Miracle or menace? : biotechnology and the third world / by Robert Walgate.

  • Walgate, Robert
Date:
[1990]
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Miracle or menace? : biotechnology and the third world / by Robert Walgate. Source: Wellcome Collection.

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    50 Miracle or menaceì related to the African mosaic virus [12]. Rice tungro virus is also a top priority for control, say the St Louis scientists. It causes tremendous yield losses — 40-60% in affected fields, they say. It leads to yellow or orange discoloration, stunting, delayed flowering, and the formation of cancerous growths in severe cases. The St Louis scientists are working on introducing coat-protein induced resistance into rice. Natural resistance to rice tungro is mostly due to resistance to the plant-hopper insects which transmit the disease from plant to plant. This has been bred into good rice strains, but it lasts only 4-5 years in the field as the insects adapt, says rice breeder Gurdev Khush of IRRI. According to Roger Hull of the John Innes Institute in Norwich, UK, the resistance of Green Revolution rice variety IR64 to green leaf-hopper, a vector of rice tungro, has already broken down. The loss of rice from tungro can be estimated at about US$1.5 billion a year, he says. However, rice tungro virus is in fact not one virus, but two: one spherical and the other rod-shaped [13]. The spherical virus is the transmission agent, helping the viruses to get from plant to plant via its leaf-hopper insect vector; the rod-shaped virus causes the symptoms. Work at both St Louis and John Innes now aims to transfer the coat-protein gene of one or other of these viruses into rice. The use of virus-resistant rice varieties in the Philippines could double or triple production, but new rice technology might find its first applications in industrialised countries, social scientists have warned. Coat-protein gene resistance is also one of the few strategies available against the bunchy-top virus of bananas and plantains, which causes major losses in Asia and parts of Africa, as no natural source of resistance has yet been found. A more speculative idea for resisting virus diseases is that of satellite RNA-induced resistance [14]. Some viruses possess separate satellite RNAs that seem to reduce the damage done by the virus and slow its spread through the plant. If satellite DNA could be permanently engineered into the plant, it might have the same effect. DNA copies of satellite RNAs can be transferred into a plant's DNA, where they are translated into RNA. This behaves like natural- satellite RNA, depressing the effects of viral attack. The concept has already been proved experimentally against cauliflower mosaic virus in tobacco. However, in some conditions, satellite RNA actually increases the virulence of a virus attack, so many scientists counsel against its widespread use until the process is better understood.
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