Desempenho agronômico de híbridos de milho submetidos a diferentes desfolhas

Abstract

Maize (Zea mays L.) cultivation has greatly evolved in several aspects in the past decades. These sets of changes, together with the need for more conclusive and available information about interactions that occur in the plant, are fundamental for the understanding of plant behavior when subjected to environmental challenges. Studies on the effects of maize defoliation, mainly during grain filling, are needed. The objective of this study was to evaluate the effects of maize defoliation on yield and on other agronomic traits. The trials were conducted in Fazenda Pombo, Uberlândia, MG, located at 860 m above sea level, in an area of grain production under no tillage. A randomized block design with 6 replications was used, as an 8 x 3 factorial, with 8 levels of defoliation and 3 hybrids. For defoliation evaluation, T1 was the control, where no leaves were removed, and T2 was the detasseled treatment. The remaining treatments consisted of leaf removal at the R2 stage (grain filling), where: T3 removal of two top leaves; T4 removal of four top leaves; T5 removal of all leaves above the main ear; T6 removal of four intermediate leaves, one above the main ear, the ear leaf and the two below it; T7 removal of all leaves below the main ear and T8 complete defoliation. The hybrids were NB 7253 (single cross HS), NB 6415 (double cross HD) and NB 7376 (triple cross HT). The traits evaluated were yield; density of ear, cob and stalk; 1,000 kernel weight; rotten grains; number of kernels per ear; number of kernels per ear row and number of ear rows; resistance to uprooting and stalk lodging resistance. It was observed that the loss of leaves in R2 stage had a negative impact on all evaluated traits, and that leaf losses greater than 40% significantly jeopardized yield and other production traits, such as number of kernels per ear, number of kernels per ear row and number of ear rows. Moreover, 1000 kernel weight, ear density and stalk and root quality, were affected regardless of defoliation intensity. The top leaves were the main responsible for grain filling. Complete defoliation considerably increased plant susceptibility to lodging and rotten grains. The removal of all leaves above the main ear was the most harmful treatment, leading to 14% yield loss.