Diversity of fungi colonizing leaves of Rhododendron (Rhododendron L.) cuttings

Rhododendrons (Rhododendron L.) are shrubs whose attractiveness is determined by their multi-coloured flowers and evergreen leaves. Necroses visible on the leaves of rhododendron cuttings diminish the suitability of nursery material for marketing. These symptoms are most frequently caused by fungi. The investigations were conducted in 2010–2011 in an ornamental shrub nursery to identify fungi colonizing the phyllosphere of rhododendron cuttings and causing leaf necroses. The material for analysis consisted of leaves of 11 rhododendron cultivars. 550 leaves were collected from 110 half-year-old cuttings for mycological analysis. Over 350 fungal colonies belonging to 15 species were isolated from the leaves of rhododendron cuttings. The dominants included: Pestalotiopsis sydowiana, Trichoderma koningii and Alternaria alternata. The influents included: Aspergillus brasiliensis, Mucor hiemalis f. hiemalis, Epicoccum nigrum, Sordaria fimicola and Umbelopsis isabellina. A large majority of the fungi preferred the phyllosphere environment of Yakushima rhododendron (R. yakushimanum) cultivars ‘Sneezy’ and ‘Golden Torch’ as well as of the large-flowered cultivars ‘Flautando’, ‘Dominik’, and ‘Simona’. The phyllosphere of the large-flowered cultivars ‘Bernstein’, ‘Nova Zembla’, and ‘Goldbuckett’ was a reservoir for many fungal colonies and fungi species. The cultivars less susceptible to colonization by fungi and the most promising for planting in green areas and home gardens are the large-flowered cultivars ‘Bernstein’, ‘Nova Zembla’, ‘Goldbuckett’, ‘Rasputin’, and ‘Roseum Elegans’