First report of Botryosphaeria dothidea causing shoot blight and cankers of pistachio in Australia

Shoot blight and cankers are reported for the first time from pistachio in Australia from 20-26 year old trees of a plantation in the Riverina, South West NSW. Shoot blight symptoms during late summer prior to harvest included dark lesions on current-season shoots, followed by blackening and dieback of the same structures. Cankers were observed in older wood, showing wedge-shaped discolouration in cross-sections of these branches. Microscopic investigation provided evidence of black pycnidia, indicative of Botryosphaeriaceae, on the surface of old cankerous wood. Isolations from surface sterilised symptomatic young shoots and old wood yielded in Botryosphaeriaceae cultures, which were identified via conidia morphology and ITS sequencing. All isolates were identified as the pistachio pathogen Botryosphaeria dothidea responsible for panicle and shoot blight as well as basal cankers of pistachio in other parts of the world. Pathogenicity from six of our isolates was confirmed with in vitro pathogenicity tests. Re-inoculation of actively growing cultures from our isolates into healthy young pistachio wood resulted in dark internal lesions varying between 5 and 40 mm length, while control inoculated wood showed no lesions or internal discolouration.