Induction of resistance in tomato plants against Fusarium oxysporum f. sp. lycopersici mediated through salicylic acid and Trichoderma harzianum

The effect of a soil application of salicylic acid (SA) and a biocontrol agent, Trichoderma harzianum (TH) on the induction of phenolic accumulation content and defense enzymes in tomato plants infected with Fusarium oxysporum f. sp. lycopersici (F. oxysporum) was investigated. The phenolic content was recorded to be higher in all the treatments viz. F. oxysporum, F. oxysporum + TH, F. oxysporum + SA and F. oxysporum + TH + SA than that of the healthy plants and reached its maximum level in the plants treated with F. oxysporum + TH + SA. Tomato plants treated with different concentrations of SA (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mM) showed significant increases in the activities of both peroxidase and polyphenol oxidase where a prominent enhancement was observed at a 1.5 mM concentration of SA. F. oxysporum infection resulted in the induction of both of the enzyme activities but at a lower level. The activities of both peroxidase and polyphenol oxidase reached their maximum on the 28th day, when the plants were treated with F. oxysporum and SA (1.5 mM). The combined application of SA (1.5 mM) and TH in Fusarium infected tomato plants, also enhanced the activities of both of the enzymes.