First report of honeysuckle leaf blight (Insolibasidium deformans) on honeysuckle (Lonicera spp.) in the UK

Honeysuckle belongs to a popular genus of ornamental shrubs (many of which are climbers), grown mainly for their fragrant flowers. Over the last few years, many species and varieties of honeysuckle have become affected by a pathogen newly introduced into the UK: the basidiomycete Insolibasidium deformans, which causes honeysuckle leaf blight. The disease was first observed in the UK in early summer 2000 on a containerised plant of Lonicera pileata. Since then, the disease has become more widespread in the UK on Lonicera spp., especially in the south of England. Symptoms are first seen in the spring as interveinal chlorotic lesions on newly emerged leaves. As these lesions develop, they become yellow/brown and turn silvery as they dry out (Fig. 1).

A curling or twisting of entire leaves is often seen and affected leaves often drop prematurely. Stems appear to remain symptomless. A white bloom consisting of basidia and basidiospores is evident on the undersurface of infected leaves (Fig. 2). Basidia observed on UK samples were four celled, cylindrical, curved (4-6 x 20-35 µm) with short cylindrical, slightly curved, hyaline, apiculate basidiospores (5-7 x 9-13 µm) that conformed to I. deformans (Oberwinkler & Bandoni, 1984). Pathogenicity was tested by dusting healthy plants of L. pileata and L. nitida with basidiospores from an infected plant. Uninoculated plants were used as controls. Typical interveinal chlorotic symptoms were observed after a few weeks on L. pileata, but not on L. nitida. No symptoms were found on the control plants.

Honeysuckle leaf blight has previously been recorded on Lonicera in at least fourteen north-eastern and north-central states of the USA and from Canada (Riffle et al. 1986). This is the first report of the disease in the UK and the pathogen is now considered to be established here.