The effect of salicylic acid on resistance in wheat (Triticum aestivum) seedling roots against the Take-all fungus Gaeumannomyces graminis var. tritici

The effect of salicylic acid (SA) applied as foliar dip, foliar wipe, root drench or pre-germination soak on the susceptibility of wheat (Triticum aestivum L.) seedlings to Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker (take-all fungus, Ggt) was studied. It was hypothesised that an increase in SA concentration applied using these methods would increase the resistance in wheat seedling roots against Ggt. Leaves (by foliar wipe and foliar dip) and roots (by root drench) of 1-2-week-old wheat seedlings grown in Lancelin sand, were treated with 0, 0.1 or 1 mM SA, and treatments of 0, 0.1 or 0.5 mM SA were applied in a pre-germination soak method. Ggt infection reduced (P less than or equal to 0.05) chlorophyll content and concentration and root length (P less than or equal to 0.10). Experiments that were conducted suggested that the SA treatments failed to induce a resistance response because they did not stimulate phenylalanine ammonia-lyase and peroxidase activities in the wheat seedling roots. Therefore, SA applied using these methods was not effective in reducing the susceptibility of wheat seedlings to Ggt. The chemical or biological induction of resistance in plant roots and its applicability as a root disease control strategy requires further clarification.