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IV. Drought and Salinity tolerance and GM crops

12. Dr. John Passioura, CSIRO, Australia, focused on the key strategies for ensuring efficient water use by crops in an agriculture environment. He emphasized that tackling drought was a matter of resource economics and finding strategies for obtaining the best yield under fixed and limited water supply. It required expert water management along with improvement in the genetic make-up of crops. Healthy vigorous plants are best at achieving water-use efficiency. Through several examples, he showed that the genetic make-up of crops could be improved for capturing more water supply for transpiration; increasing exchange of transpired water for CO2 for producing biomass, and for converting more biomass into grain, and raising the harvest index of crops. He stated that, by adjusting flowering time, a right balance could be struck between using water before flowering and in using water after flowering to fill the grain. Therefore, tackling drought required a combination of good agriculture management practices, and a thorough understanding of the strong interactions between genotype and highly variable environments of the crop plants. Due to the complexity of the processes, he pointed out that to date, there have been no big breakthroughs in developing 'drought resistant' GM crops. As there were little prospects of such crops in the near future, he considered it premature to discuss their possible environmental effects.

13. On the issue of 'Salinity tolerance and GM crops', the expert examined the mechanisms applied by plants to tackle salinity, and described the best agricultural practices to deal with salinity related problems. He noted that most plants, including mangroves, (with the exception of lupins and rice) excluded at least 98% of the salt contained in the water that entered the roots, because excess of salt truncates the life of leaves. Plants also sequestered salt, into vacuoles, to prevent damage to the cells metabolic machinery. Halophytes and some crop plants, for example, barley, are effective in this activity. He noted that molecular studies have shown the possibility of single gene-controlled salt transport mechanisms. Although this was valuable information, the expert was not sure how it could lead to the development of salt-tolerant transgenic plants in the foreseeable future. Plants in the fields provide a wide and diverse range of responses to the fluctuating salt concentrations. However, currently used laboratory techniques did not simulate these field situations in real time and therefore, could not be considered plausible working models for studying salinity tolerance in a practical manner. The expert noted that some success had been achieved in tackling drought tolerance and salinity tolerance through conventional methods and through molecular technologies like marker-assisted selection. However, he strongly cautioned against expecting miracles in this sector, at least in the foreseeable future, because of the complexity of the interactions and systems.

During the discussion, many participants did not agree completely with the expert on the unfeasibility of generation of drought or salinity tolerant GM crops. They acknowledged the enormity of the challenge but pointed out that a steady progress was being made and that there was a distinct possibility of release of drought tolerant crop varieties within few years. The key points from the discussion were as follows:

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