Effect of saponins of Quillaja saponaria extracts in combination with Pseudomonas protegens to control Gaeumannomyces graminis var. tritici in wheat
ABSTRACT Extracts rich in saponins from Quillaja saponaria Mol. and populations of rhizobacteria from the genus Pseudomonas, which produce antimicrobial compounds, have been associated with reduction of the fungus Gaeumannomyces graminis var. tritici, the causal agent of take-all disease, which is responsible for severe loss of wheat (Triticum aestivum L.) crops worldwide. However, there is a limited background on the interaction between these bacteria and natural triterpenoids. The aim of this research was to assess the effect of saponin rich extract on Pseudomonas protegens strains 2,4-diacetylphloroglucinol-producers under in vitro and in plant conditions and determining the synergistic effect to be used together to control G. graminis var. tritici in wheat plants. We determined that 8% and 90% of saponins rich Q. saponaria extracts have a differential effect on P. protegens according to their purity (P ( 0.05). On wheat seedlings, quillaja extract with 90% of saponins did not affect the three antagonistic bacterial strain populations assessed, but affected biofilm formation at saponins concentration of 7360 mg L-1. Pseudomonas protegens strains had a variable antagonist activity in wheat plants, and controlled the fungus when were combined with different concentrations of pure Q. saponaria extract, with the concentration of 1840 ppm reducing the take-all disease in 32.5% with respect to the control inoculated with G. graminis var. tritici (P ( 0.05). However, no synergistic effects when the plant extract was combined with the bacterial strains were observed. These results showed the promising and complexity of combining bacterial and plant extract to develop a biopesticide, which could control this fungal disease.