Resumo Objetivou-se avaliar a adaptação de cultivares de alface com base na metodologia dos graus-dia, em estufa, no vale do Gurguéia. O experimento foi conduzido em ambiente protegido, na Universidade Federal do Piauí - UFPI/CPCE. O delineamento adotado foi em blocos ao acaso, sendo os tratamentos cultivares de alface. As cultivares utilizadas foram: Simpson, Bruna, Palmas e Grand Rapids - TBR. Os dados meteorológicos (temperatura do ar, umidade relativa, pressão atmosférica, velocidade dos ventos e precipitação) foram obtidos em uma estação meteorológica portátil que foi instalada no ambiente protegido. A temperatura do ar durante o experimento apresentou máxima de 33 °C e mínima de 26 °C. As cultivares ‘Simpson’ e ‘Grand Rapids’ apresentaram um ciclo mais precoce (45 dias), quando comparada às demais (52 dias), ambas com constante térmica (CT) de 898 °gd. As cultivares ‘Bruna’ e ‘Palmas’ apresentaram CT = 1050 °gd. Dentre as cultivares avaliadas, as cultivares ‘Palmas’ e ‘Bruna’ obtiveram comportamento e morfologia adequados em relação às altas temperaturas regionais. Dessa forma, conclui-se que as cultivares ‘Palmas’ e ‘Bruna’ possuem potencial produtivo para a região, quando cultivada em ambiente protegido.
Abstract The objective of this study was to evaluate the adaptation of lettuce cultivars based on day-degree greenhouse methods in the Gurguéia Valley. The experiment was carried out in a protected environment, at the Federal University of Piauí - UFPI / CPCE. The experimental design was a randomized block design, with treatments of lettuce cultivars. The cultivars used were: Simpson, Bruna, Palmas and Grand Rapids - TBR. The meteorological data (air temperature, relative humidity, atmospheric pressure, wind velocity and precipitation) were obtained in a portable weather station that was installed in the protected environment. The temperature of the air during the experiment presented maximum of 33 °C and minimum of 26 °C. The cultivars ‘Simpson’ and ‘Grand Rapids’ presented an earlier cycle (45 days), when compared to the others (52 days), both with a thermal constant (CT) of 898 °gd. The cultivars ‘Bruna’ and ‘Palmas’ showed CT = 1050 °gd. Among the evaluated cultivars, the ‘Palmas’ and ‘Bruna’ cultivars obtained adequate behavior and morphology in relation to the high regional temperatures. Thus, it is concluded that the ‘Palmas’ and ‘Bruna’ cultivars have productive potential for the region when cultivated in a protected environment.