Image-based high-throughput phenotyping of grafted tomato plants upon virus or viroid infection.

Grafting is an agronomic technique used as a sustainable integrated strategy for the management of biotic and abiotic stresses. Besides improving the performance of several horticultural crops, grafting can enhance the tolerance to viral infections in tomato. Whether grafting may interfere also with viroid infections in this host plant is still unknown. Here, we investigated by high-throughput phenotyping (Scananalyzer 3D system) the responses of grafted and non-grafted tomato plants to infections with potato spindle tuber viroid (PSTVd) or a recombinant strain of potato virus Y (PVYc-to), which elicit stunting and leaf curling or severe leaf distortion and mosaic in this host, respectively. Two tomato varieties, Manduria (Ma) and UC82 (UC), tolerant and highly susceptible to PVYc-to infection, respectively, were tested. Non-grafted, self-grafted UC (UC/UC) and UC grafted onto Ma (UC/ Ma) plants were mechanically inoculated with PVYc-to, PSTVd or mock-inoculated. Quantitative data of morphological parameters were acquired at 9 time points up to 36 dpi. PCA analysis showed that grafting has a global effect on PSTVd and PVYC-to infection, with a slightly positive effect of UC/Ma with respect to self-grafted tomato plants. Moreover, a delay in viroid-induced stunting and a reduced accumulation of the viroid were observed in the grafted plants. A slight increase in plant area, silhouette and solidity values were measured in grafted-PVYc-to plants compared to the non-grafted counterparts starting at 15 dpi, associated with the lower viral load. These preliminary results show that highthroughput phenotyping is a promising tool to estimate tomato response across PVYC-to and PSTVd infections.