First Report of Phytophthora nicotianae Causing Leaf Necrosis on Magnolia ‘Butterflies’ in a Virginia Ornamental Plant Nursery

Abstract

Magnolia ‘Butterflies’ is a hybrid cultivar resulting from a cross between M. acuminata and M. denudata. On July 6, 2021, during a survey at a Fairfax County, VA ornamental plant nursery, 6 out of 11 plants in 18.9-liter pots exhibited leaf necrosis and premature senescence on the lower branches. Phytophthora nicotianae was identified as the causal agent by morphology and sequencing. A segment of the internal transcribed spacer (ITS) and the cytochrome c oxidase subunit 1 (COX1) was deposited in Genbank under accession numbers ON586858 and ON605612, respectively. Koch’s postulates were fulfilled by an attached leaf, living plant inoculation trial. To our knowledge, this is the first report of this species causing foliar necrosis on Magnolia ‘Butterflies’ in a nursery or in the field. Further pathogenicity tests are needed to understand whether hybrids of Magnolia differ in susceptibility to infection when compared with their progenitors.