In the early 1970s, outbreaks of a disease called grassy stunt virus (GSV) destroyed more than 116,000 hectares of rice fields in Asia.[i] Grassy stunt virus, which is transmitted by the brown plant hopper, causes rice plants to produce deformed grains, or no grains at all. Epidemics of grassy stunt virus can lead to substantial reductions in yield, or even cause the total loss of a harvest. The Economist estimates that the grassy stunt virus caused damages costing over $300 million – worth more than $1 billion in 2015 dollars. [ii]
When scientists at the International Rice Research Institute screened 6723 different types of cultivated and wild rice for resistance to the virus, only one was found not to be affected: accession number 101508, a sample of the wild species Oryza nivara. Breeding using this particular wild population eventually led to the development of improved rice varieties with resistance to GSV. These were released in many countries in Asia, helping thousands of farmers combat the disease and avoid big losses in production.[iii]
At the very least, crop wild relatives contain genes for a multitude of useful traits that, if transferred to crop varieties, can provide substantial economic value by boosting yields, expanding cultivation into marginal land, and increasing the input efficiency of agricultural production. But they also have the potential to avert disaster, as seen in the example above. Wild potato species contain genes for resistance to late blight, the disease that destroyed large portions of the Irish potato harvest in the 1840s and helped to trigger the Irish Potato Famine. [iv] The devastation of vineyards across Europe caused by the aphid-like insect phylloxera was finally stopped by the use of rootstocks from wild American grape species. [v] And wild bananas may also provide the key to breeding a banana variety resistant to Black Sigatoka, a rapidly-spreading fungus that is lowering banana yields across the world. [vi]
Crop wild relatives provide the opportunity to improve the productivity and resilience of agriculture. However, in the coming century, as population increases to over 9 billion and climate change intensifies, exacerbating the spread of crop pests and diseases, they may become indispensable.