Research Highlights
Improving Drought Adaptation by Insertion of the Limited Transpiration Trait into Soybean

By Avat Shekoofa, The University of Tennessee, Knoxville

Drought conditions in the United States are estimated to result in average annual losses in the range of $10 to $14 billion, and these losses will only increase as the climate changes. The identification of genetic mechanisms for tolerating periods of drought, and the incorporation of those genes into current germplasm for breeding stock, is critical to sustaining crop production and yield. Drought tolerance is a complex problem, as there are multiple mechanisms by which a tolerant soybean can overcome water deficiency. This $56,975 project study is examining one mechanism, called limited transpiration or slow wilting. This is a mechanism by which plants are able to limit the water that exits through the leaf.

To identify expression of limited transpiration (TRlim) (i.e., slow wilting) among soybean lines under high evaporative demand (> 2.5 kPa), over 1,000 de-rooted shoots of 150 upper Mid-south soybean lines were tested with silver nitrate. Among 122 of those lines, half of the population showed higher sensitivity (fast wilting) to silver nitrate than their parents. However, several lines showed no or limited changes in water loss (slow wilting) with the silver treatment. Therefore, after the silver treatment, 26 lines were selected for measuring the whole plant transpiration rate under dry air (i.e., high evaporative demand) in a walk-in growth chamber. All 26 lines were divided into three categories: 1) slow, 2) moderate and 3) fast wilting, based on the silver nitrate test results. The whole plant transpiration results indicated that 71% of the slow, 40% of the moderate and 33% of the fast wilting soybean lines expressed limited water loss, which indicates possible water-saving potential under dry air in a controlled environment. 

Measuring whole plant transpiration rate under high evaporative demand (dry air: > 2.5 kPa) in 2019.

Moreover, DNA is currently being extracted from all 122 lines. Once the sequencing is done and genotypic data is complete, genetic mapping will be used to identify the genomic regions that are controlling limited transpiration (i.e., slow wilting). The soybean lines that showed limited water loss during the whole plant transpiration test will be studied under field conditions in 2020 for seed quality and evaluation as potential drought-tolerant parents in a breeding effort.

The vulnerability of soybean to drought introduces volatility into the market and into growers’ revenue streams. Without intervention and planning, predicted climatic conditions for U.S. soybean production regions will likely exacerbate this problem in the near distant future. This project will provide tools to mitigate this issue. 

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.