Detection of Seiridium cardinale Causing Bark Cankers on Leyland Cypress (x Cupressocyparis leylandii) in Arizona

Leyland cypress (x Cupressocyparis leylandii) is an evergreen landscape tree that is fast-growing and widely used to create windbreaks or privacy screening in Arizona. In Jul 2021, branch dieback and tree mortality were observed in Leyland cypress trees. Other symptoms include changed needle color, yellowing, wilting, branch decline or longitudinal bark cankers on the stems and branches with resin exudates. Four branches with canker and resin exudates were collected for pathogen identification. Slow-growing fungal colonies on PDA had dense and floccose appearance with green or grayish-olive color in the center. Acervuli were formed on sterilized cypress twigs placed on water agar for 3 weeks under natural lighting provided by a nearby window with an eastern exposure (12-14 h photophase). Conidia were oblong-fusiform in shape with sizes ranging from 21-28 × 8-11 μm (15 measurements). Conidia were 5-septate with four dark brown media cells and two hyaline small end cells (1μm long). These morphological characteristics putatively classified the fungus as S. cardinale. ITS and BTUB DNA sequences confirmed its ID. To complete Koch's postulates, pathogenicity tests were conducted in the greenhouse on five 3-year-old Leyland cypress plants in 5-liter pots. This provides the first account of the occurrence of bark cankers caused by S. cardinale in Leyland cypress in Arizona.