Importance of CWR
CWR are defined by their potential ability to contribute beneficial traits for crop improvement (Maxted et al. 2006). They have been used increasingly in plant breeding since the early 20th century—for example, to confer resistance to pests and diseases, improve tolerance to environmental conditions such as extreme temperatures, drought and flooding and to improve nutrition, flavour, colour, texture and handling qualities (see Hajjar and Hodgkin 2007, Maxted and Kell 2009 for reviews). CWR diversity thus constitutes an important plant genetic resource for food and agriculture that is available for utilization by national, regional and international stakeholders, and which forms the basis of food and livelihood security (Maxted et al. 2011). In addition, like any other wild species, CWR are also components of natural and semi-natural ecosystems, and also play a role in ecosystem functioning and in broader environmental sustainability and the maintenance of ecosystem services.
Why should we utilize more and more CWR diversity?
- If crops are to increase production levels there is a need for new trait diversity outside that which has been historically used by farmers and plant breeders—CWR offer the necessary, novel genetic diversity that can enhance crop productivity or commodity improvement, promote disease and pest resistance and increase tolerance of adverse or marginal environments.
- Globally, agriculture is being practised in more adverse or marginal environments, whether due to human degradation of habitats or the demand for food forcing the expansion of agricultural lands—the desired traits to grow crops in these environments are found in CWR diversity.
- There is a continuous and growing demand from breeders for novel diversity to be used in the development of new varieties due to the relatively short-term commercial lifespan of modern cultivars (usually 5–10 years).
- Conventional and biotechnological breeding techniques have improved dramatically in recent years enabling more precise targeting of desirable traits, relatively easy transfer to the crop and fewer problems with the transfer of unwanted characteristics from exotic CWR material.
- The conservation of CWR in existing protected areas offers an additional ecosystem service to the protected areas themselves, so for limited additional resource commitment the perceived value of the protected areas can be significantly enhanced.
How can current crop varieties cope with changing environments?
While climate change will directly impact CWR diversity, it will also alter the agro-environmental conditions under which our crops grow and will augment the risk of pest and disease spread, thus impacting agricultural production. It is likely that many current crop varieties will need replacement to enable them to better suit the new and changing agro-environments (e.g. Jones et al. 2003, Duveiller et al. 2007, Deryng et al. 2011, Li et al. 2011, Luck et al. 2011). Failure to meet this challenge could have a devastating impact on the global economy and social well-being. Genetic diversity offers an insurance against the harmful impacts of climate change, and CWR are particularly likely to contain the breadth of genetic diversity necessary to combat these impacts because of the diversity of habitats in which they grow and the wide range of conditions to which they are adapted (FAO 2008). Nevertheless, climatic change can lead to non‐analogous climate conditions and their consequences are thus difficult to predict. Therefore, CWR diversity is under threat from climate change, while at the same time they offer a critical means of mitigating the predicted impact of changes in climate.
Use of CWR diversity in crop improvement
Use of CWR diversity in crop improvement
The increasing human population and periodic food shortages have led to raised awareness of the need for global and sub-global food security. In turn, this has stimulated the search for genetic material that can be used to enhance crop productivity, disease resistance, and tolerance to various environmental conditions, for which CWR are potential sources (Heywood 1997). As a consequence, there is a growing demand for the development of novel varieties adapted to the new environmental conditions that have rapidly ‘evolved’ in recent years, as well as to meet the short‐term adaptation goal of breeding new varieties that address changing consumer demands (Heywood et al. 2007). Additionally, inter- and intra-species crossing techniques have rapidly developed, facilitating the use of CWR diversity in the improvement and creation of new varieties.
CWR thus present a tangible resource of actual or potential economic benefit for humankind at national, regional and global levels. Exploitation of its diversity has existed for millennia, with farmers using variation within and between species to improve their crops from the beginnings of agriculture. For example, subsistence farmers in Mexico would annually grow cultivated corn near its wild relatives to facilitate introgression between the CWR and the crop as a means of crop enhancement (Hoyt 1988). These species and this process are as important to humankind today as they were to the earliest farmers. Developments in the biotechnology industries are now allowing more precise transfer of genes, even in the case of CWR from more distantly related species, further enhancing the value of CWR.
