Altered root exudation and suppression of induced lignification as mechanisms of predisposition by glyphosate of bean roots (Phaseolus vulgaris L.) to colonization by Pythium spp
1997
Liu, L. | Punja, Z.K. | Rahe, J.E.
Several possible mechanisms for the glyphosate induced predisposition of bean roots (Phaseolus vulgaris L.) to colonization by Pythium spp. were investigated. Glyphosate at 0.1 and 1.0 microgram ml-1 from the surfactant-containing formulation Roundup, and the non-surfactant-containing formulation Accord did not affect mycelial growth of Pythium ultimum and Pythium sylvaticum on water agar and cornmeal agar. One microgram per millilitre of glyphosate from both formulations significantly stimulated germination of sporangia of P. ultimum. Germination and growth of germ tubes of P. ultimum were significantly greater in root exudate from bean plants whose primary leaves had been treated with glyphosate than in exudates from non-treated plants. The lignin content of roots was increased significantly when P. ultimum or P. sylvaticum was added to the hydroponic system in which the roots were growing. When glyphosate was applied 2 days prior to Pythium, deposition of lignin in response to Pythium in the bean roots was significantly reduced. These results suggest that predisposition by glyphosate of bean roots to colonization by Pythium spp. may involve changes in root exudates that enhance germination and growth of pathogen propagules, and suppression of a pathogen-induced lignification response by plant roots.
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