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

Małgorzata Żołna,Barbara Kierpiec-Baran,Maria Kowalik

doi:10.5586/aa.2014.004

Abstract

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’.

Highlights

Evergreen rhododendron (Rhododendron L.) shrubs owe their attractiveness to flowers enchanting with their colours and smell, and to the leaves forming the canopy
The analyzed material consisted of 11 rhododendron cultivars: R. brachycarpum ‘Flautando’, R. calophytum ‘Dominik’, R. catawbiense ‘Nova Zembla’, ‘Rasputin’, ‘Roseum Elegans’, ‘Simona’, R. dichroantum ‘Bernstein’, R. forrestii ‘Baden Baden’, R. wardii ‘Goldbuckett’, R. yakushimanum ‘Golden Torch’ and ‘Sneezy’. 550 leaves showing necrosis were collected from 110 half-year-old cuttings and used for mycological analysis
The highest number of fungal colonies were identified on the leaves of R. yakushimanum ‘Sneezy’, a slightly lower number was isolated from the large-flowered cultivars R. brachycarpum ‘Flautando’, R. calophytum ‘Dominik’, and R. catawbiense ‘Simona’

Summary

Introduction

Evergreen rhododendron (Rhododendron L.) shrubs owe their attractiveness to flowers enchanting with their colours and smell, and to the leaves forming the canopy. Necroses greatly decreasing the suitability of nursery material for marketing have been diagnosed on leaves of rhododendron cuttings in production nurseries. Leaf spot and necroses resulting in dieback and leaf fall in long-standing shrubs were presented in the papers by Kowalik and Muras [1] as well as by Kowalik et al [2,3,4], whereas the agents of leaf infection (fungi and fungus-like organisms) were identified in the works of Kowalik [5,6] and Kowalik et al [7,8]. Determining the agents causing necroses on the leaves of rhododendron cuttings provides the possibility to select cultivars less susceptible to colonization by pathogens causing dieback and falling of leaves to be planted in green areas and home gardens.

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