Tomato susceptibility to Fusarium crown and root rot: effect of grafting combination and proteomic analysis of tolerance expression in the rootstock.

Grafting can enhance the tolerance of vegetable crops to soilborne diseases. The aim of this study was to investigate whether different tomato scion-rootstock combinations may affect the plant susceptibility to Fusarium oxysporum f. sp. radicis-lycopersici (FORL), the causal agent of crown and root rot. A proteomic approach was used to investigate whenever the protein repertoire of the rootstock can be modified by FORL infection, in relation to cultivar susceptibility/tolerance to the disease. To this purpose, plants of tomato hybrids with different vigor, "Costoluto Genovese" (less vigorous) and "Kadima" (more vigorous), were grafted onto "Cuore di Bue" and "Natalia" hybrids, sensitive and tolerant versus FORL infections, respectively. Disease symptoms, plant biomasses, and protein expression patterns were evaluated 45 days after FORL inoculation. The extent of vascular discoloration caused by FORL in tomato plants grafted on "Natalia" rootstock (0.12-0.37 cm) was significantly lower than that of plants grafted on sensitive "Cuore di Bue" (1.75-6.50 cm). FORL symptoms significantly differed between "Costoluto Genovese" and "Kadima" scions only when grafted on sensitive rootstock. Shoot FW of non-inoculated "Kadima"/"Cuore di Bue" combination was 35% lower than "Kadima"/"Natalia", whereas no difference was manifested in inoculated plants. Shoot FW of inoculated "Costoluto Genovese"/"Cuore di Bue" combination was decreased of 39%, whereas that of "Costoluto Genovese"/"Natalia" of 11%, compared to control plants. Proteomic results showed a higher representation of proteins associated with pathogen infection in the tolerant rootstock, compared to the sensitive one, meaning a direct involvement of plant defence mechanisms in the tomato response to the pathogen challenge.