Screening Of New Benzothiazole-phosphite Derivates With Antifungal Activities And Preliminary Study On The Mechanism Of Action

Aminophosphonic derivates synthesized in this research center were assayed using the mycelial growth rate method. It was found that benzothiazole-phosphites (05145, 05147, 05148 and 04172) substituted by amido and aminophosphonate (05223) showed certain antifungal activities in vitro. The spectrum and extent of their antifungal activities were studied by means of bioassay, microscopy and biochemistry. Also, the mycelium dry weight and the changes of hyphal morphology, the mycelial soluble protein, reducing sugar, D-GlcNAc content and chitinase activities of Fusarium graminearum were investigated to supply references to develop new fungicides. The preliminary results are as follows.Four benzothiazole-phosphites had broad fungicidal spectrum, with 50% effective concentrations (EC＿(50)) ranged from 15.0 to 148.2 ug.mL^-1 against F. graminearum, F. oxysporum, T. cucumeris, P. oryzae, C. mandshuric and R. solani. Part of the hypha and ramification were observed shriveling and collapsing. After treatment with four benzothiazole-phosphites at 300 μg.mL^-1 within 12 h, the mycelial reducing sugar content declined obviously and chitinase activity increased significantly. But the soluble protein and D-GlcNAc content increased in the short time and decreased subsequently. It could be speculated that four compounds may interfere with the metabolism of carbohydrate, which resulted in the shortage of glucides inducing the expression of chitinase gene. The fresh chitin composed at the end of hypha was hydrolyzed by chitinase, which influenced the form of hyphal cell wall so as to inhibit the growth of plant pathogenic fungi.It was discovered that the EC50 of aminophosphonate 05223 against F. graminearum, F. oxysporum, T. cucumeris, R. solani, P. oryzae, C. mandshurica, P. infestans, S. sclerotiorum and B. cinerea ranged from 30 to 100 ug.mL^-1. After treatment, hypha became slimmed, fragile and ramified crookedly, and the space between hyphal branches was found shortened. With the increase of aminophosphonate concentration, the mycelium dry weight decreased significantly.