Tanksley and McCouch (1997) and Hajjar and Hodgkin (2007) argued that breeders were not fully exploiting the potential of CWR. Historically, breeders relied on searching for specific beneficial traits associated with particular CWR taxa rather than searching more generally for beneficial genes. They also avoided transfer into polyploid crops where transfer was more difficult (e.g. rice, sorghum and sweet potato). The use of CWR diversity in crop improvement programmes for 29 major crops has been reviewed by Maxted and Kell (2009), who reported that for these crops there are 234 references that report the identification of useful traits in 183 CWR taxa (see Figure below). The review showed that the degree to which breeders use CWR varies between crops, with CWR use being particularly prominent in barley, cassava, potato, rice, tomato and wheat improvement. Rice and wheat are the two crops for which CWR have been most widely used, both in terms of number of CWR taxa used and successful attempts to introgress traits from the CWR to the crop. The number of publications detailing the use of CWR in breeding has increased gradually over time—presumably as a result of technological developments for trait transfer—with 2% of citations recorded prior to 1970, 13% in the 1970s, 15% in the 1980s, 32% in the 1990s and 38% after 1999. The most widespread CWR use has been, and remains in, the development of disease and pest resistance, with the references citing disease resistance objectives accounting for 39%, pest and disease resistance 17%, abiotic stress 13%, yield increase 10%, cytoplasmic male sterility and fertility restorers 4%, quality improvers 11% and husbandry improvement 6% of the reported inter-specific trait transfers. It can also be seen from this review that since the year 2000 the number of attempts to improve quality, husbandry and end-product commodities has increased substantially. However, the exploitation of the potential diversity contained in CWR appears to be hit and miss as the approach by breeders to CWR use has not been systematic or comprehensive; therefore, the vast majority of CWR diversity remains untapped for utilization.
What is the monetary value of CWR?
What is the monetary value of CWR?
The particular food security value of CWR has been recognized at least since Darwin discussed their study and conservation (Darwin 1868), but it was Vavilov (1926) who was the first to promote their systematic conservation in practical terms. However, CWR conservation have remained widely neglected because the responsibility for their conservation has neither been adopted by agricultural agencies (whose remit is not wild species conservation) nor environment agencies (whose focus is not on PGRFA conservation). It is only relatively recently that their systematic conservation has been addressed due to the growing interest in their use as gene donors (e.g. Maxted et al. 1997a, Meilleur and Hodgkin 2004, Heywood and Dulloo 2005, Stolton et al. 2006, Maxted et al. 2008a), even though their value as gene donors has been extensively documented since the 1970s (e.g. Frankel 1970, Jain 1975, Prescott-Allen and Prescott-Allen 1986, Hoyt 1988). Their economic value is now understood. For example, it has been estimated that approximately 30% of modern crop production increase is due to the use of CWR genetic diversity and that this has an annual value of approximately US $115 billion worldwide (Pimentel et al. 1997). As an example, in the 1970s the US maize crop was severely threatened by corn blight which destroyed almost US $1,000 million worth of maize and reduced yields by as much as 50% in 1978 (FAO 2005). Blight resistant genes from Mexican maize CWR were used to solve this problem (Prance 1997).
A recent study commissioned by the Millennium Seed Bank Partnership, Kew (MSB), and carried out by PricewaterhouseCoopers (PwC), UK, has estimated that the wild relatives of 29 crops prioritized by the MSB have a value of $42 billion, with a potential of $120 billion in the future in terms of their potential for improving productivity or stress resistance in commercial crops (PwC 2013). If maize, soya bean and sugarcane are included, the current and potential values increase to $68 billion and $196 billion, respectively. These results were based on analyses from seed development to farmgate sales of four crops (wheat, rice, potato, and cassava) and extrapolated to the target 29 crops.
The Interactive Toolkit for Crop Wild Relative Conservation Planning was developed within the framework of the SADC CWR project www.cropwildrelatives.org/sadc-cwr-project (2014-2016),
which was co-funded by the European Union and implemented through ACP-EU Co-operation Programme in Science and Technology (S&T II) by the African, Caribbean and Pacific (ACP) Group of States.
Grant agreement no FED/2013/330-210.