Analysis On Fosthiazate-resistnance Of Meloidogyne Incognita And Resistance Management Strategy

Root-knot nematodes Meloidogyne incognita(RKNs) developed resistance to fosthiazate to a certain extent after using fosthiazate in greenhouses for consecutive years. In this investigation, the organophosphorus nematicides resistance-related genes of AChE in resistant population of Meloidogyne incognita were cloned, resistance level and mechanism of M. incognita were revealed via RT-PCR, enzyme activity assay and RNAi technology, and resistance management strategy was preliminarily explored.Determination of protein content and specific activity of AChE by enzyme activity assay and coomassie brilliant blue G-250 staining found that the specific activity of AChE in susceptible population is significantly higher than that in resistant population. Determination of AChE susceptibility of resistant and susceptible population to fosthiazate showed that the AChE of resistant population is less sensitive. AChE genes(Mi-ace-1 and Mi-ace-2) of resistant population and susceptible population were cloned using RT-PCR. Multiple sequence alignment showed that different nucleotide acid which irregularly distributing in the sequence are 68 between Mi-ace-2 and Mi-ace-2a, and 18 in amino acid sequence. The Mi-ace-2 in resistant population was silenced using RNAi technology, and the susceptibility of resistant population to fosthiazate was improved after RNAi. Results implied that the Mi-ace-2 played an important role in nematicide fosthiazate resistance.Primary resistance management strategy focused on biological control and cultural control. The in vitro ovicidal and larvicidal activities of Syncephalastrum racemosum, Paecilomyces lilacinus and Bacillus cereus were tested on cucumber, and their combined effects against M. incognita were evaluated in pot and greenhouse experiments. The results showed that all the bioagents displayed nematicidal potential via their ovicidal and larvicidal action. The highest ovicidal activity was recorded for the combination of S. racemosum and P. lilacinus at a concentration of 50%, and the best larvicidal activity was observed in the S. racemosum treatment at a concentration of 50%. Application of S. racemosum combined with P. lilacinus significantly stimulated the root length, shoot length and plant weight of cucumber plants, and significantly fewer galls and nematodes were observed. Under the greenhouse conditions, the combination of S. racemosum and P. lilacinus not only decreased the nematode severity but also increased the cucumber yield compared to the untreated control. The results indicated that the combined use of S. racemosum and P. lilacinus represents a new biocontrol strategy against parasitic nematodes in protected agricultural areas. In the study of cultural control, four mechanical tillage technologies included shallow tillage, deep tillage, shallow tillage in combination with dazomet, and deep tillage in combination with dazomet were carried out to evaluate the effects on nematodes and micro minerals. The results showed all the four treatments significantly reduced the number of root-knot nematodes in the soil, improved the control efficacy, and increased the yield of watermelon. Among those treatments, deep tillage in combination with dazomet showed the best control efficacy and watermelon production, and increased the level of exchangeable magnesium and effective selenium. Comprehensive evaluation suggested that deep tillage in combination with dazomet was applicable to the areas where root-knot nematodes occurred severely, while the shallow tillage treatment was effective for the areas where the disease is not very serious. In this investigation, a new mode of controlling root-knot nematode was presented by deep tillage in combination with fumigation.In conclusion, the Mi-ace-2 played an important role in nematicide fosthiazate resistance, and it will serve as a good foundation for further study of the resistant mechanism of root knot nematode on organophosphate nematicides. Using biological and cultural measures to control root-knot nematode effectively would be of great significance to delay the development of resistance of nematicides, to decrease the dosage of chemical and fertilizer, and to protect agricultural ecological environment.