Antagonistic Activities of Volatiles from Four Strains of Bacillus spp. and Paenibacillus spp. Against Soil-Borne Plant Pathogens

The four effective antagonistic Bacillus strains, isolated from the rhizosphere soil of cucumber in a greenhouse, produced antifungal volatiles. These volatiles strongly inhibited the growth of the most tested pathogenic fungi with wide host plants, induced the mycelial morphological abnormalities, and decreased the sclerotoid production of Sclerotinia sclerotiorum in sealed plates. Spores of Botrytis cinerea exposed to these volatiles for 24-48 h in cavity slides cracked and the sporaceous inclusion became brown and effused to the suspension. An interesting phenomenon observed was that all the bacterial volatiles exhibited intense inhibitory activities against the pigment formation of tested pathogenic fungi, including Ascochyta citrullina, Alternaria solani, Alternaria brassicae, and so on. Interactions mediated by microbial volatiles could be widespread in soils, and volatiles may play an important role in reducing disease levels. A phylogenetic analysis based on 16S rDNA sequence placed the four bacteria in three species Paenibacillus polymyxa （BMP-11）, Bacillus subtilis （BL02）, and Bacillus pumilus （BSH-4 and ZB 13）. Through headspace sampling and GC-MS analysis, a rich profile was found from B. subtilis and overlapping volatile patterns could be found among the different species. Studies are under the way to find the possible action mechanisms and to seek the effective application of bacterial volatiles in greenhouse.

Antifungal,Insecticidal and Herbicidal Properties of Volatile Components from Paenibacillus polymyxa Strain BMP-11

The volatiles produced by Paenibacillus polymyxa strain BMP-11 which was isolated from the rhizosphere soil of cucumber in a greenhouse were analyzed by SPME-GC-MS.Based on the preliminary test,three kinds of purchased commercial products 1-octen-3-ol,benzothiazole and citronellol were chosen to give further assessment of their bioactivity.Antifungal bioassays in sealed dishes revealed that those three compounds strongly inhibited the mycelia growth of the eight pathogens at a low treatment dosage and induced the mycelial morphological abnormalities.During the experiment,we even found that citronellol completely prevented the pigment production of the tested fungus,Fusarium oxysporum,however,1-octen-3-ol and benzothiazole had slight effect.The germination was inhibited to different degrees when spores of Botrytis cinerea exposed to these compounds for 24 h in water agar plate.Furthermore,fumigation results showed that 1-octen-3-ol and benzothiazole had strong toxicity against Tribolium castaneum,LC50 was 16.76 and 3.50 mg L-1,respectively.The fumigation activity was also found similar to the positive control,1,3-dichloropropene （LC50 =10.13 mg L-1）.Results of herbicidal assays showed that tested compounds had inhibitory effects on the seed germination and seedling growth of Amaranthus retroflexus,Echinochloa crusgalli and Chenopodium album.Findings of the present study suggested that the antifungal,insecticidal and herbicidal properties of the components were contained in volatiles.These agents or even their derivatives may have a potential to be used as fungicide,insecticide as well as herbicide.

Effects of Tebufenozide on the Biological Characteristics of Beet Armyworm (Spodoptera exigua Hübner) and Its Resistance Selection

In this article, the selection of tebufenozide to beet armyworm （Spodoptera exigua Htibner） was studied by the treatments to alternative generations＇ 3rd-instar larvae with LC50 dose and to continuous generations＇ larvae with LC10 dose; the effects of tebufenozide on the biological characteristics of current and subsequent generations were examined by the treatments to 3rd-instar larvae and egg pods in different concentrations. After treatments with LC50 dose till F11, the toxicity of tebufenozide to beet armyworm had no significant change, whereas the pupation rate, pupal weight, and fecundity were reduced markedly. After treatments with LC10 dose till Fl9, the beet armyworm only developed 3.52-fold resistance, and the main biological characteristics were nearly accordant in each generation. The livability was reduced 72 h later after treatments to 3rd-instar larvae, respectively in 2.5-40 μg mL^-1, and larval duration, pupation rate, and pupal weight changed considerably with the increase in concentrations. The fecundity, larval livability, larval weight and pupal weight of subsequent generations were reduced as the dose increased over 10 μg mL^-1. The hatching rate of egg pods did not differ with that of the controls obviously after treatment in 10-300 μg mL^-1. But the larval livability, larval weight and pupal weight were reduced when eggs were exposed to 50 μg mL^-1 dose or more. The results indicated that tebufenozide had low resistance risk to the current and subsequent generations of beet armyworm even if tebufenozide had significant effects on the biological characteristics of this insect.