Effect of drought on Bradyrhizobium japonicum populations in Midwest soils
Background and aims
Bradyrhizobium japonicum and soybean (Glycine max (L.) Merr.) form a symbiotic association which allows for biological nitrogen fixation (BNF) to help meet the nitrogen (N) requirement of soybean plants. Rhizobial inoculants are not always used in soybean production in the Midwestern USA because of high naturalized soil populations, but drought conditions experienced in the region during the 2012 growing season may have led to a decline in numbers resulting in the need for inoculation the following growing season. Therefore, the effect of drought on B. japonicum population size was investigated in this study.
Drought conditions, 8 weeks long or 4 weeks long preceded (STOP) or followed (START) by 4 weeks of normal watering, were simulated in two contrasting soil types in a greenhouse setting with soybeans as host plants. Drought conditions were monitored by measuring water content. Population size of B. japonicum was quantified using quantitative real-time polymerase chain reaction (qPCR) and most probable number (MPN) methods and compared to population from non-drought treatment.
Using both quantification methods, the response of B. japonicum to drought treatments was minimal.
Drought conditions 4 to 8 weeks long did not reduce B. japonicum population size to levels which would affect soybean growth and development.
KeywordsDrought Rhizobia Quantitative PCR MPN Inoculants Nitrogen fixation
- Barker DG, Pfaff T, Moreau D, Groves E, Ruffel S, Lepetit M, Whitehand S, Maillet F, Nair RM, Journet EP (2006) Growing M. truncatula: choice of substrates and growth conditions. http://www.noble.org/MedicagoHandbook/pdf/GrowingMedicagotruncatula.pdf. Accessed 13 December 2013
- Conley SP, Christmas EP (2005) Utilizing inoculants in a corn-soybean rotation. http://www.ces.purdue.edu/extmedia/SPS/SPS-100-W.pdf. Accessed 13 December 2013
- Littell RC, Milliken GA, Stroup WW, Wolfinger RD, Schabenberger O (2006) SAS for mixed models, 2nd edn. SAS Institute, CaryGoogle Scholar
- Sprent JI (1971) Effects of water stress on nitrogen fixation in root nodules. Plant Soil (Spec Vol), 225-228Google Scholar
- US Drought Monitor (2012) Drought monitor archives. http://droughtmonitor.unl.edu/archive.html. Accessed 1 December 2013
- Vincent JM (1970) A manual for the practical study of root-nodule bacteria. Blackwell, OxfordGoogle Scholar