The Hindu : Drought-resistant rice could be a boon

Online edition of India's National Newspaper
Tuesday, Nov 26, 2002

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Drought-resistant rice could be a boon

By N. Gopal Raj

THIRUVANANTHAPURAM Nov. 25. A team of scientists, led by researchers at Cornell University, U.S. have created a genetically-modified rice that is drought and salinity resistant, major problems facing rice cultivation in India.

Various approaches are being tried in an effort to make crops more tolerant of "abiotic stress", such as drought, salinity and extreme temperature. These factors lower crop yields and increase the uncertainties of farming, especially for poor farmers in developing countries unable to afford irrigation and other remedial measures.

Ray J. Wu's laboratory at Cornell's College of Agriculture and Life Sciences has been looking at the beneficial effects of trehalose, a sugar-like substance shown to stabilise dehydrated enzymes, proteins and cell membranes. Although many plants possess genes for trehalose synthesis, most plant species, except highly drought-tolerant ones which grow in the desert, do not produce detectable amounts of trehalose. In bacteria and yeast, trehalose synthesis is a two-step process. Efforts to introduce the genes for these two enzymes into plants resulted in stunted growth and other undesirable characteristics. Prof. Wu and his group have combined the two genes taken from a bacterium into a single one that produces a fusion enzyme catalysing both reactions.

In addition, the activity of the fusion gene is so controlled that the enzyme is produced only when the plant is under stress or else is carried into the chloroplast, the organelle in the plant responsible for photosynthesis and which is quickly affected by abiotic stress. The scientists opted to genetically modify pusa basmati, an indica rice variety. Even though the genetic transformation process was more difficult in indica than in japonica varieties, the former was chosen because 80 per cent of the rice grown in the world came from indica varieties, they pointed out in the PNAS paper. All rice varieties grown in India are of the indica type.

Faced with prolonged exposure to salt stress, almost all transgenic rice plants survived and displayed vigorous growth. By contrast, all the non-genetically modified plants were either dead or nearly so under the same conditions. Similarly, faced with drought, the genetically-modified lines fared far better. Two lines in particular showed near normal growth when watering was resumed. In addition, the scientists found that the transgenic rice had increased photosynthetic capacity even under non-stress conditions. Improved photosynthesis under abiotic stress conditions was known to limit damage and permit continued growth, they pointed out.

The technology was now mature enough to be tested on a large scale to assess benefits, especially yield under adverse conditions, and also any potential liabilities, said Ajay Garg, the first author of the paper and who did his doctoral research at the Directorate of Rice Research, in Hyderabad, before going as a research associate at Cornell. Compared with other methods being tried to genetically modify crops for abiotic stress tolerance, the trehalose-enhancement technique produced transgenic plants with better growth performance under stress, he told The Hindu.

Although Cornell scientists were seeking patent protection for the technology, this was being done not to control the market and profit from the work but to ensure that the technologies could be offered in the public domain, said Prof. Wu.

About 55 per cent of the rice growing areas in the country were dependent on rain, and drought was often a problem in these regions, E.A. Siddiq, formerly with the Directorate of Rice Research and now a distinguished professor with the Centre for DNA Fingerprinting and Diagnostics, observed. Some seven to eight million hectares of paddy growing land was affected by salinity and the problem was growing as a result of poor drainage in irrigated areas.

If trehalose-enhancement proved beneficial, then the genetically-modified pusa basmati lines could be used as a "bridge parent" to transfer the necessary genes by conventional breeding methods to other indica varieties where such genetic modification was difficult. As only traditional basmati varieties were accepted as true Basmati and were a high-value export product, GM basmati lines should not be released for commercial cultivation, he added.

The Cornell scientists have demonstrated a useful, new gene which could be introduced by genetic modification into plants, observed Akhilesh K. Tyagi of the University of Delhi South Campus. But field trials were needed to assess the yields such GM plants would give, he said. Prof. Tyagi's group has recently reported that introduction of the bacterial gene for choline oxidase (codA) into rice made them salt-tolerant. The codA gene was known to confer tolerance to other abiotic stresses too, he added.

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