Study On The Screening And The Main Biocontrol Mechanism Of Trichoderma Spp. On F. Oxysporum. F. Sp Cucumerium

In this paper,166 strains of Trichoderma spp. collected from East China were dually cultured with Fusarium oxysporum.f. sp.cucumerium which is pathogenic on cucumber,10 strains of Trichoderma spp. showing higher inhibitory ability than others, the antagonistic effect reach up to 60%, in which FZ22 get the highest inhibition rate, up to 79.04%. In the pot test against cucumber Fusarium wilt, FZ22 also demonstrated good bio-control ability, the control efficiency is up to 87.5%. FZ22 was identified by morphological and molecular methods. Result demonstrated that the strain belong to Trichoderma erinaceum Bissett.The method of screening Trichoderma spp. which is antagonistic to cucumber Fusarium wilt was improved. The comparative study was made of confront culture, pathogen survival measurement after antagonistic microbe treatment, degradation of pathogen mycelium by secrets from biocontrol microbe, seed germination recovery after inhibiting pathogen infection by biocontrol microbe and the screening of biocontrol microbe on host seedling in the presence of pathogen in attempt to establish an high-throughput screening method of biocontrol Trichoderma strains against Fusarium oxysporum in cucumber. Results suggested that much difference was found in the final rank of Trichoderma strains based on antagonistic evaluation with each of methods. However, the method based on pathogen survival measurement after Trichoderma treatment showed basically a consistent result with that from their screening on host seedlings, thus the former method could be recommended as an useful approach to make preliminary screening of bio-control Trichoderma strains.The study of Trichoderma FZ22 bio-control mechanisms shows that competition and mycoparasitism were the important mechanisms of FZ22 against pathogenic fungi. Trichoderma erinaceum can grow faster than pathogen, with space and nutrition competitive advantage. Microscopic observation demonstrated that FZ22 can attached to and wrapped in cucumber Fusarium, and eventually broken the mycelium of pathogen. The Trichoderma FZ22 generation of cell wall-degrading enzymes(CWDES) activities were tested on the background of different culture medium, media that contained Fusarium oxysporum exhibited much higher CWDE activities than media that did not contain Fusarium oxysporum. At 96h chitinase activity reached its peak, the value of peak activity is 22.6U/mg.β-1,3-glucanase activity started from the 72h has been showing a rising trend.The study of defense enzymes changes secreted by host plant cucumber was determined after inoculation at different times. Inoculation with Trichoderma FZ22 followed by Fusarium oxysporum was able to increase the activities of phenylalanine ammonia-lysae(PAL), peroxidase(POD), superoxide dismutase(SOD), prophenyloxidase(PPO). And all these defense enzymes have the same trend, which get a peak of activity at the 7th day. From the growth rate of enzymes activities, we can see the rapid rise for the first 5 days to 7 days. Meanwhile, the electrical conductivity of the host plant reflects the bio-control advantage of inoculation with Trichoderma FZ22 followed by Fusarium oxysporum.