EFFECT OF PYTHIUM SPP AND GLYPHOSATE ON PHYTOALEXIN PRODUCTION AND EXUDATION BY BEAN (PHASEOLUS-VULGARIS L) ROOTS GROWN IN DIFFERENT MEDIA

Kievitone, phaseollinisoflavan and phaseollin were detected in roots o f bean seedlings (Phaseolus vulgaris L.) grown in natural soil. Compar ison of phytoalexin production by roots grown in different media indic ated that these phytoalexins were probably induced by microorganisms i n soil. The influence of common root rot pathogens of bean, Pythium sp p., on phytoalexin production was determined. Pythium ultimum elicited kievitone, phaseollinisoflavan and phaseollin in roots grown in steri lized silica sand. P. sylvaticum induced only kievitone and phaseollin in the same growth medium. Glyphosate did not significantly affect th e accumulation of phytoalexins within 3 days. However, by day 5, signi ficantly more phaseollin was detected in the roots of Pythium inoculat ed plants treated with glyphosate than in Pythium inoculated plants no t treated with glyphosate. In a hydroponic system, both Pythium spp. e licited accumulation of kievitone and phaseollin in root tissue, and b oth phytoalexins were exuded into the bathing solution. Glyphosate app lication did not significantly affect accumulation or exudation of phy toalexins by bean roots in the hydroponic system. The results from thi s study illustrate the nature and extent of phytoalexin production by bean roots in the absence and presence of microbes. (C) 1995 Academic Press Limited