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Research Highlights

Research Highlights
Genetic Improvement of Flood Tolerance and Best Management Practices for Sustainable Soybean Production

By Henry T. Nguyen, University of Missouri

Figure 1. A nation concern of flooded farmland. (A) NOAA 2019 spring flood forecast map. Purple, red and orange areas indicate major, moderate and minor flooding, respectively. (B) Flooding is recognized as a national problem. 

Flooding is a major abiotic stress for soybean crops, causing economic losses to U.S. agriculture estimated at $1.5 billion per year (USDA, 2009), a figure which is expected to increase due to climate volatility. Flood damage to crops can be caused by extreme rainfall events, excessive irrigation or by rainfall that occurs after an irrigation event. In the North Central and the Mississippi Delta regions, early-season flooding stress is frequent due to excessive rains in spring and early summer. In fact, the spring floods of 2019 hit the key row-crop growing regions of the U.S. (Figure 1A), impacting more than 66% of the lower 48 states and causing devastation in key agricultural production states. Major disaster declarations were issued by the Federal Emergency Management Agency (FEMA) to parts of Minnesota, Mississippi, Kansas, Alabama, Nebraska, Iowa, Tennessee, Kentucky and Missouri, all states with significant soybean and maize production acres. 

As a major crop in the U.S., soybean is particularly sensitive to soil flooding, and yield is especially subjective to flooding stress. As little as two days of soil flooding can lead to a more than 25% reduction in crop yield, and under extended soil-flooding periods, complete yield losses are expected. Moreover, the National Aeronautics and Space Administration’s (NASA) weather simulation models predict an alarming 30% increase in heavy rains by the year 2030 due to global changes in climate, which will significantly increase the frequency of, and losses caused by, flooding. Heavy precipitation causes soil-flooding stress in crop plants in the lower parts of any field due to poor drainage (Figure 2A), which reduces the exchange of oxygen between the soil and the atmosphere. As few as four days of soil flooding can kill young soybean plants at early stages (Figure 2B) or cause severe injury of larger plants at later growth stages, which may result in delays in plant growth and shorter plants with fewer nodes (Figure 2C). In addition, excessive rains during the seed-filling stage are known to cause significant reduction in seed quality and composition across the entire U.S. soybean production region, as was observed during the 2018 growing season. 

Figure 2. Soil flooding in the field. (A) Standing water at 4-days after a heavy precipitation in Missouri. (B) Damage of soil flooding at seeding stage. (C) Slowing growing and injury of plants at lower spots of the field. 

Therefore, it is imperative that flooding-tolerant and high-yielding cultivars/germplasm be identified and developed to enable the development of new, flood-tolerant soybean crops. This $348,525 project aims to build long-term, value-chain resilience to an increasingly present source of shock — the stress caused by flooding. This project has taken a three-pronged approach: identifying flooding-tolerant genetic resources resistant to both early- and mid-season flooding stress; accelerating the development of flooding-tolerant and high-yielding varieties/germplasm; and optimizing management practices to protect yield from excess water. 

Progress has been made toward all these goals. A well-developed, flood-tolerant breeding pipeline has been established, along with field-screening sites that can be flooded on demand in all five participating states. Specific accomplishments are listed below. 

  1. Novel genetic resources were identified, including six exotic and 10 wild-type soybean lines, which have high tolerance for flooding. From these, six flooding tolerance genes and their associated DNA markers were identified for use in molecular breeding. 
  2. Six populations of soybean germplasm were developed for gene mapping and breeding, utilizing the newly identified genetic resources shown to be flood tolerant. 
  3. Early- and mid-season flooding tolerances were found to share some common features and lineage, but they differed in the tolerance mechanisms, as a low correlation was observed between the genes responsible for early- and mid-season flooding stresses. 
  4. New flooding-tolerant germplasm, such as lines of S12-1362, S15-19625, R04-342 and R07-6669, are in the process of being released as conventional high-yielding germplasm with flooding tolerance (Figure 3). 
  5. Effects of flooding on yield were quantified for the Mississippi Delta region, and a raised-bed production strategy appeared to be promising after field testing several options. 
Figure 3.

Although significant progress has been made, efforts continue to increase flood resilience in soybean. New genetic resources for flooding tolerance at both early- and mid-seasons continue to be identified in both exotic and wild soybean lines. Multiple genes that lead to flood tolerance can be stacked in a single germplasm, and this stacking is expected to develop stronger flooding tolerance. New breeding strategies aimed at fully utilizing marker-assisted selection are currently being evaluated, and novel flood-tolerant wild soybean is being used in applied breeding, in order to incorporate new genetics for flood tolerance into existing, high-yielding elite lines. 

Furthermore, the negative effect of excessive rains at the seed-filling stage on soybean seed quality and composition are being examined. In the short term, novel genetic resources for flooding tolerance will be identified and utilized to develop new and improved flooding-tolerant germplasm to support variety development. Best management practices will be evaluated, validated and recommended for flooding-prone areas. 

The long-term benefit of this project will be its contribution to the development of flooding-tolerant varieties for flooding-prone areas, along with the latest production techniques to maximize profit opportunities. Flood-tolerant germplasm grown with experimentally proven flood-resistant management can improve yield up to 50-70% under flooding stress. 

The development of new germplasm that is significantly more flood-tolerant, and a better understanding of flood management practices, will benefit U.S. soybean producers across the country, wherever excessive water from heavy precipitation and irrigation is a problem. Especially as flooding increases over the next 20 years, this research will become ever more important. 

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.