Grafting: an amenable way to menage virus infections in tomato crops.

Vegetable grafting may be an integrated pest management strategy for tomato crops to limit negative impacts of intensive cultivation and global movement of known and new pathogens. Grafting of commercial tomato varieties and hybrids onto the Apulian (southern Italy) variety "Manduria" (Ma) resulted in high levels of tolerance to the infection of Sw5 resistance-breaking strains of tomato spotted wilt virus (TSWV) and of severe cucumber mosaic virus (CMV) strains supporting hypervirulent satellite RNAs (satRNAs). In the most recent study, we used the Ion-Torrent next generation sequencing technology to determine the transcriptome profiles of the tolerant Ma variety and of the susceptible variety UC82, and of three graft combinations (UC/UC, Ma/Ma and UC/Ma), exposed or not to infection of the potato virus Y recombinant strain (PVYC-to), necrogenic to tomato. The analysis identified graft- and virus-responsive mRNAs differentially expressed in the two varieties, which led to an overall suitable level of tolerance to viral infection, ended with the appearance of a recovery phenotype. The number of differentially expressed genes (DEGs) was higher in mock-inoculated plants compared to their infected counterparts. The Ma variety was less responsive to both the stresses compared to the UC82 variety. We propose that this lower responsiveness to both the stimuli (grafting and viral infection) could be the basis for the tolerance to viral infection observed in commercial tomato varieties and hybrids grafted onto the Ma variety.