Fungal and bacterial diseases on ornamental trees, shrubs, hedges and climbing plants detected in the last 20 years in northern Italy

The increasing request of new species and varieties characterizing the sector of ornamental plants determines the introduction of new pathogens and the rapid evolution of phytopathological problems. This review examines the diseases caused by fungi and bacteria on trees, shrubs, hedges and climbing plants detected in Piedmont (northern Italy) in the last 20 years. Among the trees, a powdery mildew caused by Oidium subgen. octagoidium was detected on Acer negundo, whereas Erysiphe pulchra was identified on Cornus florida. On the latter host, a grey mould caused by Botrytis cinerea was reported. A leaf spot caused by Colletotrichum kahawae appeared on Liquidambar styraciflua. Botryosphaeria parva caused a die-back on an ancient tree of Rhododendron sp., whereas Pycnostysanus azaleae produced the bud blast described on several rhododendron cultivars. Ciborinia camelliae was the causal agent of a flower blight observed on a collection of camellia varieties. A bacterial leaf spot caused by Pseudomonas syringae was detected on Crataegus laevigata 'Paul's Scarlet'. Among the shrubs, a powdery mildew caused by Erysiphe azaleae was observed on Rhododendron japonicum × R. molle. Root roots caused by Phytophthora nicotianae and P. cinnamomi were reported on Edgeworthia papyrifera and Kalmia latifolia respectively. Leaf spots caused by Alternaria alternata and Boeremia exigua var. exigua were detected on Hydrangea macrophylla and H. paniculata, respectively. Pseudomonas sargentii pv. viburnii causing a bacterial leaf spot, was isolated from Viburnum sargentii. Among the shrubs arranged in hedges and the climbing plants, Podosphaera spiraeae was the causal agent of powdery mildew on Spiraea japonica, whereas Oidium sp. subgen. pseudoidium was identified on Wisteria sinensis. Volutella blight caused by Pseudonectria buxi was detected on Buxus microphylla. Finally, some considerations about the appearance of these new diseases and about the control methods that can be used in Italy are presented.