Effects Of Several Chemical Pesticides For Controlling Soil-borne Diseases On Chlamydospores Of Trichoderma Spp

Trichoderma spp. is an important biocontrol fungus. Trichoderma chlamydospores are generatedunder adverse conditions as progagules, which are thick-walled asexual spores and can enhance stressresistance including desiccation resistance, soil fungistasis, and can survival for a long time, and hencechlamydospores are more advantageous in processing and storage of biocontrol agents. Effects ofchemical fungicides on the biocontrol functions of Trichoderma preparations are still unclear. In thisstudy, two Trichoderma strains,758and610were screened with competitive antagonism effects onseveral soil borne pathogenic fungi. The chlamydospores of strains were produced and the effect ofchemical fungicides on chlamydospore germination and mycelial growth of Trichoderma spp. werestudied. Effects of metham sodium sterilized soil on Trichoderma spp. and Fusarium oxysporum f. sp.cucumerinum (FOC) and controlling of cucumber Fusarium wilt by using chlamydospore preparation ofT. longibrachiatum758and pentachloronitrobenzene were also studied. The results were as follows:1. Screening and identification of Trichoderma spp. strainsTwo Trichoderma spp. strains758and610were screened for in vitro antagonism againstPhytophthora capsici Leonian, Fusarium oxysporum f. sp. Cucumerinum, Fusarium oxyporumf.sp.niveum, Alternaria solani, Rhizoctonia solani Kühn, Rhizoctonia cerealis.758was indentified to beT. longibrachiatum and610to be T. harzianum by sequence alignment.2. Preparation of chlamydospores of Trichoderma spp.Chlamydospores of T. harzianum610and T. longibrachiatum758were prepared by submergedfermentation process. The final concentration of chlamydospores was107-8cfu/mL.3. Effects of chemical fungicides on mycelial growth of Trichoderma spp.Seven commonly used chemicals fungicides for soil-borne deseases, carbendazim, tebuconazole,difenoconazole, thiram, carboxin, pentachloronitrobenzene and metalaxy, had different degrees ofinhibitory effects on growth of T. harzianum610and T. longibrachiatum758, the toxicity order ofseven chemical fungicides on mycelial growth of T. harzianum610by comparing the EC50values was：pentachloronitrobenzene<metalaxyl<carboxin<thiram<tebuconazole<difenoconazole<carbendazim.Pentachloronitrobenzene showed the weakest inhibitory effect on mycelial growth of610, EC50valuewas1266.00μg/mL; carbendazim showed the strongest inhibitory effect, EC50value was0.05μg/mL.As for T. longibrachiatum758, the toxicity order was: smetalaxyl<pentachloronitrobenzene <carboxin<thiram<carbendazim<difenoconazole<tebuconazole. Pentachloronitrobenzene and metalaxyl showedthe minimal inhibition, EC50value were1149.96μg/mL and1206.29μg/mL; tebuconazole showed thestrongest inhibitory effect, EC50value was0.32μg/mL.4. Effects of chemical fungicides on chlamydospore germination of Trichoderma spp.Seven chemical fungicides had different degrees of inhibitory effects on chlamydosporegermination of T. harzianum610and T. longibrachiatum758. The toxicity order of seven chemicalfungicides on chlamydospore germination of T. harzianum610by comparing the EC50values was: pentachloronitrobenzene<carboxin<metalaxyl<thiram<difenoconazole<tebuconazole<carbendazim.Pentachloronitrobenzene showed the weakest inhibition, EC50value was681.82μg/mL; carbendazimshowed the strongest inhibition, EC50value was1.64μg/mL. As for T. longibrachiatum758, thetoxicity order was: metalaxyl<thiram<carboxin<tebuconazole<difenoconazole<carbendazim. Metalaxylshowed the weakest inhibitory effect, EC50value was1108.61μg/mL; carbendazim showed thestrongest inhibitory effect, EC50value was0.62μg/mL.5. Effects of metham sodium sterilized soil on Trichoderma spp. and Fusarium oxysporum f. sp.cucumerinum (FOC)Metham sodium sterilized soil had no obvious inhibitory effects on chlamydospore germination ofT. longibrachiatum758, conidial germination of FOC and the mycelial growth of T. longibrachiatum758and FOC. But T. longibrachiatum758showed inhibitory effects on FOC when the two strainscoexist in soil.6. Control of cucumber Fusarium wilt by using chlamydospore preparation of T. longibrachiatum758and pentachloronitrobenzene.There were not obvious biocontrol effects of chlamydospore preparation of T. longibrachiatum758alone against cucumber Fusarium wilt. Application of chlamydospore preparation of T.longibrachiatum758would reduce the control effects of pentachloronitrobenzene on cucumberFusarium wilt. The cause needs further studies.