||The main research activities of the SARMP have continued to be guided towards the development and improvement of maize germplasm with tolerance to aluminum toxic- acid soils. These type of soils are present in approximately 40% of the arable land in tropical countries, with extremely poor soils due to low pH, and either deficiency or toxicity of some micronutrients. The products derived from this research are targeted to develop maize germplasm with tolerance to acid soils and some regional biotic stresses which are limiting factors for maize production in countries in the region, including fall armyworm, phaeosphaeria leaf spot, polysora and physopella rusts, corn stunt, ray ado fino, and sugarcane mosaic virus. The program has developed, and concentrates its activities, in the improvement of 4 genetically broad based populations, including 2 heterotic populations with yellow (SA3 and SA4) and 2 heterotic populations with white (SA6 and SA7) endosperm. Inbred lines, open pollinated varieties, synthetics, and hybrids have been generated from these four base populations, and their products tested by interested collaborating programs. The above four base acid soil-tolerant populations are being improved following a reciprocal recurrent selection scheme. Germplasm is improved by testing and selecting tolerant germplasm in nurseries established at Villavicencio, Menegua, and Palmira, in Colombia, and collaborating countries in South America. Germplasm generated from these populations is offered to NARS to be evaluated for resistance to important biotic stresses in the region. Selected germplasm is both introgressed in the base populations and used to generate resistant source populations, inbred lines, and synthetics.