Resposta espectral de folhas de Eucalyptus globulus (Labill.) atacadas por Mycosphaerella spp.

Abstract

Eucalyptus globulus one of the most important species for paper and pulp industries, nowadays faces development problems in several countries due to its susceptibility to the fungus Mycosphaerella spp., which causes leaf spots that may cause the crown defoliation. The study aims at analyzing the spectral behavior of E. globulus leafs in response to the severity of the disease caused by the fungus Mycosphaerella spp. The stand evaluated is located at Herval - RS. Four collections were performed during the different climate seasons. In each collection, with the aid of a spectroradiometer, we carried out the reading of the foliar reflectance with different severity levels (healthy, little affected, median attack and severely attacked) in leafs from the lower, medium and higher part of the crown. The reflectance values were then analyzed according to two divisions of the electromagnetic spectrum (visible and proximal infrared). The results obtained through ANOVA for the mean value of foliar reflectance in the visible band of the electromagnetic spectrum indicate the existence of differences between levels of severity, between the positions of collection, as well as interaction between two factors: position in the tree collection and disease severity. In the part of the electromagnetic spectrum that corresponds to proximal infrared, we verified significant differences between climate seasons, collection positions and severity level. It was found interaction between collection positions and climate seasons as well as among the three factors, climate seasons, and collection positions in the tree and disease severity. It was then possible to conclude that there are variations in the spectral behavior of severity levels according to leaf position in the tree and to the climate season. The reflectance of severely attacked leafs is clearly distinguished from leafs in the healthy and little affected levels.