Defence responses to nematodes and viruses induced by treatments with ozone in tomato

"Ozone is widely used as a disinfectant, and ozonated water has been known to confer some protection of plants against several biotic stresses. By applying four foliar spray treatments of ozonated water (10 ppm ozone) on tomato seedlings, i.e. two pre- and two post-inoculation with Tomato spotted wilt virus (TSWV), we observed reduction of disease incidence and severity by 20%, as well as a virus titrr reduction by 80% at 19 days post-inoculation. The same treatments also reduced the number of galls induced by root knot nematode (RKN; Meloidogyne incognita) by 29%. Soil drenching with ozonated water for four consecutive days before inoculation reduced RKN gall formation by 60%, but not TSWV infection. Overall, in mock-inoculated plants, foliar sprays induced PR1b1 expression in leaves, though other salicylate- (PAL and PR-5x) or jasmonate-dependent genes (LoxD, AOS and PinI) were substantially unaffected. Soil drenching promptly enhanced transcription of PAL and PR1b1 in roots and leaves, down-regulated PR-5x and did not affect expression of LoxD and AOS. PinI was significantly down-regulated only in leaves. The impact of ozonated water applications on the expression of these genes did not correlate with that of benzothiadiazole, a known inducer of systemic acquired resistance. This demonstrates that ozonated water may protect tomato from two very different biotic stresses, especially when applied at the sites of their infection, and modulates salicylate and jasmonate pathways differently from benzothiadiazole. This research was supported by the Fondazione Cassa di Risparmio di Puglia, Italy, within the Project 'Risposte di difesa contro nematodi e virus indotte da trattamenti di ozono in pomodoro'."