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Fitness factors in F1 hybrids
In a recent commentary I discussed the possibility of gene flow from crops, whether GM or conventionally bred, to related wild plants. One of the questions that arises is whether such hybrids may be at a selective advantage, thus allowing the maintenance of particular genetic traits, derived from the crop species, in the wild. Although many crop plants do not have the potential to hybridize with wild relatives, others certainly do. One such is cultivated rice, Oryza sativa, which is well-known to cross with wild rice, O. rufipogon. Song et al. (Fudan University, Shanghai, pp. 311-316) have therefore carried out an extensive investigation of the fitness of the hybrids in relation to both parental species. They point out that a proper evaluation of overall fitness cannot be obtained by assessment at any particular stage of growth or development. Fitness is a lifelong feature and thus the authors compared performances at many stages of the plants’ lives, including germination, seedling survival, various aspects of growth, clonal propagation and sexual reproduction. Morphologically, the hybrids resemble more closely the wild parent; in vegetative growth they performed better than either parent, thus exhibiting hybrid vigour. However, within a single generation grown under normal rice cultivation conditions, there was no significant difference in overall fitness between the three lines. But ultimately fitness involves reproductive success and here the hybrids perform significantly less well than either parent. This suggests that the F1 generation is likely to be a barrier, albeit not a strong one, to the introgression of crop genes into wild populations. Further, the hybrid shows a similar lack of seed dormancy to the crop parent, thus lacking a winter survival mechanism possessed by wild rice. This may explain the failure of O. sativa-O. rufipogon hybrids to become widely established even in areas where hybridizations are relatively frequent.
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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