Breakthrough Introduction of a gene called PSTOL1, which stands for phosphorus starvation tolerance, into modern rice varieties is expected to raise productivity under low-phosphorus conditions. The first generation of rice plants with this gene are under trial in Manila, reports Kalyan Ray
A gene found in a traditional Indian rice variety holds the key to the vital problem of rice productivity, particularly in the developing world where large tracts of soil are poor and nutrient-deficient. The gene allows rice to grow in phosphorus-deficient conditions by making the crops tolerant to the deficiency. This in turn increases productivity by 20 per cent.
In Asia where rice is the main and sometimes the only source of calories, close to 40 per cent of it is produced in rain-fed systems with little or no water control and frequent occurrence of floods, drought and other natural calamities. In addition, almost 60 per cent of (29 million hectares) of rain-fed lowland rice is produced on poor soil, constrained by a number of abiotic stresses and naturally low in phosphorus, an essential for food crop production.
With lakhs of poor and marginal farmers depending on agriculture as their only source of livelihood, access to phosphorous-based fertilisers is limited. There is a high risk that the situation will be aggravated given that phosphate rock, the source of phosphorus-based fertiliser, is a finite and non-renewable resource.
"Fertiliser costs are very high and problematic for poor farmers. Rock phosphate reserves are limited with estimates suggesting that currently known reserves will last only 300-400 years and about 80 per cent of known reserves are in Morocco, west Sahara, USA and China. Accessing them may have its own set of geopolitical problems," explained Sigrid Heuer, crop researcher at International Rice Research Institute in Manila who led a team that developed the phosphorus starvation tolerant rice using the Indian gene found in Kasalath rice cultivated in eastern India. In problem soils, phosphorus is often locked in the soil and unavailable to plants.
Why PSTOL1 matters...
That's where the gene — PSTOL1, which stands for phosphorus starvation tolerance — comes handy. It helps rice grow a larger, better root system and thereby access more phosphorus. The gene enhances rice yields in crops that normally rely on phosphorus-based fertilisers. It makes crops tolerant to low concentrations of phosphorus, partly by enhancing root growth, which enables plants to acquire more phosphorus and other nutrients. Introduction of this gene into modern rice varieties is expected to enhance productivity under low-phosphorus conditions.
"For many years, we have searched for genes that improve phosphorus uptake. We've known for a long time that the traditional Indian rice variety Kasalath has a set of genes that helps rice grow well in soils low in phosphorus," Heuer said. The findings were published in the August 23 issue of Nature. Kasalath's superior performance under phosphorus deficiency conditions was discovered by Matthias Wissuwa from the Japan International Research Center for Agricultural Sciences almost 15 years back. His team studied a subpopulation of rice plants called "aus" varieties, which originated from nutrient-poor soils in India. "There was a growing awareness that these traditional rice varieties were likely to be rich sources of genes encoding tolerance to abiotic stresses. A genetic screen of multiple rice varieties led to the identification of Kasalath, an "aus" line that is significantly more phosphorus efficient than the varieties currently used for rice production. A genetic analysis determined that several regions of the rice genome are associated with improved phosphorus efficiency," Leon V Kochian from the Cornell University said in an accompanying article in Nature.
The task of identifying the actual gene was quite challenging. The researchers had earlier found that phosphorus uptake genomic region, which has the largest beneficial effect on the plant is located on rice chromosome 12. It was named pup1. Subsequent efforts to identify the specific gene or genes responsible for phosphorus efficiency in the Kasalath strain were complicated because greater phosphorus efficiency can arise from several aspects of plant physiology. Heuer and her colleagues used sophisticated breeding technology and modern genetic tools to analyse various regions of the genome to find the gene finally.
"We have now hit the jackpot and found PSTOL1, the major gene responsible for improved phosphorus uptake and understand how it works," she said. The first generation of rice plants are already under trial in Manila and IRRI is encouraging other Asian countries to test these new rice varieties in their countries.
"Trials have been conducted in Indonesia and the Philippines (IRRI station and Pangil, Laguna). The initial work, including field work, was done in Japan. We only now have some seeds available to send to India and Thailand. Our field data suggest that, on average, we can expect about 20% higher yield in the field. But we need to increase seeds to be able to conduct multi location trials on a larger scale," Heuer told Deccan Herald.
Training
IRRI organised a training workshop last week in which participants from six countries, including India - scientists from Indian Agriculture Research Institute and a Tamil Nadu institute - were trained on breeding phosphorus-efficient rice lines in India.
"In our pot experiments," she added, "when we use soil that is really low in phosphorus, we see yield increases of 60 per cent and more, suggesting it will be very effective in soils low in phosphorus such as in upland rice fields that are not irrigated and where farmers are often very poor."
The discovery also demonstrates the importance of conserving the genetic diversity of traditional crop varieties such as Kasalath. "It highlighs the value that lies in investigating traditional plant varieties for beneficial traits that might have been lost during domestication," said Kochian.