A major production constraint in acid upland soils is Al toxicity. So far, screening rices for Al tolerance has been limited to upland cultivars. However, lowland rice is grown on about 2 million ha with acid sulfate soil conditions. These rices are prone to Al toxicity during dry spells. Several Al-tolerant upland rices have been identified, but their use in acid lowlands as cultivars or as donors for breeding purposes is very limited because they are japonicas.