Gene flow between crops and their wild relatives

Gene flow from domesticated plants to free-growing relatives was a rather trivial issue before the advent of transgenic crops. Gene flow into crops was relatively more important, especially to plant breeders trying to introduce new genes in a crop, or to breeders and seed growers wanting to ensure the genetic purity of a cultivar. Genes can now be transferred from bacteria, or potentially any plant or animal species into crops and so, crop to weed gene flow is not so trivial anymore. What if these transgenes can persist in the environment? Anyone interested in this biosafety issue will soon realize that potential gene flow from crops is highly variable depending on the crop species and the presence of wild relatives where the crop is currently cultivated. While information on specific crops abounds, especially in scientific journals, most reviews that include multiple crops are published as regulatory reports and focus on crops grown in developed countries. The main objective of this book was to compile information on relationships between cultivated crops and their wild relatives in order to promote the conservation and utilization of crop genetic resources. Therefore, crops uncommon in developed countries but grown in areas of high biodiversity are included. Andersson and de Vicente, have worked and collaborated with multiple institutions and scientists around the world (Costa Rica, Germany, Colombia, USA and Italy, to name a few) to write this review. It is a good reference source, especially for regulators and policymakers, but also of interest to breeders, plant evolutionists, ecologists, conservationists, agronomists and botanists. The book allows the rapid assessment of gene flow potential by crop (each chapter from 2 to 22 focuses on a single crop) and by geographical location (world maps are presented at the end of the book). Each crop is introduced with a nice picture of its inflorescence. Chapters are in alphabetical order according to crop common name. Crop names are also found at the bottom right of odd pages, providing a simple index that allows rapid consultation. Chapter one outlines the importance of crop diversity and gene flow, as more and more genetically modified (GM) crops are planted. The authors define terms such as: gene flow, hybridization, introgression and ecological effects of introgression. Chapter two essentially describes the methodology for selecting and gathering the information. The method used for the modeled likelihood of introgression for each crop (the innovative world maps) is described with more details on pages 549–560. Subsequent chapters each focus on a single crop selected according to three criteria (i) world production area, (ii) advances in GM technology and (iii) relative contribution to food security. For each crop, the number of domesticated species is mentioned along with the reason for selecting one or two species. The center(s) of origin and diversity are listed, followed by information on flowering, pollen biology, reproduction, seed dispersal and dormancy, persistence, weediness/invasiveness, crop wild relatives (also listed in a Table) and hybridization. Finally, there is information on bridge species, pollen flow (sometimes illustrated as a figure presenting outcrossing as a function of distance), isolation distances, state of the GM technology for the crop, agronomic management recommendations to minimize gene flow, crop production area, research gaps and conclusions. The first chapter provides a good introduction to the subject although some statements are over simplistic. For example, stating that ‘seed dormancy of some GM canola is significantly higher than non-GM controls under some field conditions (Linder. 1998. Ecological Applications 8:1180–1195)’ without mentioning that the GM trait modifies oil composition, is misleading. Oil composition can potentially alter seed dormancy since seed oils are sources of energy prior to the initiation of photosynthesis (in Linder and Smith. 1995. Ecological Applications 5:1056–1068, in the references). I wish the method used to rank and select the twenty crops was described or some explanation given as to why sugarcane (Saccharum spp.) [24 million ha (M ha) in 2008], sunflower (Helianthus annuus) (25 M ha in 2008) (http://faostat.fao.org/) or all forage crops were left out in favor of cotton (Gossypium hirsutum and G. barbadense) (33 M ha, advances in GM technology, but how much does it contribute to food security?), pigeon peas (Cajanus cajan) (4.6 M ha, no commercial GM production) or finger millet (Eleusine coracana) (4 M ha, no transformation protocols). I salute the inclusion of food crops produced essentially in India (pigeon peas) and Africa (finger millet), but expected to find sugarcane or alfalfa (Medicago sativa). Perhaps it should have been specified Evolutionary Applications ISSN 1752-4571