When it comes to irrigation, one of the greatest dangers is salt – the tiny molecule that can wreak havoc on the plants’ ability to function. Yet some plants, in all their complexity, have developed tools that can help them resist even this challenge.
Now, ARS scientists are looking to build on these tools to create new varieties of crop plants that have even greater ability to withstand salinity. In doing so, they may dramatically expand the type and amount of land and irrigation that can support agriculture.
Devinder Sandhu is a research geneticist in the Agricultural Water Efficiency and Salinity Research Unit in Riverside, CA. His most recent work includes developing more salt-tolerant varieties of alfalfa. His focus on this key forage crop is no accident: the crop plays a critical role as a high-protein food source for dairy cattle, and as a legume, it can fix atmospheric nitrogen, thereby improving soil quality. With enhanced salinity tolerance too, the new alfalfa varieties can thrive on degraded lands or with recycled water, reducing competition with high-value crops for premium agricultural resources.
That ability to make use of less-than-ideal conditions has significant implications: recurring droughts and increased demand for surface water have led to greater reliance on groundwater, often of lower quality. In addition, factors like groundwater aquifer subsidence and reduced snowpack are further reducing the availability of high-quality irrigation water.
As a result, growers are increasingly looking to alternative or degraded water sources, such as treated sewage, runoff from greenhouse operations, and saline groundwater. However, these water sources often have high salt concentrations. Developing salt-tolerant crops like alfalfa can help farmers use these degraded water sources in a sustainable way.
In developing the new lines, Sandhu used traditional plant breeding approaches. Beginning with a germplasm collection of 2,700 alfalfa lines, he and his colleagues chose 12 lines with superior performance, then propagated and evaluated them in trials with various salinity levels. Two lines stood out, showing no biomass reduction under salinity levels equivalent to 1/3 seawater. Interestingly, while both lines performed well, their gene expression profiles revealed that they did so using different mechanisms for salinity tolerance.
To enhance salinity tolerance further, the researchers combined component traits from these lines through breeding and continued to test resulting generations against water with higher and higher salt levels. Ultimately, they tested the resulting new alfalfa lines using real seawater from the Pacific Ocean, and they demonstrated the ability to survive – a result that impressed and astonished colleagues in the field.
The team is already thinking about how to get their results into the hands of growers.
“Right now, we are focused on producing sufficient seed for broader testing and potential distribution,” said Sandhu. “We anticipate completing this phase within the next year or two, paving the way to introduce it to the market. What’s really important to us is to ensure that these salt-tolerant alfalfa lines are accessible to farmers, providing a sustainable solution for agriculture in saline environments.”
Importantly, Sandhu’s research on salt tolerance may extend to a wide range of other crops, including cereal crops like wheat and maize; vegetable crops such as tomato, pepper, eggplant, and spinach; legume crops like soybean; and fruit crops like strawberries, grapes, and almonds.
“The basic mechanisms of salt tolerance are often conserved across plant species, allowing insights from one species to inform research in others,” he said. “For closely-related species, the genes and pathways involved in salinity stress are likely to be similar, enhancing the potential for cross-species application. However, certain plants may also exhibit unique mechanisms of salt tolerance, requiring species-specific studies. We think that by leveraging these shared and unique mechanisms, we can extend the impact of our results across diverse agricultural systems.”