Nematocidal Effect of 1,2,4-triazole Derivatives Against Bursaphelenchus xylophilus

Background and Objective: Pine wood nematode, Bursaphelenchus xylophilus, infects pine trees and causes the pine wilt disease. This disease is one of the major threats to pine trees, thus causing global concern. The present study aimed to evaluate the potential nematocidal effect of some 1,2,4-triazole derivatives and to analyze their structure-activity relationships. Materials and Methods: Eight previously synthesized 1,2,4-triazole derivatives were selected for this study and designated as compounds 1 through 8. The nematocidal effects of 6 different concentrations (50, 100, 200, 300, 400 and 500 ?M) of these compounds were tested against Bursaphelenchus xylophilus. Results: At concentrations of 50-500 ?M and with 6 h of exposure, the all of the test compounds killed nematodes in a concentration-dependent manner. Among these compounds, compound 1 exhibited the most potent nematocidal activity at all tested concentrations and exhibited the lowest LD50. The highest mortality rate of 100% was only observed by compound 1, followed by compound 2 with 85% mortality rate after exposure to 500 ?M for 6 h. Under the same conditions, the lowest mortality rate of 33% was obtained by compound 4. The LD50 of 50 ?M was recorded for compound 1, followed by compound 2 with 70 ?M. The LD50 value of compound 4 was at least 10 times higher than that of compound 1. Analysis of their structure-activity relationships suggested that the highest nematocidal activity was due to the presence of a primary amine on the substituted phenyl ring. Conclusion: Monosubstituted forms of the phenyl ring displayed much better nematocidal activity compared to unsubstituted or di-substituted forms. Compound 1 showed the highest nematocidal activity of all tested compounds, a finding that corresponded to the presence of a primary amine on the phenyl ring. These results demonstrated for the first time, that compounds containing a 1,2,4-triazole ring could be of importance as nematocidal drugs for combatting the pine wilt disease, the potency of which is influenced by the specific substitution pattern on the phenyl ring.