Rice is certainly one of the most important food crops in the world, in that, nearly half the world's population depends on rice as staple food. It also happens to be the first food crop which has genome sequence readily available, and so from a biotech point of view it is possible to identify the genes in rice that are responsible for productivity, environmental adaptation and resistance to stress.
In the 1980s, tissue culture techniques were adopted for producing better rice varieties. Then Agrobacterium tumefaciens was used to implant foreign DNA in rice plants, which helped not only in improving the genetic make-up of different varieties of rice, but also helped to study the molecular biology of rice.
Biotechnology in modern parlance especially with regard to plants and crops means understanding genetic nuances at the DNA level which is a kind of genetic engineering. This article is about how biotechnology can help in advancing the cause of rice cultivation.
Methods of altering rice crop varieties
There are several ways to alter presently existing rice crop varieties and whichever way is followed, it's ultimately genes that decide how the plant features can be improved. Now, marker-assisted methods can be used to select the wanted genes within a species or in transgenics alien genes can be used to get particular traits. Before molecular markers came on the scene, the evaluation of genetic factors associated with dominant traits was done using biometrical methods.
The advantage with rice is that, since rice whole genome sequence is readily available it can be used to identify genes that are responsible for significant phenotypic variation.
Scientists at the International Rice Research Institute in the Philippines have developed" Super Rice" a high-yielding rice of the future which increases harvests by 25 percent. It is far less bushy as each plant consists of only 10 stems or so in comparison with 20 to 25 of the traditional rice plant. Besides that, a single super rice plant can produce 2,500 grains of rice compared to 1,500 grains from conventional plant.
Repeated use of herbicides in rice fields often leads to the growth of herbicide resistant weeds. There are hundreds of these weeds and especially Oryza rufipogon and Echinochloa crus-galli cause the maximum problems. This means that, the rice farmer has to alternatively use several herbicides or mixtures of different herbicides and there was no guarantee that these herbicides would be harmful to the rice plant as well.
As herbicide tolerance was often due to a single gene, the idea has been to create rice plants with the mammalian P450 enzyme that could detoxify several of these herbicides and make these rice plants tolerant to herbicides. For example, transgenic rice plants with human gene CYP2B6 (a cytochrome P450 monooxygenase that inactivates xenobiotic chemicals) produced rice plants that looked physiologically the same and gave good yields excepting for the fact they had high herbicide tolerance capacity. They could detoxify several herbicides such as thiocarbamates, oxyacetamides and 2, 6-dinitroanilines. To the farmer this is extremely beneficial in terms of labor costs saved.
A specific example is genetically engineered rice that tolerates Liberty herbicide, which has been developed by Aventis CropScience.
Insects are another cause of worry in rice fields. Bt proteins have been successful against some insect varieties but significantly have failed against building resistance to larvae of Scirpophaga incertulans that very much affects Asian rice fields.
To solve this problem of S. incertulans the introduction Bt genes into rice is reckoned as a possibility so that they can produce toxins that combat the insects. Like all proteins, Bt toxins are coded for by genes (stretches of DNA found in the cells) and only a single gene encodes each Bt toxin. Other pests that need to be countered are yellow stem border caterpillar, and Chilo suppressalis (found in temperate areas). So biotechnology helps in avoiding the use of insecticides that harm both the environment and the farmer.
Interestingly transgenic rice plants tolerant to drought and saline conditions have been grown on a pilot plant scale at the laboratory of the late Dr. Ray Wu of Cornell University. This has been done by adding genes into Indica rice varieties (includes basmati rice and majority of rice grown worldwide) to synthesize trehalose, a naturally occurring sugar. Higher quantity of trehalose in rice plants helps the plant counter drought, salinity and extreme weather conditions.
Research is also focused on developing rice plant resistance to rice yellow mottle virus, rice tungro, rice blast and bacterial leaf blight.
Nutrition through rice
Using genetic engineering techniques rice can produce beta-carotene (pro-Vitamin A) in the seed endosperm tissue as for example in Golden Rice (has a gene that produces vitamin A). Although the precise amount of beta-carotene that Golden Rice variety can produce is not clear, the fact remains that it could still be beneficial to millions of people with Vitamin-A deficiency that could possibly lead to blindness. Similarly research is underway to fortify rice with iron using molecular assisted breeding techniques as it could help reduce anemia in women. These efforts are particularly important, as rice being a staple food is the best mechanism to deliver nutrients to the needy, but nevertheless should not be seen as a substitute to an otherwise balanced diet.
Rice milk, rice flour and rice grain cereals, are specially benefited with the emphasis on nutritional fortification of rice
In the long run, biotechnology aims to increase the productivity of rice farming through introduction of transgenic traits and help the developing world prepare adequately for food security. In this regard agronomists use the genetic make up of rice to plan its future evolutionary course.
Although advances in plant genetic engineering may offer even better opportunities for the rice plant, the pace of development of new technologies in rice farming will depend on how the new traits in the rice will be commercially beneficial to the farming community.
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