Soybean (Glycine max) Response to Glyphosate and Soybean Cyst Nematode (Heterodera glycines)1

Abstract

Field observations in Ohio suggested a possible interaction between soybean cyst nematode (SCN) and glyphosate in Countrymark 316 soybean, a transgenic glyphosate-resistant (R) variety that also expresses SCN resistance derived from ‘PI88788’ soybean. To investigate this possible interaction under controlled conditions, greenhouse experiments were conducted in which Countrymark 316 (R) and Corsoy 79 (S = susceptible to glyphosate and SCN) soybean root and shoot weights were measured in response to three concentrations of race 3 SCN inoculum and five glyphosate doses. Experiments were conducted in which glyphosate was applied 9, 18, or 27 d after inoculation (DAI). Data from SCN treatments in the (S) soybean experiments were regressed on glyphosate dosage and fit to a log-logistic dose–response model. SCN–glyphosate interaction in the (S) soybean variety reduced root dry weight of SCN-inoculated plants 6% compared with noninoculated plants when 1.0 kg/ha glyphosate was applied 18 DAI. The most significant ...