The value of CWR and their utilisation

The use of genes from CWR in crop improvement has been steadily increasing since the 1940s (Hajjar and Hodgkin, 2007; Maxted and Kell, 2009). Maxted and Kell (2009) found that 2% of citations in the literature describing CWR use in plant breeding were published prior to 1970, whereas 38% had been published after 1999. The numbers of citations and examples of the use of CWR relating to 29 global priority crops are illustrated in Fig. 1.3, with results indicating that CWR have predominantly been used to improve staple crops such

as wheat, rice and barley (Maxted and Kell, 2009). This suggests a need to expand research into a wider range of crops and their associated CWR to draw further beneficial traits from their largely untapped gene pools.

Figure 1.3 Total numbers of references that have reported the identification and transfer of beneficial traits from 185 CWR to 29 global priority crops, also showing the number of CWR taxa utilised per crop (Source: Maxted and Kell, 2009).

Their increasing utilisation has prompted many studies to estimate the value of their contributions to improving crop varieties. Pimentel et al. (1997) calculated that CWR contribute $115 billion per year globally to increased crop yield. In America alone, it was calculated that CWR contribute more than US$350 million per year in terms of improvements in yield and quality (Prescott-Allen and Prescott-Allen, 1986). Furthermore, Phillips and Meilleur (1998) estimated that if endangered CWR were to be lost, approximately $10 billion annually in wholesale farm value would be also be lost as a result. A more recent valuation of the potential benefit of using CWR to breed improved commercial crop varieties has been carried out by Price Waterhouse Cooper in collaboration with Kew’s Millennium Seed Bank (MSB). They estimate that the potential value of using CWR to improve MSB’s 29 priority

crops, those listed in Annex I of the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA) (FAO, 2001), will increase from $42 billion in 2013 to $120 billion in 2021 (PwC, 2013). This valuation considers only 29 priority crops rather than CWR as a whole, suggesting that a full valuation of the potential of all globally important CWR to contribute to crop development would be much greater. Though the methods of estimation and valuation differ between studies, it is clear that CWR are a highly valuable genetic resource.

The majority of examples of crop improvement using traits from CWR have focused on pest and disease resistance. Hajjar and Hodgkin (2007) found that of 100 traits bred from a range of 60 wild species into 13 crops, over 80% conferred pest and/or disease resistance. Furthermore, 56% of citations (relating to the use of CWR in 29 priority crops) reviewed by Maxted and Kell (2009) were related to pest or disease resistance traits. For example, a cross, and subsequent backcrosses, between wild wheat relative Aegilops peregrina (Hack.) Maire & Weiller and cultivated wheat Triticum aestivum L. was carried out by Marais et al. (2008). This led to the spontaneous translocation of a segment of a chromosome containing a gene (Lr59) conferring resistance to mixed leaf rust (Puccinia triticina Eriks.) in cultivated wheat. In another example, a dominant gene (Er3) was identified in the wild species Pisum fulvum Sm. that provides resistance to powdery mildew (Erysiphe pisi DC.), a disease that results in severe yield losses in cultivated pea Pisum sativum L. (Fondevilla et al., 2007). Successful hybridisation between these wild and cultivated pea species and the resulting production of plants resistant to powdery mildew demonstrated the potential of using P. fulvum in breeding programmes (Fondevilla et al., 2007).

traits. Lakew et al. (2011) tested the drought tolerance of a range of introgressed lines of barley when exposed to nine environments with variable water availability. These breeding lines originated from a cross between wild Hordeum vulgare L. subsp. spontaneum (K. Koch) Thell. and cultivated barley Hordeum vulgare L., the former known to have a higher capacity to tolerate drought (Grando et al., 2001). The range of responses to the environments to which these barley lines were exposed led Lakew et al. (2011) to conclude that H. vulgare subsp.

spontaneum is likely to be a good source of drought tolerance genes that can be further

investigated and used in barley breeding programmes to produce varieties more resilient to predicted changes in climate. Another key example of a recent success in improving abiotic stress tolerance of a crop using traits from CWR is that of rice. In 2013 the International Rice Research Institute released details of a successful interspecific hybridisation between the CWR Oryza coarctata Roxb. and the cultivated rice variety IR56 of Oryza sativa L., using embryo rescue techniques. O. coarctata is able to tolerate twice the concentration of salt compared to cultivated varieties, and this cross will no doubt have a vast impact on improved yields of cultivated rice once a commercial variety has been developed and released (IRRI, 2013). Taking this research further still, Garg et al. (2014) has sequenced the transcriptome of

O. coarctata and identified 15,158 genes linked to salinity and submergence tolerance. This

vast array of genes found in a single wild relative in relation to a single abiotic stress provides some idea of the range of useful genes and beneficial traits that are yet to be identified and characterised in CWR. Advances in biotechnology such as sequencing and embryo rescue techniques are having a significant impact on plant breeding, particularly in aiding the characterisation of CWR germplasm to find genes of interest and facilitating the use of more distantly related CWR, including those in the tertiary gene pool of a crop (e.g. Lens: Davies et

al., 2007; Alliaceae: Chuda and Adamus, 2009; Cajanus: Mallikarjuna et al., 2011; Vaccinium: Ehlenfeldt and Ballington, 2012; Oryza: Garg et al., 2014).

Above are just a few examples of a vast literature on crop improvement using traits from CWR. Examples of other types of beneficial traits used from CWR include those for improved yield, improved quality, cytoplasmic male sterility, fertility restorers and husbandry improvement (Maxted and Kell, 2009). Ultimately, the value of CWR can be considered in terms of their potential economic contribution to the agricultural industry but also, and perhaps more importantly, the innate value of the pool of genetic diversity and potentially useful traits within CWR that could help to mitigate the impact of climate change or other unforeseen problems facing food production, and that will be lost if these genetic resources are not preserved for the future.