| Root-knot nematodes(Meloidogyne spp.) are a group of important pathogens on various crops, causing the severe damage to the crop production. Especially with the increasing of cultivated area of greenhouse vegetables, root-knot nematodes have become the biggest obstacle to the production of greenhouse vegetables. In this background, the biological control for this disease has drawn more and more attention recently.In this study, we isolated 537 fungal strains from females and eggs of Meloidogyne spp. collected from plant roots and infested soil in Jiangsu, China, and examined their in vitro protease productions and chitinase activities. Then we selected 20 strains, each with a protease production higher than 2.00 (protease production was measured as the ratio of diameters of the zone of clearing to that of the colony) and a chitinase activity higher than 0.2 U/min ml. For these strains, we examined their egg parasitic rates, mortality rates of stage 2 juvenile (J2), egg hatching rates and evaluated their biocontrol efficacies under greenhouse conditions. The biocontrol efficacies of these 20 potential biocontrol fungal strains ranged from 29.0%to 58.4%.The actual biocontrol efficacy against Meloidogyne root-knot was highly correlated with the in vitro protease production (r= 0.82), chitinase activity (r= 0.80), and the mortality of J2 (r= 0.76), but poorly correlated with the egg parasitic rate (r= 0.51) and the egg hatch rate (r= 0.52).Based on these results, we suggested that in vitro protease productions or chitinase activities of the fungal strains could be an applicable indicator for assessing biocontrol efficacy against nematodes.We screened out three biocontrol strains of Paecilomyces lilacinus XT18, XCS46 and Pochonia chlamydosporia XT124 and determined their biocontrol efficacy against root-knot disease, the yield increasement and the effect on diversity of rizosphere in the field trial in Suqian of Jiangsu Province. In 2007, the results indicated that biocontrol efficacies of XT18, XCS46 and XT12 were 60.7%,51.5%, and 48.1% respectively. And the yield increasements of these three strains were 62.0%,43.1%, and 40.4%, respectively. In 2008, the results showed that biocontrol efficacies of XT18, XCS46 and XT124 were 72.1%,54.5% and 51.9%, respectively. Either the biocontrol efficiency or the yield increasement of them was better than that of abamectin in the two years. The results of the two years also showed that after 40 d of transplanting the tomatoes (Secend treated with antagonist spore suspensions of XT18、XCS46 and XT124)), they significantly affected the micro-ecological of rizosphere after treatment and became the dominant species in all the habitats, and the number of each strain was above 105 CFU/g sampled soils by detecting the number of isolates on plates, and they could reduce the quantity of other fungi, bacteria and actinomycetes compared with the control.In order to investigate whether the antioxidant enzymes were associated with the biocontrol mechanisms in Paecilomyces lilacinus XT18, XCS46 and Pochonia chlamydosporia XT124, the roots of the tomatoes were treated with the spore suspensions of XT18, XCS46 and XT124, and 3 d after transplanting, the tomatoes were inoculated with M. incognita, the activities of Phenylalanine Ammonia-Lyase (PAL) polyphenoloxidase (PPO), Peroxidase (POD) and Superoxide Dismutase (SOD) were measured 0,1,2,3,4,5,6,7 d after inoculation. The results showed that XT18, XCS46 and XT124 significantly increased the activities of PAL, PPO, POD and SOD, when compared to the control 1 (the tomatoes were only inoculated with M. incognita) and control 2 (the roots of the tomatoes were only treated with sterile water). The highest activites of these four enzymes appeared 4,5,2, and 3 d after inoculation, respectively. These results indicated that the increased activities of antioxidant enzymes might be correlated with the induced resistance in the tomatoes to M. incognita.The growth characteristics of Paecilomyces lilacinus XT18(mycelial growth and spore production) under different media, temperatures, shaker’s eccentricity were studied. The results showed that different cultured conditions would affect the growth of XT 18 and the activity of its supernatant which could cause death to the J2 of M. incognita. The dry weights of the mycelia were 672.5 mg/100 ml and 635.4 mg/100 ml, when cultured in the maize and potato liquid media for 8 d, respectively. The spore productions were higher in potato and Czapek liquid media and were 34.8×107spores/ml and 34.6x107spores/ml, respectively. And the activity of the supernatant in Czapek liquid media was highest against the J2 of M. incognita.The results also showed that 25℃was the most suitable temperature for the mycelial growth and spore production of XT 18 and when cultured under 29℃, the supernatant exhibited greatest activity against the M.incognita isolate J2. The best shaker’s eccentricity for the mycelial growth and spore production of XT 18 was 110 rpm, and the mortility was 51.4% when the J2 of M. incognita was treated with the 10 d-cultured supernatant under this eccentricity. |
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