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Early detection of diseases in urban sentinel plantings: A case study with Botryosphaeriaceae associated with the die-back of Sequoiadendron giganteum in Croatia

Giant sequoia (Sequoiadendron giganteum) is a large, long-lived, evergreen coniferous tree endemic to the western slopes of the Sierra Nevada Mountains in California, Western North America. Sequoiadendron giganteum is in danger of extinction due to its population decline and fire risks and it has been listed in the IUCN red list of threatened plants. In Croatia, S. giganteum is planted as a specimen and shade tree in parks, botanical gardens, and arboreta. In recent years, S. giganteum trees have exhibited die-back of stems and branches accompanied by resin flow, needle necrosis and reddish-brown discoloration of sapwood. The disease symptoms were typical of opportunistic pathogens residing in the fungal family of the Botryosphaeriaceae (Ascomycota: Botryosphaeriales). Diseased and apparently healthy S. giganteum trees were sampled in March 2017, in the Botanical garden, in Zagreb, Croatia. Samples of symptomatic and asymptomatic tissue were plated on Malt Extract Agar acidified with lactic acid (AMEA). The constantly isolated fungal colonies were fast-growing, grey and Botryosphaeriaceae- like and the aim of this study was to identify them. Based on morphological characteristics of the asexual morph and phylogeny for the internal transcribed spacer (ITS), translation elongation factor 1α (TEF 1-α) and β-tubulin-2 (BT2) gene regions isolates were identified as Botryosphaeria dothidea and Neofusicoccum parvum. This study complements knowledge on the diversity and distribution of the Botryosphaeriaceae and illustrates the value of urban sentinel plantings for the early detection of potential diseases. The risk of spread or damage of these fungal species should be assessed in order to develop risk mitigation measures where appropriate.

Botryosphaeriales, dieback disease, morphology, urban tree pathogens, urban sentinel plantings

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