Characterization and Genetic Mapping of Resistance to Cotton–Melon Aphid (<scp><i>Aphis gossypii</i></scp>) in Cucumber

ABSTRACT Cotton–melon aphid ( Aphis gossypii ) is a highly destructive pest that causes serious yield losses in cucumber production. IL52, a Cucumis hystrix introgression line of cucumber, exhibits resistance to a number of diseases and also shows strong resistance to aphids. To characterize the type of aphid resistance in IL52, we designed a separate leaf‐disc/no‐choice test and free‐choice test to examine antibiosis and antixenosis, respectively. Our results indicated that IL52 displayed antixenosis resistance to aphids. In other words, when planted with other lines such as CCMC, IL52 was not favourable to aphids. To dissect the genetic basis of antixenosis resistance in IL52, we evaluated a mapping population of 155 lines from CCMC × IL52–derived F 7:8 RIL using free‐choice test for aphid resistance. A major‐effect QTL on Chr2, designated as qRag2.1 ( Resistant to A. gossypii ), was identified as being significantly associated with aphid resistance. The QTL qRag2.1 was mapped to an interval flanked by markers UW085197 and SSR11909, spanning a physical location of 15.14–19.07 Mb, which explained 12.74%–14.03% of the phenotypic variance. Analysis of polymorphisms between the parental lines using resequencing data revealed one gene, CsaV3_2G018180 , with three nonsynonymous amino acid substitutions and a 6‐bp InDel in its coding sequence (CDS). CsaV3_2G018180 encodes a pectinesterase/pectinesterase inhibitor enzyme, designated as CsPEI , which has been reported to regulate pectin methylesterase activity that is implicated in various biological processes. The relative expression level of CsPEI was induced in IL52 post aphid infestation, suggesting it could be a potential candidate gene for aphid resistance.