the nature against shenqinmycin exhibited a certain extend diversity and the EC50 values of the compound inhibiting growth of X. oryzae pv. oryzae ranged from 0.013 to 0.336μg/ml with the mean value of 0.110±0.006μg/ml The value of MIC was<12.5μg/ml. It showed that shenqinmycin strongly inhibited mycelia growth of X. oryzae pv. oryzae. Shenqinmycin had significant protective effect against rice bacterial leaf blight. the control efficacy became higher with the concentration increasing. When the concentration was 200μg/ml, its efficacy in controlling to rice bacterial leaf blight was 78.91%.24 h after bacteria treatment, the efficacy of shenqinmycin in controlling rice bacterial leaf blight was poorer. although the control effect was higher with concentration increasing compared to the increment of the protective effect. and its curative activity was significantly lower. Therefore, the preliminary work indicated that shenqinmycin had better protective activity, than that of curative activity against rice bacterial leaf blight.Shenqinmycin exhibited high inhibitory activity against X. oryzae pv. oryzicola, with the average EC50 of 3.630±0.401μg/ml, greater than that of X. oryzae pv. oryzae(0.110±0.006μg/ml) by about 33 times. The field experiment showed that the protective and curative activity of shenqinmycin in controlling rice bacterial leaf streak disease was higher, with the concentration increasing, and the efficacy of 300 g a.i./hm2 shenqinmycinin controlling the disease was 48.96%. Due to the difference of activity against these two kinds of pathogenic bacteria. it was still needed to test efficacy in controlling the rice bacterial leaf blight in the field.The translocation experiment of shenqinmycin to rice leaf showed that the pesticide could translocate upward in a leaf, but not to the bottom.In laboratory, we obtained totally 24 resistant mutants derived from wild-type isolates with a frequency between 5.3×10-8～7.9×10-8. Only two of them were pathogenic. Compared with the virulence of the original strains, they had no significant difference. Their EC50 values were 1.215μg/ml and 1.304μg/ml, respectively. As it had a low resistance frequency in inducing X. oryzae pv. oryzae and most of the resistant mutants had lost their pathogenicity, shenqinmycin might be at low risk of resistance.Moreover, the sensitivity of S. sclerotiorum isolates to shenqinmycin was tested. The results showed that the EC50 value of shenqinmycin against mycelia growth of 51 tested S. sclerotiorum isolates was 3.305±0.775μg/ml in average. There was no cross-resistance between shenqinmycin and common used fungicides, such as carbendazim and dimethachlon in S. sclerotiorum. The control efficacy of 200μg/ml shenqinmycin against sclerotinia stem rot on the detached leaves of oilseed rape was 67.08% with excellent protective activity against this disease. The results of field trial showed that the control efficacy of 200μg/ml shenqinmycin against sclerotinia stem rot of oilseed rapes was 83.29%. which was better than that of the reference fungicide iprodione. Therefore. the authors suggested that shenqinmycin could be used for the control of sclerotinia stem rot of oilseed rape and the management of carbendazim resistance in the field. |
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