Defoliation of sweet corn plants under irrigation depths and its impact on gas exchange/Desfolha em plantas de milho doce sob diferentes laminas de irrigacao e seu impacto nas trocas gasosas

The objective of this work was to evaluate leaf gas exchanges of sweet corn as a function of defoliation when submitted to different irrigation depths. The experimental design was randomized blocks in split-plot scheme, with four irrigation depths in the plots [50, 75, 100 and 125% of crop evapotranspiration (ETc)], and three levels of defoliation in the subplots (0%, control; 35%, removal of four fully expanded leaves; 100%, total removal of the leaves--section of the aerial part) with three replicates. Defoliation was manually performed when the plant had four fully expanded leaves. It was verified that the dephs of irrigation and defoliation levels affect leaf gas exchanges in sweet corn plants, allowing the conclusion that the plant tends to activate a mechanism of photosynthetic compensation, when subjected to leaf stress, which can vary according to the degree of severity and water availability to which it is submitted. The most expressive values of gas exchanges in sweet corn plants that did not have defoliation were generally observed at irrigation depths estimated between 87 and 99% ETc and, in the treatments with defoliation, regardless of the level, at irrigation depth of 125% ETc. Key words: Zea mays L. var. saccharata water stress photosynthesis Objetivou-se neste trabalho avaliar as trocas gasosas foliares de plantas de milho doce em funcao da desfolha, quando submetidas a diferentes laminas de irrigacao. O delineamento experimental foi em blocos casualizados em esquema de parcelas subdivididas, tendo nas parcelas quatro laminas de irrigacao 50, 75, 100 e 125% da evapotranspiracao da cultura (ETc) e nas subparcelas tres niveis de desfolha (0%, testemunha; 35%, remocao de quatro folhas completamente expandidas; 100% remocao total das folhas--seccao da parte aerea) com tres repeticoes, sendo a desfolha realizada manualmente quando a planta apresentava quatro folhas completamente expandidas. Verificou-se que os niveis de irrigacao e desfolha afetam as trocas gasosas foliares em plantas de milho doce, permitindo a conclusao de que a planta quando submetida a estresses foliares, tende a ativar um mecanismo de compensacao fotossintetica, podendo variar em funcao do grau de severidade e da disponibilidade hidrica a qual esta submetida. Os valores mais expressivos de trocas gasosas em folhas de milho doce que nao tiveram desfolha foram, de forma geral, observados nas laminas de irrigacao estimadas entre 87 e 99% da ETc e nos tratamentos com desfolha,