First report of Phytophthora citrophthora causing leaf necrosis and terminal shoot dieback on Asimina triloba (pawpaw) in a Virginia floodplain forest

Abstract

Asimina triloba (pawpaw) is a shade-tolerant, understory, deciduous tree in the family Annonaceae that is native to 26 states in the eastern U.S. with a range from the Florida panhandle to New York, west to Iowa and Nebraska, and south to Texas. On 12 June 2022, in a floodplain forest along the James River near Richmond, Virginia, a group of three A. triloba saplings about 1.0 to 1.5 m tall were observed with leaf necrosis, terminal shoot dieback, and leaf drop. Symptomatic tissue was cultured on selective media and isolate DB22-4 was identified as Phytophthora citrophthora using morphological and molecular methods. A segment of the ITS and COX1 loci were deposited in the Genbank database under accession numbers OQ703042 and OQ834750, respectively. Koch’s postulates were fulfilled in a non-wounded, attached-leaf assay by inoculating 20 leaves on five healthy saplings. To the authors knowledge, this is the first report of P. citrophthora causing terminal necrosis and leaf drop on A. triloba in a nursery or a natural ecosystem. Additional studies are needed to understand the environmental and physiological factors that favor infection of A. triloba by P. citrophthora in the forest under natural conditions.