Feeding Behavior of Aphis gossypii on Resistant Accessions of Different Melon Genotypes (Cucumis melo)

The feeding behavior of the melon aphid Aphis gossypii Glover (Homoptera: Aphididae) was monitored using the electrical penetration graph (EPG) technique on different melon (Cucumis melo L.) genotypes showing resistance to the aphid. The aphid-resistant genotypes used were PI-161375 and PI-414723, sources of the Vat and Agr genes, respectively. TGR-1551, a new C. melo accession from Zimbabwe, was also tested. Our goal was to localize the tissues where the resistance factors are expressed and to determine if the resistance mechanisms operating in the three aphid-resistant accessions were the same. Our results indicated that the three selected lines have resistant factors located at the epidermis, mesophyll and vascular tissues. However, the behavior of A. gossypii on TGR-1551 was different from the two other resistant accessions, as indicated by a longer phloem salivation phase (E1 phase). Many of the E1 phases observed for aphids feeding on TGR-1551 were not followed by phloem ingestion (E2 phase). These results suggest that TGR-1551 has a resistance mechanism that prevents A. gossypii from initiating ingestion from the phloem. Preference tests under free choice conditions also showed that aphids rejected accessions TGR-1551 or PI-414723 faster than PI-161375. Our results support the hypothesis that Agr and Vat are coding for different kinds of resistance strategies. Comparisons of aphid life history parameters also indicated that TGR-1551 is a very promising new source to breed for resistance against A. gossypii.