Agricultural soils are growing saltier—and that’s bad news for plenty of crops. But a hardy tomato relative from the deserts of Peru might hold the key to a future where at least this ubiquitous salad ingredient continues thriving in a climate-changed world.
Researchers detail this discovery in a recent study published in The Plant Journal: they followed a hunch that the closest living wild relative of the common tomato, a diminutive species known as the currant tomato or Solanum pimpinellifolium—so small that it appears more like a berry than tomato—holds untapped genetic secrets thanks to its large diversity.
To find out, they grew over 2,700 cultivars of the currant tomato, raising these seedlings in two environments: a greenhouse, and an open field. They exposed some plants in each location to varying levels of salt stress for two weeks.
Before the experiment, the researchers had identified various traits and markers to watch for as the plants grew, and which they suspected would change under variable salinity. These included shoot growth, sodium ion accumulation (a marker of how much salt the plant absorbs from the soil) and the rate at which plants transpire water from their leaves. Each was meticulously measured as the plants grew.
Bearing these markers in mind, the researchers also paid special attention to plants and cultivars that seemed to be growing well under the stressful saline conditions.
The close inspection revealed that currant tomato plants have a wide and varied response to salinity stress—but that five cultivars in particular scored well on several fronts. For these, the most useful traits differed by location, with greenhouse plants surviving salinity if they transpired more efficiently, i.e. lost less water, while field plants performed better if they had a greater shoot mass.
One of the strongest predictors of salinity resistance across the board was how vigorously plants grew: those with strong, bushy growth that developed quickly withstood saltier soils better than the rest.
Researchers had assumed that these healthy plants would have accumulated fewer sodium ions in their leaves, suggesting that salt-resilient plants have a way of avoiding excessive uptake from the soil. But in fact, they found this was not true, with healthier plants holding plenty of sodium ions in their tissues, which calls into question predominant ideas about how some plants deal with salt stress.
One possibility, the researchers think, is that while the larger, healthier plants do take up salt from the soil, crucially they can spread it more evenly over their larger leaf network, dispersing the effects.
Interestingly, the five promising cultivars that the researchers identified originate from two regions in Peru that are renowned for having some of the most arid conditions in the world. This might help explain why those cultivars coped comparatively well with the hostile soil conditions.
This has prompted researchers to hunt through those cultivars for genes that could be bred into other tomato crops—particularly those associated with water-use efficiency like some of the efficiently-transpiring greenhouse cultivars showed, and genes that help to maintain growth rates against the odds, like the thriving outdoor cultivars managed to do.
They’ve already made a start on this, and have identified three loci on the currant tomato’s genome, where there are genes linked to these favorable traits— and which interestingly have not previously been connected to salt tolerance.
Next, they’ll be poring over these candidates to understand how they boost tomato growth in saline soils—and the benefits may go beyond tomatoes alone, the researchers believe. “These specific genotypes can be used as allele donors for further improving crop performance and developing more sustainable agriculture,” they say.
Julkowska et. al. “Deciphering salt stress responses in Solanum pimpinellifolium through high-throughput phenotyping.” The Plant Journal. 2024.
Image: based on photo by Anastasiya Badun.©Anthropocene Magazine
