Molecular biology approaches to control of intractable weeds: New strategies and complements to existing biological practices

Molecular genetic tools and concepts are in relentless and continuous development, affecting every field of biology. Biological control of weeds, an applied science with over a century of history, is no exception. There are many examples of successful biocontrol of weeds, in some cases quite spectacular. However, biocontrol is not applicable to every weed challenge, in large part due to the limitations of available biocontrol agents. Indeed, one cannot realistically expect that naturally occurring agents have serendipitously evolved to meet all of man's weed control needs. In cases where agents are lacking, molecular biology may be able to improve biocontrol, reduce dependence on chemical herbicides, and control intractable weed species. In theory, any biological weed control strategy could be improved through molecular biology, whether by improvement to a biocontrol agent (e.g. increased lethality, improved specificity, ability to work in concert with other pest management tactics), improvement of the crop (e.g. improved weed-inhibiting properties), by increasing knowledge about the evolution of the target and its natural enemies to assist the search for and selection of classical biocontrol agents, or even by genetic manipulation of the target weed itself. Molecular genetic technology can enable novel strategies that would not be possible in its absence, as well as allow weed researchers to adapt molecular solutions from other fields, including biocontrol of other pests or fields only remotely connected to weed biocontrol. This paper will review concepts of weed biocontrol and molecular biology applications to weed control, as well as propose novel weed-control strategies.