Select Committee on European Communities Minutes of Evidence


Review of Virus-resistant plants: potential ecological impact, edited by M Tepfer and E Balâzs, published in New Phytologist

  "Only the foolhardy will have firm views on the likely outcome of the introduction of virus-resistant transgenes into agriculture" say Gibbs, Armstrong, Weiller and Gibbs in the first chapter. Virus diseases of plants cause serious losses all over the world, so it is not surprising that transgenic virus resistant plants are, or about to be, in commercial use in many places including China, India and the US, sometimes with multiple resistances.

  Transgenic plants expressing virus proteins can be resistant to infection by that virus. That means that one or more virus genes, often coat protein genes, have been incorporated into the plant's genome. Virus resistance can also be achieved by incorporating benign satellite RNAs. Will recombination and transcapsidation produce undesirable ecological effects? The principal impacts of concern are altered host ranges, altered symptoms, synergistic effects between different viruses, altered modes of transmission. Synergism, where unrelated viruses interact to increase the titre of one or both, is a particular case of the worry that transgenes may produce a favourable environment for change. Altered host ranges includes spreading to related (wild or cultivated) species.

  This book "evolved from" a conference in April 1997 (in Hungary) organised by the Directorate for Agriculture of OECD. There are 15 chapters by 47 authors from 10 countries, so it is truly international. The chapters are not numbered in the text, though they are in the contents list, and the indexes are only of plants and viruses, not of topics or authors. All that makes cross-referencing difficult, but a systematic summary in the last chapter by the two editors is helpful. Far more of the book is concerned with the molecular biology of virus resistance than with directly assessing the potential impact, let alone the ecological impact promised in the title.

  To what extent are there likely to be real risks from virus resistant plants? The conference agreed that these should be assessed against the risks that occur naturally, and recombination and transcapsidation do. Very little is known about the frequency of either and still less about the extent to which these processes will be changed in transgenics. There will be lots of optimistic risk assessments with the standard line "There is no evidence that . . . ". With commercial lines in places where risk assessments are not taken seriously, we could soon have real evidence if it is looked for and reported. Monitoring is expensive, discouraging reports are discouraged, as we know only too well from BSE.

  Still, there are many indicators here that transgenic virus resistant plants may well enhance the natural risk producing processes. "Three of seven recombinant [with a transgene] cause symptoms on cowpeas that were distinct" (Allison, Greene & Schneider). "Transgenic plants expressing viral sequences create a favourable environment of recombination between viral sequences" and "there is a high selection pressure for recombination in transgenic plants" (Jakab, Vaistij, Droz & Malnoe). "In some cases these risks [from synergism] are much higher than would occur if pathogen-derived resistance was used instead" (Palukaitis & Kaplan). And so on.

  Despite the lack of information on rates, sequencing has shown that virus evolution has been polyphyletic and reticulate, dominated by recombination. Processes important in evolution, acting slowly, could become much faster in transgenic plants, and there is much opportunity for real ecological innovation. What I doubt is whether, world wide, we have either the inclination or means to anticipate it. But this book does at least show that informative experiments are possible, that risk assessment is much trickier here than with other transgenic constructs, and that there are people at the international level taking the problems seriously.



 
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