Plant biologists have genetically engineered a tomato plant that can thrive in salty irrigation water. This could open the way towards other salt-tolerant crops and also a method to renew soils damaged by repeated irrigation.
Each year the world loses an estimated 24.7 million acres of once agriculturally productive land because of irrigation-induced salinity, according to US figures. That is more than twice the total amount of land committed to agriculture in the Republic.
Crop production is limited by salinity on 40 per cent of the world's irrigated land and even developed countries are struggling with this problem. Up to a quarter of irrigated land in the US is affected by the build-up of salts, according to the US Department of Agriculture.
Scientists have been trying to develop salt-tolerant crop varieties for decades using selective breeding. Now genetic manipulation involving the insertion of an extra plant gene has allowed the development of a tomato that can grow in water about a third as salty as sea water.
The work was done by Dr Eduardo Blumwald and Dr HongXia Zhang at the University of Toronto. They describe their efforts in the current issue of Nature Biotechnology.
Irrigation is an essential practice in many arid regions where rainfall is low or where the rain does not come during the growing season. Soluble salts such as sodium, calcium, magnesium, potassium, sulphate and chloride carried by the water are deposited in the soil and can build up over time. This decreases the vigour and productivity of any crop grown in these soils and can render once productive land useless.
The salt affects the plant's ability to take in water and if concentrations are high it can even draw water out of the plant. To counter this the researchers took a gene from the Arabidopsis plant, a relative of the cabbage plant that has become very important in plant research. It was one of the first plants to have its entire genome defined.
The gene produces a substance called a "transport protein", which works inside the plant cells to isolate sodium ions. The salt ions are deposited in vacuoles inside the cell, taking them out of circulation and allowing normal plant biochemistry to proceed.
The salt-storing activity takes place in the leaves and not the fruit, so the tomatoes do not taste salty themselves, according to the researchers who sampled the fruit. This opens up the possibility of using the plants not just in salt damaged soils but also as a way to get the salt back out of the ground and so reverse the damage.
"Since environmental stress due to salinity is one of the most serious factors limiting the productivity of crops, this innovation will have significant implications for agriculture worldwide," stated Dr Blumwald, who led the research. He has since moved to the University of California, Davis, where he will continue the work.
If the technique can be applied to tomatoes then perhaps it will work on other crops, and both universities are continuing efforts to extend salt tolerance to new varieties.
The research is important given the continued growth in world population which over the next 30 years is expected to require an increase in food production of 20 per cent in developed countries and 60 per cent in developing countries.