During the winter season of 1995 a field experiment was conducted in Piracicaba, SP, Brazil, to analyse the radiation use efficiency (<FONT FACE="Symbol">e</font>) and the harvest index (IC) of the wheat cultivar IAC-287 'YACO', when submitted to drought stress at different growth stages. The experiment was a randomized complete block design with five treatments and three replicates. The drought stress was applied during tillering, booting, grain filling and ripening stages. The radiation use efficiency for fitomass production (<FONT FACE="Symbol">e</font>F) was reduced by 22.8 and 15.4% when compared to the control treatment, for drought stress applied during tillering and booting stages, respectively. The drought stress, when applied during tillering, booting and grain filling stages, reduced the radiation use efficiency for grain production (<FONT FACE="Symbol">e</font>G) by 21.1, 22.2 and 22.2%, respectively, when compared to the control treatment. With regard to the harvest index (IC), the drought stress effect had a major impact on the grain filling stage, being reduced by 19.1% when compared to the control treatment. A less intense reduction of the harvest index, when compared to the control treatment, was also observed, when drought stress was applied during booting (7.5%, p < 0.05) and ripening stages (7.9%, p < 0.05).
wheat; drought stress; radiation; harvest index
