Microsphere stem blockage as a screen for nitrogen fixation drought tolerance in soybean

Authors: PRADHAN, DEEPTI - North Carolina State University; BERTIN, DIANA - Luiz De Queiroz College Of Agriculture (ESALQ); SINCLAIR, THOMAS - North Carolina State University; NOGUERIA, MARCO - Embrapa; Livingston, David; CARTER, THOMAS - Retired ARS Employee

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2020
Publication Date: 12/5/2020
Citation: Pradhan, D., Bertin, D., Sinclair, T., Nogueria, M., Livingston, D.P., Carter, T. 2020. Microsphere stem blockage as a screen for nitrogen fixation drought tolerance in soybean. Physiologia Plantarum. https://doi.org/10.1111/ppl.13281.
DOI: https://doi.org/10.1111/ppl.13281

Interpretive Summary: Drought conditions have a significant effect on the ability of soybean plants to fix nitrogen, but it is currently difficult to identify soybean lines that are drought tolerant. In this study a technique was devised that will give breeders a way to select breeding lines that are more drought tolerant which ultimately will result in soybean cultivars with higher yeilds. Previous research has shown that varieties with large water conducting vessels are not as drought tolerant as those with small vessles. So, in this study stems of that were placed into a solution of very small microbeads were allowed to draw the beads into water conducting vessels to see if the vessels of a certain size could be blocked. Genotypes with larger vessels were plugged by the microspheres and their ability to conduct water was inhibited which caused them to wilt and allowed a visual identification of. Varieties in which microspheres did not plug water vessels were those that had been identified previously as drought tolerant, which confirmed that this microsphere test could be used to determine genotypes that were resistant to drought stress.

Technical Abstract: Symbiotic nitrogen fixation of soybean (Glycine max (Merr.) L) is commonly quite sensitive to soil drying. Decreases in the rate of nitrogen fixation with soil drying occur before decreases in transpiration rate, or other physiological processes, which imposes a limitation on yield in the production of high-protein content soybean seeds. While a few soybean lines that have nitrogen fixation drought tolerance have been identified, exploitation of this genetic diversity is hampered by the very laborious process of phenotyping nitrogen fixation drought tolerance. The objective of this research was to examine earlier suggestions that nitrogen fixation drought tolerance might correspond with fewer large-diameter xylem vessels in the stem. Phenotyping was done on two soybean populations by exposing de-rooted shoots to a suspension of microspheres and characterizing the blockage of the vessels by decreases in transpiration rate. In a population of 16 genotypes previously screened for nitrogen-fixation drought-tolerance, most lines showed low or intermediate response to the microsphere treatment. That is, these tolerant lines had fewer larger-diameter xylem vessels in which the microspheres could enter and inhibit water flow. However, there were exceptions to this correspondence since three lines with nitrogen fixation drought tolerance exhibited large responses to the microsphere treatment. In a population derived from a cross of parents with high and low nitrogen fixation sensitivity to drought, there was wide variation in response to the microsphere treatment. There was, however, a signification correlation (R2 = 0.68; p<0.001) between increasing response to the microsphere treatment and increasing sensitivity of nitrogen fixation to soil drying. Overall, the microsphere treatment could be useful in soybean as a screen to phenotype lines for potential nitrogen fixation drought tolerance.