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.

摘要

Glyphosate from non surfactant-containing Accord did not affect in vitro mycelial growth of Pythium ultimum, on either autoclaved water agar (WA) or corn meal agar (CMA), and P. sylvaticum on CMA at any of the concentrations used. On WA, 100.0μg/mlof glyphosate significantly reduced the growth of P. sylvaticum. Surfactant-containing Roundup [glyphosate] at high concentrations reduced mycelial growth of both species significantly on both CMA and WA. Root exudates from treated bean cv. Tender Greenseedlings significantly increased germination of sporangia and growth of germ tubes in Pythium spp. compared with root exudates from untreated plants. By 24 h after application of glyphosate to foliage, the total amount of amino acids in the exudates ofthe treated plants was significantly greater than in the exudates of control plants. Glyphosate applied 2 days prior to inoculation significantly suppressed Pythium-induced lignification. It is suggested that increased colonization of glyphosate-treatedbean roots by Pythium spp. may be due to suppression of lignification and altered properties of root exudates.