CWR Species

Crop wild relatives (CWR) are taxa closely related to species of direct socio-economic importance (including food, fodder and forage crops, medicinal plants, condiments, ornamental and forestry species, as well as plants used for industrial purposes, such as oils and fibres), which can contribute beneficial traits, such as pest or disease resistance and yield improvement. A formal definition of a CWR has been proposed by Maxted et al. (2006):

"A crop wild relative is a wild plant taxon that has an indirect use derived from its relatively close genetic relationship to a crop; this relationship is defined in terms of the CWR belonging to gene pools 1 or 2, or taxon groups 1 to 4 of the crop."

Generally speaking, CWR contain the progenitors of our present day crops. After domestication started some 10 000 years ago, wild relatives were utilized to contribute genetic traits to enable crops to adapt to diverse environments and confer resistance to pests and diseases. These same species continue today to contribute to modern varieties of crops such as wheat, maize, rice, potato, cassava, legumes and many others. Thus, the value of CWR has long been recognized; for example, resistance to grassy stunt virus in rice was obtained from a single accession of Oryza nivara, Indian wild rice, which grows from India and Bangladesh to Cambodia, China, Malaysia and Vietnam, which has resulted in the production of new resistant varieties (Khush et al., 1997).  Other improvements obtained through genetic transfer from wild relatives include drought and salt tolerance, early ripening and increased nutritional values, such as protein and vitamin content.  The economic returns from investment in CWR can be striking; for example, genetic material from a tomato wild relative has allowed plant breeders to boost the level of solids in commercial varieties by 2.4 per cent, which is worth $250 million annually to processors in California alone (Poysa, 1993).

Older, more genetically heterogeneous crop cultivars which often contain diverse forms of resistance to pests, diseases and abiotic stresses are increasingly being replaced by modern, advanced, more genetically uniform cultivars in which such diversity of traits have been lost.  The dependence of modern agriculture on relatively few advanced cultivars carries considerable risks: while these cultivars may be more productive in most environments than traditional cultivars, growing a narrower range of cultivars with a narrow genetic basis over larger areas can increase the vulnerability of production systems to changes in climate, land use and disturbance regime, and exposure to biotic stresses, including new races of pathogens. In addition, advanced cultivars may become less effective over time and are often of short duration, needing to be replaced at regular intervals.  For example, in Australia, cultivars of canola (Brassica napus var. napus) with resistance to the fungal disease blackleg (Leptosphaeria maculans) are continually being upgraded—few modern cultivars are used for longer than five years (Li et al. 2006).  The loss of older cultivars and farmers’ landraces has been dramatic in many plant groups and continues to the present day, reinforcing the need for access to wild relatives with the appropriate genetic characteristics for the development of new resistant cultivars.

CWR genetic diversity may therefore be used to develop new or improved varieties that are constantly needed to allow crops to grow successfully in a range of conditions and meet evolving consumer demands. An increasingly important dimension affecting world agriculture is the effects of changes which are a result of human activities and changes in the human–nature relationship, which can be collectively referred to as ‘global change’.  These will undoubtedly lead to an increased demand for the development of new cultivars adapted to these changing conditions, such as raised temperature and lower rainfall levels, and changed agro-environments.  Increasingly, CWR will be looked to as a source of genetic material for breeding these new adapted cultivars. The genes that come from CWR can therefore make a direct contribution to human wellbeing and poverty alleviation, by increasing food production and quality and ensuring long term food security; therefore, the conservation and utilization of CWR is important for the attainment of the Millennium Development Goals. Furthermore, CWR are of major importance as a wild source of nutrition, medicine and other direct uses for many rural communities throughout the world, as well as their general contribution to maintaining ecosystem services.