"Effects of glypohsate on Bradyrhizobium japonicum interactions in Roundup-Ready
soybeans"
(Abstract)
R. E. Hoagland*, K. N. Reddy, and R. M. Zablotowicz
1999 Weed Science Society of America Abstracts
Vol 39, 1999
Transgenic crops resistant to herbicides [e.g., glyphosate-tolerant (Roundup-Ready, RR) soybeans], are a promising weed control strategy. Because of a lack of published information on the B. japonicum - soybean symbiosis in glyphosate-treated RR soybeans, we examined conventional (DP 3588) and RR soybeans (DP 5806 RR) for glyphosate effects on plant growth, chlorophyll content, nodulation, and nodule leghemoglobin content, two weeks after application in the greenhouse. In DP 3588, a single application of 0.28 kg ha"1 two weeks after planting reduced chlorophyll content (49%) and shoot and root dry weight (50 & 57%, respectively). In DP 5806 RR, there were no significant effects on these parameters by single applications up to 1.12 kg ha' , but 2.24 kg ha' reduced shoot and root dry weight by 25 to 30%. Glyphosate at 0.28 kg ha'1 reduced nodule mass and number by 75% and 33%, respectively, in DP 3588 compared to untreated plants. Two tests assessed effects of 1.12 or 2.28 kg ha'1 glyphosate on DP 5806 RR applied two weeks after planting. A significant reduction in nodule mass and number occurred in only 1 test, and only at 1.12 kg ha'1. Leghemoglobin content was reduced by glyphosate in both tests, but effects were inconsistent with rate. Application of 1.12 kg ha' three weeks after planting did not affect nodule number or mass, but 2.24 kg ha' reduced these parameters 30 and 39%, respectively, compared to untreated. Leghemoglobin content was reduced (10 to 18%) by both glyphosate rates. Subtle reductions of nodulation in RR soybeans using label rates of glyphosate can occur, but these effects may be of minimal consequence due to the potential of soybeans to compensate for short durations of stress.
R. E. Hoagland
USDA-ARS, SWSRU, Stoneville, MS.
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