Combinative Application Of Dazomet And Paecilomyces Lilacinus Against Tomato Root-knot Nematode

The increasing of soilborne diseases has caused enormous losses in protected vegetable productionin China in recent years. Root-knot nematode is one of the most serious diseases and has become anobstacle of development of vegetable industry. Soil fumigation and biological control are two efficientmeasures frequently used against the disease. In this study, the low-toxic fumigant Dazomet was appliedin combination with the biocontrol agent Paecilomyces lilacinus YES to combat Meloidogyne incognitaon tomato. The mechanism of integrated management of both practices was investigated and the controlefficiency in greenhouse was evaluated. This research provides theoretical basis for effective control ofroot-knot nematode and efficient application of biocontrol agents.The results demonstrated that the eggs of root-knot nematode were extremely sensitive to Dazomet.When dealt with 5 mg/kg of Dazomet, the rate of hatched juveniles was 2.0%, accounting for 4.7% ofthe blank control. The isolate YES showed strong parasitic capacity to nematode eggs. The percentageof eggs infected reached 55.5% in 5 days when immersed in 6.5×104 spores/ml fungal suspension, andincreased to 84.0% when the concentration of YES increased tenfold. Preprocessing with fumigantsignificantly enhanced the egg-parasitic ability of P. lilacinus; the parasitic rates of YES with lowconcentration on nematode eggs fumigated with 5-25 mg/kg of Dazomet increased to 77.9%~85.6%(P<0.05). The synergistic effect was the strongest when exposed to 7.5 mg/kg of Dazomet, whichincreased by 54.2% in 132 h compared to YES applied alone. Mortality of second-stage juveniles ofroot-knot nematode increased with the increasing of fumigant and YES fermentation filtrate, and thetolerance of juveniles fumigated to fungal filtrate decreased significantly(P?0.05). When treated with10 and 20 mg/kg of Dazomet followed by 10-time diluted YES filtrate for 3 days, the mortalities ofnematodes reached 24.8% and 95.0%, respectively, which were significantly higher than those offumigant and nematophagous fungus used alone(P<0.01). Both Dazomet and P. lilacinus reduced thepathogenicity of juveniles to tomato roots remarkably. When Dazomet and YES used alone, thenumbers of juveniles penetrating into young roots decreased by 90.0% and 48.7%, respectively, 4 daysafter inoculation, and the knots reduced by 71.9% and 31.4% in 45 days compared to the control. Therewas no juvenile detected in the roots in the combined use of the two practices in 4 days and the numberof knots reduced by 99.7% compared to the control.In order to clarify the combinative effect of fumigant and biocontrol agent on tomato root-knotnematode, Dazomet and P. lilacinus YES was applied successively in protected greenhouse. When 35g/m2 of Dazomet was used, the numbers of nematodes in soil and on root decreased by 89.1% and91.6% respectively compared to the control and the control efficiency reached 85.5% in 24 week aftertransplanting. For P. lilacinus, the control efficacies were 45.0%~65.0% when applied in holes atconcentrations of 107~108 CFU/g. However, the effect of the nematophagous fungus was only 12.5% ata high density of 674 juveniles/100 g soil. But plant growth and tomato yield were significantlyimproved. After soil fumigation with Dazomet, followed by hole application of P. lilacinus agent, thecontrol efficacies enhanced by 14.1% and 21.8% in two and five months, respectively, compared toDazomet used alone, enhanced by 14.3 and 4.1 times compared to the fungal agent used alone, andtomato yield increased by 22.1%, 9.5% and 2.4% compared to the blank control, Dazomet and YEStreatments. The number of nematode was the least in the whole growing season, which was significantlydifferent from the control, while the population of P. lilacinus in rhizosphere soil was greater than thatof the single biocontrol treatment. The results demonstrated that the integrated use of Dazomet and P.lilacinus could inhibit nematode density, enhance control efficacy to root-knot nematode effectively, andpromote plant growth and yield.