Abstract

Extracts rich in saponins from quillay (Quillaja saponaria Mol.), an endemic Chilean native tree, and rhizobacteria of the genus Pseudomonas, which produce antimicrobial compounds such as 2,4-Diacetylphloroglucinol (2,4-DAPG), have been associated with reduction of the fungus Gaeumannomyces graminis var. tritici (Ggt), causal agent of take-all disease of wheat. However, reports about bioactivity between these bacteria and this natural triterpenoids are not available. Through in vitro and in vivo tests the interaction between both new sources of take-all disease control were assessed. Results showed that quillay extracts Vet SAP® (>90% of saponins) and QL1000® (~8% of saponins) controlled Ggt in vitro and had a differential effect according to their purity on populations of 2,4-DAPG-producing P. protegens, with Vet SAP® not affecting the bacterial growth at 800 ppm of quillay saponins. On wheat seedlings, Vet SAP® did not affect the bacterial populations of the three bacterial strains assessed, although, quillay saponins at concentration of 7,360 ppm reduced bacterial biofilm formation on the rhizosphere. Strains of P. protegens had a variable antagonistic activity on wheat seedling roots and kept their disease control ability when were combined with different concentrations of Vet SAP®. These results suggest that mixtures of the antagonistic bacteria and plant extract to control G. graminis var. tritici could be useful in developing a biopesticide.