Anatomical responses in apricot wood structure caused by Valsaria insitiva

Understanding anatomical responses in various tree species to fungi causing gummosis is limited. In this article, wood samples from an apricot tree (Prunus armeniaca) with severe gummosis and branch dieback were studied macroscopically and microscopically to determine the response of woody tissues to the infection. The fungi species Valsaria insitiva was determined visually by the signs of the disease and by cultivating clean cultures. Macroscopical examination found wedge and arch shaped necroses running along the growth rings under the bark necroses and sunken lesions. Microscopical examination found small black fruiting bodies of the fungus on the bark. Vessels and libriform fibers were blocked by gum, thus blocking the water and nutrients flow to the branches and causing the dieback. Sites with fungi infection were compartmentalized and this was discussed according to the CODIT model. Oxidized ray parenchyma was visible in tangential and cross sections of the wood; calluses were covering the infected areas. Compartmentalizing the infections by releasing gum into vessel lumina, restricting the flow of nutrients and water in the tree thus drying it out is a way of protection of the tree against the pathogens. Apoplexy of apricots is an acute disease and can be very extreme in some cases. The studied tree had signs of compartmentalization of the infection, but the infection was spreading faster than new tissues were formed.