Soybean response to nodulation by bradyrhizobia differing in rhizobitoxine phenotype |
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Authors: | George B Teaney III Jeffry J Fuhrmann |
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Institution: | (1) Delaware Agricultural Experimental Station, Department of Plant and Soil Sciences, College of Agricultural Sciences, University of Delaware, 19717-1303 Newark, DE, USA |
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Abstract: | Rhizobitoxine-producing (RT+) strains of Bradyrhizobium japonicum, differing in their abilities to induce foliar chlorosis with ‘Forrest’ soybean (Glycine max L.] Merr.), were evaluated for effects on short term shoot productivity, nodulation, N2 fixation, and nodule protein production under greenhouse conditions. Soybeans were singly inoculated with washed suspensions
of (Group II) USDA strains 31, 46, 76, 94, 110, 123 or 130. Strains USDA 110 and USDA 123 (Group I/Ia) were included as RT-controls.
The plants were cultured in the absence of combined N in horticultural-grade vermiculite for 49 days. Beginning 21 days after
planting, plants were evaluated weekly for chlorophyll, leaf protein and biomass accumulation, nodular contents of leghemoglobin,
soluble protein and RT, and total shoot N content. Rhizobitoxine was detected in nodules of all RT+ strains with the exception of USDA 31. However, only USDA 76 and USDA 94 produced both quantifiable concentrations of RT
and symptoms of RT-induced chlorosis. Coincident with moderate to severe chlorosis were reductions in chlorophyll concentrations,
shoot and nodule dry weight, leaf protein and total N2 fixation. During extended periods of severe chlorosis, reductions in Lb and soluble nodular protein were observed. Based
on carbon accumulation, all non-chlorotic treatments were statistically more productive than the chlorotic treatments. Similarly,
non-chlorotic Group II treatments tended to fix less carbon relative to the RT-Group I/Ia controls, although these differences
were not statistically significant. The results of this study suggest that, in the absence of discernable foliar chlorosis,
the effect of RT+ (Group II) nodulation on short term soybean productivity is minimal.
Published as Miscellaneous Paper No. 1439 of the Delaware Agricultural Experiment Station.
Published as Miscellaneous Paper No. 1439 of the Delaware Agricultural Experiment Station. |
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Keywords: | Bradyrhizobium japonicum chlorophyll leghemoglobin nodule protein rhizobitoxine |
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