Honeysuckle leaf blight reduces the growth of infected Amur honeysuckle (Lonicera maackii, Caprifoliaceae) seedlings in a greenhouse experiment1

Amur honeysuckle (Lonicera maackii) is an important invasive plant species in the Ohio River Valley. Previous work has shown extensive dieback of honeysuckle in the region, coupled with the appearance of the native fungal pathogen, honeysuckle leaf blight (Insolibasidium deformans). Our goal was to find if the blight causes growth decline or mortality in Amur honeysuckle. Seedlings were grown under greenhouse conditions in 2017. Treated seedlings were sprayed with a spore solution prepared from blighted leaves that were collected from the field. They were placed into a growth chamber with conditions set for optimum spore growth and then returned to the greenhouse after leaf blight began to develop. Growth (height, total stem length, leaf area, and leaf number) and dark-adapted chlorophyll fluorescence (Fv/Fm) were measured periodically over the growing season. A repeated-measures analysis of aboveground growth indicated that larger, faster-growing plants were more likely to be infected, but their growth rates were subsequently reduced much more than uninfected treated plants and controls. There were positive correlations between Fv/Fm and RGR (relative growth rate). Blighted leaves had lower values of Fv/Fm than uninfected leaves. No infected plants died, but this experiment supports our hypothesis that leaf blight causes a significant growth decline in Amur honeysuckle. Future work will determine if the patterns seen under greenhouse conditions hold in the field.