Genetics and mechanism of Aphid resistance in Capsicum

Plant Breeding, Wageningen University and Research (WUR-PB), together with leading Dutch pepper breeding companies have evaluated wild relatives of the cultivated pepper for resistance against the aphid Myzus persicae. This has resulted in the identification of a resistance source on which M. persicae shows a strongly reduced reproduction rate.

In this project we analyze the genetics of the resistance and study the resistance mechanism to facilitate its use in breeding aphid resistant pepper varieties. An F2 population derived from a cross between an aphid resistant and susceptible plant was available for the project.

A QTL mapping was carried out, resulting in the identification of one major QTL explaining 40% of the variation and a minor QTL explaining 7%. The major QTL identified was validated using F3 lines. A start was made with fine mapping the gene underlying the major QTL, which resulted in the identification of a region containing 4 candidate genes. Three M. persicae populations from different geographical origins (W,S, and B) responded differently to the resistance, ranging from strongly affected to hardly affected. The performance of the 3 M. persicae populations was further analysed with respect to the production of reactive oxygen species (ROS), callose deposition and EPG analysis. It was shown that the W population induced the strongest ROS and callose signal in the phloem vessels on the resistant line, followed by the B population and the S population. There was no callose deposited or ROS induced in the susceptible line. EPG analysis showed that aphids of the W population encountered resistance components in the phloem, especially effecting the sustained uptake of phloem sap, which were not seen with the B and S population.