Bacterial secondary metabolites: Possible mechanism for weed suppression in wheat.

Abstract

Chemical weed control is an effective method, but has proved hazardous for humans, environment, and soil biodiversity. Use of allelopathic bacteria (AB), may be more efficient and sustainable weed control measure. The bacterial inoculants never studied in context of their interaction with weed root exudates and precursor-dependent production of the natural phytotoxins (cyanide, cytolytic enzymes and auxin) by these stains to understand their weed suppression and wheat growth promotion abilities. Therefore, root exudates of Avena fatua, Phalaris minor, Rumex dentatus and wheat were quantified and their role in microbial root colonization and secondary metabolites production i.e. cyanide, cytolitic enzymes, phenolics and elevated auxin concentration was studied. The results depicted L-tryptophan and glycine as major contributor of elevated cyanide and elevated levels in weed rhizosphere by the studied Pseudomonas strains, through their higher root colonization ability in weeds as compared to wheat. Furthermore, the higher root colonization also enhanced p-coumaric acid (photosynthesis inhibitor by impairing cytochrome c oxidase activity in plants), and cytolytic enzymes (root cell wall degradation) concentration in weed rhizosphere. In conclusion, the differential root colonization of wheat and weeds by these strains is responsible for enhancing weed suppression (enhancing phytotoxic effect) and wheat growth promotion (lowering phytotoxic effect).