Weeds as Part of Agrobiodiversity

Weeds are part of agrobiodiversity, but they have not usually been considered as plant genetic resources for food and agriculture. Plant genetic resources primarily include crop plants and their wild relatives. But as both crops and weeds have been subjected to the influence of domestication and have co-evolved over a long period of time, they provide a largely untapped reservoir of genetic diversity. Some weed species are utilized plants and some are preadapted to become cultivated plants. They are indicators for biodiversity. They are useful for studying the parallel effects of domestication in cultivated plants, and weeds and their evolution. Several weed species are indicators of the autochthonous (original/native) landraces of crops they accompany. Collections of weeds are also basic material for weed control research. Several weeds with a great similarity to crop plants, so-called convergent weeds, are in danger of becoming extinct, due to the intensification of agriculture and improved methods of seed cleaning (eg Agrostemma githago, Bromus secalinus, Lolium temulentum). Examples of the utilization and conservation of weeds are discussed. Ex situ preservation must also be linked with the reintroduction of weed species into agroecosystems (ie maintenance in situ), so that genetic diversity forms part of actively functioning and continually evolving ecosystems. Thus, it is not right to consider weeds only as crop concurrences as is usually done in an agricultural context.