Nematode-resistant potato, rice and banana are being developed for subsistence growers. Nematodes cause estimated global losses of 20% to banana, 12% to potato and 10% to rice. Higher values are probable in subsistence agriculture. In Africa, using FAO estimates of yields, losses due to nematodes are likely to exceed 6 million tonnes (m t) for banana, 1.5 m t for potato and 1 m t for rice. In Asia, losses are comparable to Africa for banana, and much higher for rice and for potato (15 m t). A transgenic approach is being used because traditional breeding for nematode resistance is difficult. Transgenic approaches can be faster because breeding is a very long-term process in potato and breeding bananas (a clonal crop) is extremely difficult. The three target crops are all damaged by several different nematode species and each requires a separate and considerable breeding effort. Genetic modification allows the development of plants resistant to a range of nematodes so, for their effective use, growers do not need to know which of these pests are problems. The genetic modification is highly biosafe as it involves transferring genes from maize or rice that express a protein (cystatin). The cystatin is found in the grain so it is already consumed by billions of humans as part of their diet. The cystatin prevents the nematodes from digesting proteins so they are malnourished, develop slowly and reproduce much less.