RESPONSE TO SELECTION FOR TOLERANCE TO ACID SOILS IN A TROPICAL MAIZEPOPULATION

Soil acidity reduces maize (Zea mays L.) yields on about eight million hectares in developing countries. We report on response to selection for tolerance to soil acidity, using an altered version of modified ea r-to-row (MER) and full-sib (FS) selection. In the MER selection, 120 half-sib (HS) families were evaluated under 45 and 80% Al saturation. One to three ears from each of the best 30% of the families were selec ted each cycle. After 16 cycles of MER selection, FS selection was ini tiated. Two hundred and fifty FS families were evaluated at rive to si x acid (ASEs) and one normal soil environments (NSE) and the best 25% were selected each cycle. Cycles 2, 4, 6, 8, 10, 12, and 14 of MER and 0, 1, and 2 of FS selection were evaluated in three to nine replicati ons at six ASEs and five NSEs during 1990-1991. Across the 11 environm ents, gain from selection in yield averaged 40 kg ha-1 cycle-1 (1.49* %) with MER and 250 kg ha-1 cycle-1 (8.10%) with FS selection. Across the six ASEs, yield improvements of 40 kg ha-1 cycle-1 (1.99*%) with MER and 310 kg ha-1 cycle-1 (13.%*%) with FS selection were obtained . Yield also improved across the five NSEs by 50 kg ha-1 cycle-1 (1.10 *%) with MER and 150 kg ha-1 cycle-1 (3.31%) with FS selection. Resul ts indicate that tolerance to soil acidity can be improved with recurr ent selection and that the progress will be higher with a system more efficient at reducing the experimental error and genotype x environmen t interaction.