Preliminary Study On Pesticidal Activities Of Benzothiazole And Other Microbial Volatile Organic Compounds

Plant diseases, pests and weeds are important factors that influence the plant health, crop production, quality and ecosystem stability. Microbial volatile organic compounds (mVOCs) play significant roles in the control of them. Based on the preliminary research of our laboratory, we selected three compounds (benzothiazole, 1-octen-3-ol, citronellol) with higher activity and better applied potential as investigated subject, their bioactivities against several pathogenic fungi, Oomycete, Stored grain insect Tribolium castaneum, Bemisia tabaci Genn were studied. Besides, the determination of toxic action modes, symptom of insects and biocontrol application in greenhouse was also carried out. The findings of the present study suggested the antifungal, insecticidal and herbicidal properties of the components contained in volatiles. These agents or even their derivatives may have a potential to be used as fungicide, insecticide as well as herbicide.Antifungal bioassays in sealed plates revealed that the three compounds strongly inhibited the mycelia growth of the 9 pathogens (Sclerotinia sclerrotium, Botrytis cinerea, Fusarium oxysporum, Rhizoctonia solani, Phytophthora capsici, Colletotrichum capsici, Phytophoria melonis, Alternaria brassicae, Pestalotiopsis photiniae) with wide host plants at a low treatment dosage. Relatively speaking, of the three compounds, benzothiazole displayed high levels of antifungal activity, 1-octen-3-ol was a little lower and the least toxic compound was citronellol. All these results demonstrated the potential of mVOCs in the control of soilborne pathogens.The determination of toxic action modes in sealed plates indicated that, these compounds had obvious inhibition activity against the mycelium growth, spore germination, pigment production, sclerotia germination and reproduction, respiration and conductivity of mycelium. The mycelium growth of S. sclerotirum exposed to the compounds for 7 d was completely inhibited, and the formed mycelium was freakish-contorted, swelled, protoplasm agglomerated, branched more frequently at the end and the flexibility was decreased. After exposure to these compounds for 24 h, germination of most spores became decreased (Inhibition percentage 70%-80%) and the elongation of germ tube was inhibited. An unexpected phenomenon was found that these compounds showed inhibition on the production of pigment in test pathogenic fungi, an interesting phenomenon was that citronellol could completely inhibit the pigment formation of F. oxysporum. Compared with controls, the germination of sclerotia in treatment plates were delayed for different times and the sclerotia that reproduced were oddly shaped, not plump and very spongy when touched and distributed unevenly in the plates. Besides, they also could obviously inhibit the respiration of mycelia and increase the permeability of plasma membrane.The fumigation effect of benzothiazole, 1-octen-3-ol, citronellol is very effective against stored grain insect Tribolium castaneum, LC50 were 16.76 mg L-1 and 3.50 mg L-1, the toxic symptom of the compounds was characterized by a definite sequence of events, firstly showed much more mitigative and then started with excitation, convulsion, paralysis, and death. The compounds even showed intense fumigation effect against B. tabaci, and obviously affected their respiration.Besides, the results of herbicidal assays showed that the tested compounds had good effects on the seed germination and seedling growth of Amaranthus retroflexus, Echinochloa crusgalli and Chenopodium album.In greenhouse, applied the compounds directly as fumigation, these volatiles could significantly inhibit the disease severity of powdery mildew and B. tabaci on the fumigating seedlings. Of the three compounds, 1-octen-3-ol and benzothiazole had relatively high activity whereas effect of the citronellol was relatively low. Furthermore, under the appropriate dosage, a slightly growth promotion of cucumber seedlings was shown. Obvious symptoms that harmful to the seedlings appeared when the dosage was increased.