Using CWR to improve crops is more difficult than using other cultivated varieties. Although CWR are related to domesticated crops, they’re not that closely related. In most cases they are a completely different species. Plants from different species are more difficult to mate in a way that results in viable progeny than plants from the same species. Think of mules. Plus, they have many undesirable traits along with the few desirable ones you want, and these must be eliminated during the breeding process.
For example, Oryza nivara was crossed with three domesticated rice varieties to obtain offspring that were resistant to GSV. Breeders had to cross this first generation with the domesticated parent three additional times to obtain resistant varieties that gave as much yield as the original cultivated rice variety.[i] These breeding efforts led to the release of the first GSV-resistant varieties: IR28, IR29, and IR30.[ii] By 1988, rice varieties containing the wild resistance gene were grown on more 30 million hectares in over 30 countries, benefiting millions of people.[iii],[iv]