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Abstract
The root-knot nematode Meloidogyne incognita causes severe damage to continuously cropping vegetables. The control of this nematode relies heavily on organophosphate nematicides in China. Here, we described resistance to the organophosphate nematicide fosthiazate in a greenhouse-collected resistant population (RP) and a laboratory susceptible population (SP) of M. incognita. Fosthiazate was 2.74-fold less toxic to nematodes from RP than that from SP. Quantitative real-time PCR revealed that the acetylcholinesterase2 (ace2) transcription level in the RP was significantly higher than that in the SP. Eighteen nonsynonymous amino acid differences in ace2 were observed between the cDNA fragments of the RP and SP. The acetylcholinesterase (AChE) protein activity in the RP was significantly reduced compared with that in the SP. After knocking down the ace2 gene, the ace2 transcription level was significantly decreased, but no negative impact on the infection of juveniles was observed. The 50% lethal concentration of the RNAi RP population decreased 40%, but the inhibition rate of fosthiazate against AChE activity was significantly increased in RP population. Thus, the increased fosthiazate insensitivity in the M. incognita resistant population was strongly associated with mutations in ace2. These results provide valuable insights into the resistance mechanism of root-knot nematode to organophosphate nematicides.
Highlights
The root-knot nematode (RKN) Meloidogyne incognita is widely distributed in soils cultivated with vegetables, causing losses of up to $400 million annually[1]
The amino acid sequences deduced from the nucleotide acid sequences revealed 18 nonsynonymous differences between the resistant population (RP) and susceptible population (SP) populations
Resistance to fosthiazate can be a serious problem in the RKN M. incognita because OP nematicides are effective control agents that are frequently and regularly used in greenhouse crops
Summary
The root-knot nematode (RKN) Meloidogyne incognita is widely distributed in soils cultivated with vegetables, causing losses of up to $400 million annually[1]. Some biological agents, such as avermectins[1,4], Paecilomyces lilacinus[5], Bacillus methylotrophicus[6], and Pochonia chlamydosporia, have been used to control RKNs with high dosage[7,8] These biological agents are expensive, limiting the feasibility of their extensive use[9]. High-efficacy but low-cost nematicides, such as organophosphates (OPs) and carbamates (CBs), have been widely used as alternatives to control RKNs3,10,11. We present the results of an investigation of a greenhouse population of M. incognita from China showing low-level resistance to the OP nematicide fosthiazate and provide evidence of the underlying resistance mechanism. Bioassays and RNA interference (RNAi) data indicated that this resistance largely reflected increased AChE insensitivity, and mutations in the ace[2] gene were associated with resistance to fosthiazate in M. incognita
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