Cotton cultivation in Brazil tends to occur mostly in the rainy season, and at the time of developing the crop there are often prolonged periods of low solar radiation. The objective of this work was to evaluate the root development of cotton cultivars subjected to shading in the initial phase. The experiment was carried out in a greenhouse, using rhizotrons. The experimental design was a 2x2 factorial in randomized blocks with five replications. The treatments were composed of cotton cultivars TMG 1WS (early) and TMG 8WS (late) and luminosity conditions: non-shaded and shaded (50% reduction of luminosity). There were no interactions between the factors “shading” and “cultivars” for any parameter evaluated. Shading reduced total and lateral root growth from the 21 days after emergence (DAE) and the main root at 24DAE. Shading caused reductions in length (60%), surface (65%), mean diameter (15%), root volume (69%), root dry matter mass (83%) and shoot (64%), as well as decreasing the content (36%) and the accumulation of carbohydrates in the shoot (73%). Shading at early cotton development reduces the shoot carbohydrates production, affecting dry matter accumulation and root growth, and this response is independent of the cultivar.

RESUMOO tamanho da muda de pimenta dedo de moça no momento do transplante para o campo pode determinar sua viabilidade e posterior produtividade. O Objetivo do trabalho foi avaliar o tamanho das mudas de pimenta dedo de moça com relação a diferentes frequências de irrigação. As plântulas foram submetidas a 4 diferentes frequências de irrigação. Os parâmetros biométricos das mudas foram avaliados aos 21 DAS. As mudas submetidas à irrigação na freqüência de 2 vezes ao dia apresentaram tamanho até 6% superior aos demais tratamentos. Palavras chaves: eficiência do uso da água; manejo de irrigação; pimenteira.