Search

Objective: To evaluate the potential of Trichoderma longibrachiatum spore suspension against Heterodera avenae., Methods: The parasitic and lethal effects of T. longibrachiatum spore suspension against the cysts of H. avenae were studied in vitro and observed under microscope., Results: Microscopic observation showed that the spore suspension of T. longibrachiatum parasitized on the cyst surface, germinated a large number of hyphae, and grew on the surface of the cyst at the initial stage. Later, the cysts were completely surrounded by dense mycelium, and the contents of digestion in cysts was lysed, even some cysts produced vacuoles, and some were split up and finally the cyst was dissolved by the metabolite of T. longibrachiatum. In vitro studies showed that high concentrations of T. longibrachiatum spores had strong parasitic and lethal effects on the cysts of H. avenae, and the probable mechanism of parasitic and lethal effects of T. longibrachiatum against H. avenae were mainly by inducing and increasing chitinase, glucanase and caseinase activity. The cysts were parasitized by 93.3% at 18 days, the hatching of cysts were inhibited by 93.6% at 10 days when treated with the concentrations (1.5 x 10(8) CFU/mL) of T. longibrachiatum., Conclusion: Trichoderma longibrachiatum had strong parasitic and lethal effects on the cysts of H. avenae, and has the potential as a new biocontrol agent.

The lethal effect of the conidia suspension of Trichoderma longibrachiatum against second stage juveniles of Heterodera avenae was observed under microscopic conditions and studied in vitro to preliminarily determine the potential and mechanism of the conidia suspension of T. longibrachiatum against H. avenae. Microscopic observation results showed that the conidia suspension of T. longibrachiatum adhered to or parasitized on the surface of second stage juveniles, even some parasitized nematodes were deformed at the initial stage. Later, the second stage juveniles were wrapped and the integuments were penetrated by a large number of hyphae germinated from the conidia suspension of T. longibrachiatum. Even the body of dead second stage juveniles was completely lysed. In vitro studies showed that different concentrations (1.5 x 10(5)-1.5 x 10(7) cfu x mL(-1)) of T. longibrachiatum (conidia suspension) had strong lethal and parasitic effects on the second stage juveniles of H. avenae, and significant differences existed among the treatments with different concentrations of T. longibrachiatum. In addition, the lethal and parasitic effects increased with increasing the T. longibrachiatum concentration. The mortality and corrected mortality of the second stage juveniles treated with the concentrations of 1.5 x 10(7) cfu x mL(-1) were 91.3% and 90.4% after 72 hours, and the second stage juveniles were parasitized by 88.7% after 14 days. Therefore, the conidia suspension of T. longibrachiatum had a great lethal effect on H. avenae, and the strain could be considered as a potential bio-control agent against H. avenae.

A laboratory experiment was conducted to study the parasitic and lethal effects of Trichoderma longibrachiatum conidia suspension on Heterodera avenae cysts. Different concentrations (1.5 x 10(5)-1.5 x 10(7) cfu x mL(-1)) of T. longibrachiatum conidia suspension had strong parasitic and lethal effects on H. avenae cysts, and the effects differed significantly among the different concentrations. When treated with the T. longibrachiatum conidia suspension at a concentration of 1.5 x 10(7) cfu x mL(-1), 96.7% of the H. avenae cysts were parasitized by the conidia at the 18th day, and the hatching rate of the cysts was inhibited by 91.2% at the 22nd day. The microscopic observation showed that at the initial parasitic stage, T. longibrachiatum conidia suspension adhered or parasitized on the cyst surface, germinated a large number of hyphae, and grew on the cyst surface, making the development of cyst embryo stopped and the contents in cysts flocculated, and even, some cysts started to deform, and small dark brown vacuoles formed on the cyst surface. At the later parasitic stage, the cysts were penetrated by dense mycelium, cysts were broken, their contents exosmosed, and the mycelium on the integument of some cysts produced conidiophores, on which, conidium were adhered or parasitized. It was considered that T. longibrachiatum could be used as a potential high-efficient bioagent to control the occurrence and damage of H. avenae.

Objective: To understand the bacterial diversity isolated from the cysts of Heterodera glycines in the soybean field in Heilongjiang Province., Methods: Bacteria were isolated from cysts on nutrient agar plates using dilution plate method and further identified by phylogenetic analysis based on 16S rDNA gene sequences., Results: Totally 90 bacteria strains with different colony morphology were selected on nutrient agar plate and their phylogenetic features were analyzed based on the partial 16S rDNA sequences. In total 7 genera and 22 species were identified, including 46 strains in Gammaproteobacteria (51.1%), 32 in Firmicutes (35.6%), 10 in Betaproteobacteria (11.1%), and 2 in Alphaproteobacteria (2.2%). The dominant bacteria species were Pseudomonas and Bacillus., Conclusion: There was abundant species diversity of bacteria isolated from cysts Heterodera glycines in Heilongjiang, and these bacteria may play a physical and ecological roles in nematodes.

Twenty actinomycetes were isolated from root-knot nematode eggs and females collected from 11 plant root samples infested by Meloidogyne spp.. The isolates were assigned to the genera Streptomyces, Nocardia and Pseudonocardia respectively, based on analysis of morphological characteristics, cell-wall DAPs and 16S rRNA gene sequences. 80% of them were streptomycetes. Biocontrol potential of the isolates against Meloidogyne hapla was evaluated in liquid culture in vitro. The average percentages of egg parasitism, egg hatching, and juvenile mortality were 54.1, 40.4 and 26.2, respectively. Three Streptomyces strains and one Nocardia strain with high pathogenicity in vitro were selected to determine their ability to reduce tomato root galls in greenhouse. The results demonstrated good biocontrol efficacy (31.4%-56.4%) of the strains.