A B S T R A C TTo achieve an accurate phenotyping for drought tolerance, it is important to control water stress levels and timing. This study aimed to determine water use by upland rice plants during periods of irrigation withholding and its relationship with grain yield in order to increase the efficiency of this phenotyping. Two experiments were carried out in a randomized block design in which six water treatments (irrigation withholding for periods of 2, 4, 6, 8, 10 and 12 days) were compared, with four replicates. In the first experiment, treatments were applied at the R3 stage (panicle exsertion) and, in the second, at the R5 stage (beginning of grain filling). The amount of water evapotranspired was determined by the difference between the soil water storage at the beginning and at the end of irrigation withholding periods, from the surface to 80-cm depth. Evapotranspiration of upland rice from R3 stage was higher compared to that observed from R5 stage, when subjected to similar irrigation withholding periods in both growth stages. Rice grain yield is more sensitive to irrigation withholding imposed from R5 stage than from R3 stage.Evapotranspiração e produtividade do arroz de terras altas afetadas pela deficiência hídrica R E S U M O Para se obter fenotipagem acurada para tolerância à deficiência hídrica, é importante controlar o nível de estresse hídrico e a época de sua aplicação. Este trabalho objetivou determinar o uso de água pelas plantas de arroz de terras altas durante períodos de supressão da irrigação e sua relação com a produtividade de grãos, para aumentar a eficácia desta fenotipagem. Foram conduzidos dois experimentos no delineamento de blocos ao acaso e comparados seis tratamentos hídricos (supressão da irrigação por períodos de 2, 4, 6, 8, 10 e 12 dias) com quatro repetições. No primeiro experimento os tratamentos foram aplicados no estádio R3 (emissão das panículas) e no segundo, no estádio R5 (início do enchimento de grãos). A água evapotranspirada foi determinada pela diferença entre o armazenamento de água no solo no início e no fim dos períodos de supressão da irrigação, da superfície até 80 cm de profundidade. A evapotranspiração do arroz no estádio R3 foi mais alta comparada com a observada no estádio R5, quando submetida a período similar de supressão da irrigação em ambos os estádios. A produtividade do arroz foi mais sensível à supressão da irrigação imposta a partir do estádio R5 do que do estádio R3.

Water deficit is one of the environmental factors that cause a great reduction in the upland rice grain yield. The objective of this study was to evaluate genotypes of upland rice with broad genetic diversity for tolerance to this stress and to identify secondary traits for evaluation of this tolerance. Sixty-four genotypes were evaluated during two years at the Experiment Station of EMATER, in Porangatu, GO, under wellwatered and water deficit conditions. The genotypes showed differences in grain yield and were influenced differently by the water treatments, both under a mild water deficit in the first year and under a severe one in the second year. The genotype grain yield under water deficiency was significantly and positively correlated with tiller fertility, number of panicles m -2 , 100-grain weight, and plant height, and negatively with spikelet sterility and the number of days for the occurrence of 50% panicle emergence. It was also observed that the most productive genotypes under water deficit conditions showed lower leaf temperature, indicating improved water status. Nine genotypes were productive in both water conditions and three were productive only when well-watered.