Past use of CWR in crop improvement

Crop wild relatives have played an often fortuitous and sometimes essential role in improving agricultural systems over the past two centuries, even if their contributions often go unnoticed by the general public.

An early example of the use of CWR took place in the late 1800s, when grape phylloxera (Daktulosphaira vitifoliae) arrived in Europe from North America. The small, aphid-like insect feeds on the roots of grapevines, and the newly arrived species proceeded to do just that all over Europe, but particularly in France, where it led to what became known as the “Great French Wine Blight.” In France alone, an estimated 2.5 million hectares of vineyards were destroyed by the pest between 1868 and 1900.[i] The solution came, ironically enough, from the same place as the problem, in the form of the wild North American grape species Vitis rupestris, Vitis berlandieri, and Vitis riparia, which have phylloxera-resistant roots. These were sent across the Atlantic by American botanists, and European wine-growers began the long task of reconstituting their vineyards with resistant, wild rootstocks. Today, wild Vitis rootstocks can still be found in the vast majority of vineyards around the world, with favorites such as Chardonnay, Merlot, Sauvignon Blanc, Cabernet Sauvignon and Pinot Noir grafted on them.[ii]

If you prefer beer to wine with your dinner, you might be interested to know that some of today’s most prized hop varieties obtained their high alpha acid content from past crosses with two collections of wild hops from North America.[iii]

The rapid spread of sugarcane mosaic virus (SCMV) was the trigger for another early use of CWR species. The virus was only stopped from devastating sugarcane-growing regions, and the industry saved, when new cane varieties were introduced with SCMV-resistance from wild Saccharum spontaneum. The key cross occurred spontaneously, between the cultivar Black Cheribon and some wild S. spontaneum growing on an extinct volcano in Indonesia. Later, in 1921, this would lead to the breeding of sugarcane variety “P.O.J. 2878,” described as “the greatest cane of all.” Without resistance provided from the wild, “there would most probably not now be a viable sugarcane industry anywhere in the world.”[iv]

Sugarcane is not the only crop to satisfy your sweet tooth that benefits from some wildness:– cacao and oil palm have also gained valuable wild genes through targeted breeding efforts. Cacao (Theobroma cacao), the source of chocolate, gained substantial increases in yield and drought tolerance from crosses with wild germplasm from the Upper Amazon, and breeding with wild Elaeis guineensis from central Africa boosted oil palm yields by 25%.

Crop wild relatives have in fact provided many other valuable traits to a great range of crops. Drought tolerance in rice and barley were introduced from wild Oryza longistaminata and Hordeum spontaneum, respectively. Heat tolerance was provided to chickpea by its wild relative, Cicer reticulatum.[v] The wild tomato species Lycopersicon pimpinellifolium has provided resistance to Fusarium oxysporum, which led to the release of Pan America in 1941, the first tomato cultivar resistant to the fungus, and allowed the expansion of tomato production to the sandy soils of Florida.[vi] The table below presents estimates of the annual economic value of genetic material provided by CWR in 1986.

Estimated annual value of genetic contributions provided by CWR to US agriculture in 1986 in 1986 $ and 2012 $.[vii]

Percentage of total Total annual value of contributions (1986 $) Total annual value of contributions (2012 $)
Sugarcane 34.8% $119,400,000 $250,120,000
Sunflower 25.8% $88,500,000 $185,390,000
Cacao 14.3% $49,000,000 $102,650,000
Bread wheat 10.3% $35,300,000 $73,950,000
Oil palm 9.4% $32,300,000 $67,660,000
Hops 3.5% $11,900,000 $24,930,000
Sugar beet 0.9% $3.0 – $3.25 million $6.28 – $6.81 million
Tobacco 0.5% $1,900,000 $3,980,000
Oats 0.4% $0.6 – $2.3 million $1.26 – $4.82 million
Bermuda grass 0.1% $400,000 $837,900
Total1 $342.3 – $344.25 million $717.1 – $721.1 million

 

1Prescott-Allen and Prescott-Allen (1986) also included potato, tomato, bell pepper, strawberry, cotton, tulip, sweet clover, alfalfa, Spanish iris, smooth brome, highbush blueberry, and lettuce as crops which benefited from wild species, but were not able to estimate the value of these contributions.

In addition to the current value of their past contributions, CWR possess a number of traits of great potential value for future breeding efforts. For example, the wild rice species Oryza coarctata is very tolerant to salinity, while the wild barley Hordeum bulbosum is resistant to a number of diseases and in addition is tolerant to drought, salt and frost. Further genes for drought tolerance have also been identified in the wild chickpea species Cicer echinospermum and the wild sunflower species Helianthus argophyllus.[viii] The wild species Lycopersicon hirsutum is a source of resistance for 9 of the 16 major insect pests of the tomato plant.[ix] These contributions are not trivial: a PricewaterhouseCoopers LLP study estimates the potential value of future use of the wild genepools of 32 major crops at $196 billion.[x]