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Characterization of adaptation to a resistance gene with a pleiotropic effect, the Vat gene in melon

Abstract : The deployment of resistance genes against aphids, is restricted because few genes have been characterised. The Vat gene, conferring resistance to Aphis gossypii, has been effectively deployed in melon crops since 20 years in South-eastern France. We have studied the adaptation of A. gossypii populations to that Vat gene. Seven clones of A. gossypii were collected in melon producing areas where the Vat gene has been or not deployed. Theses clones were characterized using 8 SSR markers. The phenotypic variability of A. gossypii was shown matching the genetic variability revealed by eight microsatellite markers (Thomas et al, 2012). We phenotyped the seven clones using three resistant melon lines. One line was susceptible to ail clones, the two other lines, Margot and 90625, were known to carry different alleles at the Vat locus. We took advantage of the double phenotype mediated by the Vat gene, the resistance to A. gossypii and the resistance to viruses (CMV, ZYMV...) when inoculated by A. gossypii - melon plants are susceptible to viruses when they are mechanically inoculated or inoculated by other aphids species. Aphid clones triggered three phenotypic responses on Margot or 90625 lines: resistance to aphids and to the virus when inoculated by aphids, susceptibility for both phenotypes, and susceptibility to aphids and resistance to the virus when inoculated by aphids; we did not characterize any clones revealing a melon line resistant to aphids and susceptible to virus when inoculated by aphids. Our results revealed a specifie interaction between plant resistance alleles in melon and aphid clones. The Vat gene belongs to the CC-NBS-LRRresistance gene (Pauquet et al 2004). The avirulence factor in aphid, expected to interact with the Vat protein, is presently unknown, it should be excreted in saliva and introduce in plant tissue during puncturing, and then interacts with the Vat product triggering defence responses (Dogimont et al 2010). These responses are expected to be efficient against aphids and viruses. Our results suggested two adaptation mechanisms of aphids to the Vat mediated resistance: i/ suppression of both phenotypes, i.e. susceptibility to aphids and to virus when inoculated by A. gossypii, what suggests a suppression of the recognition step (non-adapted avirulence product), ii/ susceptibility to aphids associated with resistance to virus when inoculated by aphids, suggested that the recognition step occurs, triggering the defence reponses that are efficient against virus but inefficient against aphids, i.e. aphids are adapted to these defence responses. We only observed adaptations of type i/ when considering the melon line 90625. Because the allele of resistance originating from this line has never been deployed in crops in areas we collected clones, these adaptations, observed in several clones, corresponded to an incomplete spectrum of the resistance efficiency. ln South-eastern France, the resistance that has been deployed is mediated by the allele at the Vat locus present in Margot. ln this area, where A. gossypii diversity is very large (Thomas et al 2012b), two clones, never observed before 2009, exhibited adaptation of type ii/ to that allele of resistance.
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https://hal.inrae.fr/hal-02807786
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Submitted on : Saturday, June 6, 2020 - 4:33:25 AM
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  • HAL Id : hal-02807786, version 1
  • PRODINRA : 213989

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Nathalie Boissot, S. Thomas, Virginie Chareyron, Pascale Mistral. Characterization of adaptation to a resistance gene with a pleiotropic effect, the Vat gene in melon. Congrès international plant Resistance sustainability 2012, Oct 2012, La Colle-Sur-Loup, France. 2 p. ⟨hal-02807786⟩

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