Abstract:Drought stress during wheat (Triticum aestivum L.) grain filling can affect the grain yield and its quality; effects that in some regions can be increased by the event La Niña, the cold phase of the climatic phenomenon El Niño Southern Oscillation. The aim was to evaluate if the evolution of relative water content (RWC) and stomatal conductance (gs) can be related to grain yield and its quality. Four spring wheat cultivars grown in the southern cone of South America were subjected to two levels of irrigation applied after anthesis, a wellwatered treatment (Control), and another with 50 % of the Control (Stress). RWC and gs were determined weekly during the stress period and agronomic traits at harvest. With a mean grain yield decrease of 14.8 % (P