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FABI Articles : Unexplored Ophiostomatoid Fungal Diversity in South Africa

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Species in the genera Ceratocystis Ellis & Halsted (Microascales) and Ophiostoma H. & P. Sydow (Ophiostomatales) and their asexual forms are collectively referred to as the ophiostomatoid fungi. This name arises from their morphological similarities and convergent evolution of morphological structures adapted to insect dispersal (Wingfield et al., 1993). These two genera include important tree pathogens that typically infect wounds visited or made by their insect vectors. Well-documented examples of tree pathogens are O. ulmi (Buisman) Nannf. and O. novo-ulmi Brasier, responsible for the Dutch Elm disease pandemics in Europe and North America, C. fagacearum (Bretz) Hunt, a damaging wilt pathogen of Quercus spp. in the USA (Sinclair & Lyon, 2005) and species in the C. fimbriata sensu lato complex (Kile, 1993). There are also many saprotrophic species that cause blue-stain of lumber, reducing its commercial value (Seifert 1993).

 

Very little information is available regarding diseases of native trees in South Africa and until recently, only one pathogen, Ceratocystis albifundus, the cause of wattle wilt of non-native Acacia mearnsii trees, was known from these trees. The fungus was first reported (as C. fimbriata) from native Protea spp. in the 1970's (Gorter 1977), but was not known from diseases of native trees. In recent studies C. albifundus, has been found on seven native tree genera (Roux et al., 2007), supporting the view that the fungus is native to South Africa (Barnes et al., 2005, Roux et al., 2001). This provided motivation to determine whether other ophiostomatoid fungi occur on native trees in the country.

 

Surveys were conducted in three main areas of South Africa where native trees occur abundantly. These included the Kruger National Park (Mpumalanga Province), Leeuwfontein Collaborative Nature Reserve (Gauteng Province) and Groenkloof Forest (Tsitsikamma Forests, Western Cape Province). Wounds from which samples were collected included damage caused by elephants (FIG A), kudu, eland (FIG B), wind as well as those made artificially by local traditional healers when they collect bark and wood for medicinal purposes (FIG C). Fungi isolated from samples were identified using morphological studies and multigene sequence phylogeny.

 

Numerous Ceratocystis and Ophiostoma isolates were collected from eight native tree genera spanning six different families. These included Acacia nigrescens (Leguminosae), Combretum zeyheri Sond. (Combretaceae), Sclerocarya birrea (Anacardiaceae), Burkea africana Hook. (Leguminosae), Faurea saligna Harvey (Proteaceae), Ocotea bullata (Burch.) Baill. (Lauraceae), Rapanea melanophloeos (Myrsinaceae) and Terminalia sericea Burch. ex Dc. (Combretaceae).

 

Five fungal species were identified from the native trees in this study, three of which represent new species. The fungi included C. albifundus, O. quercus, and Pesotum fragrans. Previously unknown taxa were described as Ceratocystis tsitsikammensis (FIG D) (referring to the Tsitsikamma forests of South Africa), infecting Rapanea melanophloeos trees; Ceratocystis savannae (FIG E) (referring to the Savanna vegetation type where the fungus was found), infecting Acacia nigrescens and Combretum zeyheri trees; Ophiostoma longiconidiatum (FIG F) (referring to the unusually long conidia found in the anamorph state of this fungus). Of these fungi, only C. tsitsikammensis appears to be capable of causing disease, resulting in serious lesions on R. melanophloeoes trees in green-house inoculation trials.

 

Discoveries made in this study have clearly shown that, the diversity of ophiostomatoid fungi infecting native trees in South Africa is poorly known. Future studies similar to this one will most likely reveal many other species, some of which could have economic and ecologic importance.

 

UNEXPLORED OPHIOSTOMATOID - Image 1

 

Related Publication

Kamgan NG, Jacobs K, de Beer ZW, Wingfield MJ, Roux J. 2008. Ceratocystis and Ophiostoma species, including three new taxa, associated with wounds on native South African trees. Fungal Diversity 29: 37-59.

 

 


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