Light Microscopic Study of the Lichens Xanthoria Parietina and Diploicia Canescens Infecting Citrus Trees in Egypt

Abstract

The lichens Xanthoria parietina and Diploicia canescens are the most abundant lichens infecting citrus trees at Sharkia Governorate. The freezing microtome was used to study the anatomy characters of both lichens as well as the physical contact between their thallus and the tissues of citrus tree’s bark and twigs. The thallus structure of Xanthoria parietina exhibited the common organization of foliose lichens, consisting of an upper cortex, algal layer, medulla, lower cortex, and rhizines. No penetration was noticed except the loosely cork layer in the center point of contact.

Conclusion: The anatomy of the lichen D. canescens thallus showed a typical crustose  lichen layers, i.e., upper cortex, algal layer, and medulla. The thallus was in direct contact with bark tissues due to the absence of lower cortex and rhizines. Superficial penetration, by the lichen hyphae through the cork tissues, was noticed, which caused disruption and separation of the cork layer.