Induced systemic resistance to wheat take-all disease by probiotic bacteria

In this study, the effect of six commercial biocontrol strains, Bacillus pumilus INR7, B. megaterium P2, B. subtilis GB03, B. subtilis S, B. subtilis AS and B. subtilis BS and four indigenous strains Achromobacter sp. B124, Pseudomonas geniculate B19, Serratia marcescens B29 and B. simplex B21 and two plant defense inducers, methyl salicylate (Me-SA) and methyl jasmonate (Me-JA) were assessed on suppression of wheat take-all disease. Treatments were applied either as soil drench or sprayed on shoots. In the soil drench method, the highest disease suppression was achieved in treatment with strains INR7, GB03, B19 and AS along with two chemical inducers. Bacillus subtilis S, as the worst treatment, suppressed take-all severity up to 56%. Both chemical inducers and bacterial strains AS and P2 exhibited the highest effect on suppression of take-all disease in the shoot spray method. Bacillus subtilis S suppressed the disease severity up to 49% and was again the worst strain. The efficacy of strains GB03 and B19 decreased significantly in the shoot spray method compared to the soil drench application method. Our results showed that most treatments had the same effect on take-all disease when they were applied as soil drench or sprayed on aerial parts. This means that induction of plant defense was the main mechanism in suppressing take-all disease by the given rhizobacteria. It also revealed that plant growth was reduced when it was treated with chemical inducers. In contrast, rhizobacteria not only suppressed the disease, but also increased plant growth.