Concentration-dependent effect of salicylic acid application on wheat seedling resistance to take-all fungus, <Emphasis Type="Italic">Gaeumannomyces graminis</Emphasis> var. <Emphasis Type="Italic">tritici</Emphasis>

Application of 0.1 and 0.2 mM salicylic acid (SA) significantly reduced take-all disease caused by Gaeumannomyces graminis var. tritici (Ggt) and increased the root and shoot lengths and biomass, whereas 0.5 and 1 mM SA had no significant effect. The effective SA concentrations also increased the activities of soluble peroxidase (SPOX) and cell-wall-bound peroxidase (CWPOX) and the concentration of total phenolic compounds. SPOX activity was highest at days 4 and 3 in healthy roots and those inoculated with Ggt, respectively, and that of CWPOX at day 6 in both healthy and inoculated roots. The concentration of phenolic compound was also highest at day 3 in both healthy roots and those inoculated with Ggt. The results indicate that the protective effect of SA depends on certain concentrations which increase peroxidase activity and phenolic compounds accumulation in the wheat roots; higher SA concentrations did not differ from the controls.