Salicylic acid-induced resistance to Fusarium oxysporum f. sp. lycopersici in tomato.

We demonstrated that exogenous application of 200 microM salicylic acid through root feeding and foliar spray could induce resistance against Fusarium oxysporum f. sp. Lycopersici (Fol) in tomato. Endogenous accumulation of free salicylic acid in tomato roots was detected by HPLC and identification was confirmed by LC-MS/MS analysis. At 168h of salicylic acid treatment through roots, the endogenous salicylic acid level in the roots increased to 1477ngg(-1) FW which was 10 times higher than control plants. Similarly, the salicylic acid content was 1001ngg(-1) FW at 168h of treatment by foliar spray, which was 8.7 times higher than control plants. The activities of phenylalanine ammonia lyase (PAL, EC 4.3.1.5) and peroxidase (POD, EC 1.11.1.7) were 5.9 and 4.7 times higher, respectively than the control plants at 168h of salicylic acid feeding through the roots. The increase in PAL and POD activities was 3.7 and 3.3 times higher, respectively at 168h of salicylic acid treatments through foliar spray than control plants. The salicylic acid-treated tomato plants challenged with Fol exhibited significantly reduced vascular browning and leaf yellowing wilting. The mycelial growth of Fol was not significantly affected by salicylic acid. Significant increase in basal level of salicylic acid in noninoculated plants indicated that tomato root system might have the capacity to assimilate and distribute salicylic acid throughout the plant. The results indicated that the induced resistance observed in tomato against Fol might be a case of salicylic acid-dependent systemic acquired resistance.