Fine mapping of a thrips resistance QTL in Capsicum and the role of diterpene glycosides in the underlying mechanism.

A major thrips resistance QTL in Capsicum was fine-mapped to a region of 0.4 Mbp, and a multidisciplinary approach has been used to study putative underlying mechanisms. Resistance to thrips is an important trait for pepper growers. These insects can cause extensive damage to fruits, flowers and leaves on field and greenhouse grown plants worldwide. Two independent studies in Capsicum identified diterpene glycosides as metabolites that are correlated with thrips resistance. In this study, we fine-mapped a previously defined thrips resistance QTL on chromosome 6, to a region of 0.4 Mbp harbouring 15 genes. Two of these 15 candidate genes showed differences in gene expression upon thrips induction, when comparing plants carrying the resistance allele in homozygous state to plants with the susceptibility allele in homozygous state for the QTL region. Three genes, including the two genes that showed difference in gene expression, contained a SNP that was predicted to lead to changes in protein structure. Therefore, these three genes, i.e. an acid phosphatase 1 (APS1), an organic cation/carnitine transporter 7 (OCT7) and an uncharacterized locus LOC107874801, are the most likely candidates for playing a role in thrips resistance and are a first step in elucidating the genetic basis of thrips resistance in Capsicum. In addition, we show that the diterpene glycoside profiles did not differ between plants with the resistance and susceptibility allele for the chromosome 6 QTL, suggesting that these compounds do not play a role in the resistance conferred by the genes located in the major thrips resistance QTL studied.