Histological disturbances caused by Microcyclus ulei and Colletotrichum spp. in rubber trees (Hevea brasiliensis)

ABSTRACT

The two main diseases affecting the rubber tree in Colombia are South American leaf blight caused by Microcyclus ulei and anthracnose caused by Colletotrichum spp. These pathogens affect the leaf tissue and, under favorable climate conditions, can lead to total defoliation of trees. Healthy and symptomatic leaves in different phenological stages of the GT1 clone were histologically sectioned and double stained with safranin-fast green, before pictures were obtained under a light microscope. Tissue organization was observed in healthy leaves, evidencing that mature leaves had a thin wax layer, which was absent in young leaves. Early stages of leaves infected by M. ulei showed degradation and disorganization of the epidermis, parenchyma (palisade and spongy) and vascular bundles, while mature leaves had formation of stromata together with epidermis loss, elongation and lignification of the palisade parenchyma cells, besides partial lignification. Young leaves infected by Colletotrichum spp. showed depressions in the epidermis, accompanied by the presence of lignin; mature leaves presented pronounced depressions with strong lignification and degradation of the spongy or palisade parenchyma and sometimes both processes occurred. Fungal hyphae and conidia were observed in some mesophyll cells. In conclusion, infection by both pathogens causes histological damage of varied degrees according to the age of the tissue and the visual symptoms.

Keywords
rubber tree; histopathology; foliar diseases; ontogenic resistance