Why do Genetically Engineered Crop Varieties Need More Water?
Prof. C. Kameswara Rao
Foundation for Biotechnology Awareness and Education, Bangalore, India krao@vsnl.com, www.fbae.org, www.fbaeblog.org

The question as to why Genetically Engineered (GE) crops perform worse than their non- GE counterparts in drought was asked in the past, and the issue is raised again a few days ago, by the Network of Concerned Farmers (www.non-gm-farmers.com; http://www.non-gm-farmers.com/news_details.asp?ID=2253).  

Soil, temperature and water, when inappropriate, cause what is called abiotic stress on plants.   Farmers know very well that no crop can be grown without a certain minimal quantity of water, properly distributed over the crop duration.   Crops require more water during the phases of seed germination, flowering, and fruit and seed formation.   Conventional crop plant varieties are a pampered lot and cannot withstand water stress (lack of an adequate quantity of water) for long.   They wilt, often beyond the point of recovery, even when water becomes available subsequently.    Such a situation is called para-wilt, often mistaken for wilt due to pathogens.

Some wild species of plants, such as those growing in the aird regions, can naturally withstand a physical deficiency of water.   Some other species, growing in saline soils or in mangrove conditions, tolerate a physiological lack of water, that is, where water is physically abundant but cannot be utilized by the plants due to high salt content. 

Agricultural scientists have been successful in isolating genes that provide these species with the ability to withstand a certain degree of water stress and have developed drought tolerant transgenic crops containing these genes.   We have to distinguish between drought tolerant and drought resistant crops, both of which would require much less water than the conventional ones, and no one should expect even such transgenics to flourish under totally dry conditions.   Drought tolerant plants can withstand only a certain degree of water stress and there cannot be a GE technology that will make plants grow without water.   The development of drought tolerant transgenics is still in the early phases and should not be blocked on imaginary and prompted fears. 

Inherent genetic deficiencies, pests, diseases and weeds constitute biotic stress.   High yielding varieties result from a correction of genetic deficiencies, facilitating a better utilization of inputs resulting in a higher productivity.   Dwarf varieties of rice and wheat have a reduced vegetative phase, both in volume and time, facilitating an enhanced availability of inputs for the reproductive phase resulting in a higher yield.   Dwarf stature also prevents lodging of the crop that causes produce losses.   A high yielding variety requires more water than its counterpart as there is a lot more of vegetative and reproductive growth, that is greater height of plants, more branches and leaves, more flowers, fruits and seeds, called in its entirety, the biomass.  

That improved varieties require more water than their counterparts is not a new issue, only that it was not consciously noticed or projected as a negative feature earlier.   Now it has become handy whip to beat agricultural biotechnology.

Higher water requirement becomes imperative when we prevent damage caused by pests and diseases, either by conventional methods or transgenics.   A healthy plant has a greater biomass and demands more inputs.  Conventional methods of cotton pest control were not very efficient for several reasons.   When the most important pest of cotton, the American bollworm is controlled in Bt varieties, there is more biomass, which naturally requires more water.   Similarly, when we remove the weeds from a crop field, either manually or through herbicides, a severe competition for water and other resources is removed and the resultant increase in biomass needs more water.  

Both abiotic and biotic stresses hamper the expression of a crop variety’s full genetic potential.   The differences in biomass between conventional and improved varieties are very obvious when one looks at, in neighbouring fields, rain-fed and irrigated crop of the same variety or conventional and improved varieties of the same crop.   Transgenic varieties also mature earlier than their counterparts, as could be seen with Bt and non-Bt varieties.  

The need for additional quantities of water on reducing biotic stress is naturally more conspicuously manifested in drought conditions, with added abiotic stress, as there is not only less water available but also there is more than usual loss of water through evaporation from the soil and plant surfaces, into the drier environment.

The remedy is in choosing a crop that is right for the abiotic conditions available in a particular year/crop season.   This means that one cannot grow a choice crop or an improved variety, either all the years continuously or in all the places.    Meteorologists and agricultural scientists should jointly guide such choices.  

July 8, 2005