Xylomic Traits for Rootstock x Scion x Environment Interactions in Tomato

Grafting onto rootstocks (R) is a surgical technique that enables greater adaptability of elite scion (S) varieties to adverse environments (E). Although this is an ancient agricultural technique that is commercially exploited in several crops, the implementation of suitable RxSxE combinations in Solanaceous, Cucurbitaceous and other high-value vegetable crops represents an untapped opportunity to secure yield stability and reliability under biotic and abiotic stresses (Albacete et al., 2015). However, the current practice only scratches the surface of the vast genetic diversity available, while there is a need, an opportunity and a market for rootstock breeding and use. New useful genetic variations can be introduced as R, but also new genotype interactions can be generated in RxS combinations in a range of stressful environments. Information from gene expression, metabolomics in the xylem (xylomics, with hormones playing an essential role) and epigenetic studies, identifying the underlying mechanistic bases of the new phenotypes, will provide new tools to improve identification and prediction of new variants to improve yield, yield stability and quality. Indeed, by using high throughput U-HPLC-MS technology, about 800 metabolites in a range of m/z 90-500 have been detected in the root xylem sap of grafted tomato plants, identifying rootstock-genotype specific metabolomic fingerprinting. The number of those metabolites with a biological effect in the scion needs to be addressed. Genetic markers of those traits can be identified from recombinant inbred populations through rootstock phenotyping, QTL and fine mapping analyses.