Root growth and carbohydrate partitioning in cotton subjected to shading in the initial phase

EnglishCotton 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. Key words: root length; dry weight; radiation portuguesO cultivo do algodoeiro no Brasil esta concentrado no periodo chuvoso, e no momento do estabelecimento da lavoura frequentemente ha periodos prolongados de baixa radiacao solar. O objetivo deste trabalho foi avaliar o desenvolvimento radicular de cultivares de algodoeiro submetidos ao sombreamento na fase inicial da cultura. O experimento foi realizado em ambiente controlado, em rizotrons. O delineamento experimental foi um fatorial 2x2 em blocos ao acaso com cinco repeticoes. Os tratamentos foram as cultivares de algodao TMG 11WS (precoce) e TMG 81WS (tardia) e as condicoes de sombra: sem sombra e com sombra (50% de reducao da luminosidade). Nao houve interacao entre os fatores “sombra” e “cultivares estudadas” para nenhum parâmetro avaliado. A sombra reduziu o crescimento radicular total e das raizes laterais a partir dos 21 dias de emergencia (DAE) e da raiz principal aos 24DAE. O sombreamento reduziu o comprimento (60%), a superficie (65%), o diâmetro medio (15%), o comprimento por volume (60%), o volume radicular (69%), a massa de materia de seca da raiz (83%) e da parte aerea (64%), o teor (36%) e o acumulo de carboidratos na parte aerea (73%). Em conclusao, o sombreamento na fase inicial de desenvolvimento do algodoeiro reduz a producao de carboidratos da parte aerea, afetando o acumulo de materia seca e o crescimento radicular, sendo que essa resposta independe da cultivar. Palavras-chave: comprimento da raiz; peso seco; radiacao