DEVELOPMENT OF SYNTHETIC MAIZE POPULATIONS FOR RESISTANCE TO STRIGA-HERMONTHICA

The parasitic witchweed, Striga hermonthica (Del.) Benth, is the great est biological constraint for cereal crop production by resource-poor farmers in sub-Saharan Africa. Maize, Zea mays L., is a widely grown c ereal crop in this region (22 x 10(6) ha). Striga-resistant maize popu lations were produced and tested as half-sib families in West and Cent ral Africa. Three populations with white (W), yellow (Y), or mixed (Y/ W) grain colour were formed by: (1) intercrossing Striga-resistant mai ze inbred lines followed by two generations of random mating; (2) test ing under artificially induced S. hermonthica infestations in Nigeria, Cameroon, and Ivory Coast and selection of resistant families; (3) tw o generations of random mating; and (4) two years of testing for resis tance. Striga-resistant synthetic W, Y and Y/W populations were produc ed by compositing resistant half-sib families. Outstanding performance in grain yields and host plant resistance was observed. Maize damage ratings and number of harvested ears were highly correlated with grain yield. High variation was observed for Striga emergence counts. The p opulations have combined resistance to Striga, maize streak virus (MSV ), and other major biotic constraints for maize cultivation in Africa, thus providing the opportunity for improved sustainable maize product ion under stress environments. Breeder's seed of these synthetic varie ties are being multiplied for distribution to national programmes.