SUMMARY Tolerance to maize streak virus (MSV) was found and rapidly incorporated into high yielding maize populations for the tropics. Methods were developed for vector propagation and rapid accurate screening of many accessions for virus tolerance in large screenhouses. Tolerance was found in only two accessions and at low frequencies. Further refinements enabled field evaluation for virus tolerance to be combined with high agronomic performance. The tolerance found is simply inherited and was fixed rapidly in breeding. Non‐strain specific tolerance was sought by collecting vectors and different indigenous host grasses from a wide area. The tolerance developed was sufficiently high hardly to affect yield of infected plants. It provided epidemiological or field resistance by reducing disease incidence to insignificance under natural conditions. This tolerance and field resistance has proved effective in several countries of East, West and southern Africa. Varieties derived from this work are now being promoted in Nigeria, and they have potential application elsewhere in the lowland tropics.

No abstract