A suspected glyphosate-resistant (R) junglerice population was collectedfrom a glyphosate-R corn field near Durham in northern California whereglyphosate had been applied at least twice a year for over 6 yr. Based onthe amount of glyphosate required to reduce growth by 50% (ED50),the R population was 6.6 times more R than the susceptible (S) standardpopulation. Based on the glyphosate concentration that inhibits EPSPS by 50%based on shikimate accumulation (I50) in leaf discs, R plantswere four times more R than S plants. By 3 d after treatment with 0.42 kg ae ha−1 glyphosate, the S population had accumulatedapproximately five times more shikimate than the R population. Nodifferences in [14C]-glyphosate uptake and translocation weredetected between R and S plants. However, partial sequencing of the EPSPS gene revealed a mutation in R plants causing aproline to serine change at EPSPS position 106 (P106S). Our results revealthe first case of a P106S target site mutation associated with glyphosateresistance in junglerice.
