Abstract
Trees in the genus Vachellia (previously Acacia) are commonly infected by the gall-inducing rusts Raveneliamacowaniana and R.evansii. Rust galls bearing aecial infections and relating uredinial and telial infections on the leaves of nine Vachellia species not previously recorded to be infected by Ravenelia spp. have recently been collected in South Africa. The rust fungi causing these infections were characterised using molecular phylogenetic analyses of DNA sequence data of the LSU and ITS rDNA regions as well as morphological examinations. The host range of R.macowaniana and R.evansii was thus re-assessed and extended from four to nine species and from one to three species, respectively. Application of Principal Component Analyses (PCA) of telial morphological characters provided evidence of an effect of the host species on the teliospore morphology in R.evansii, but only minor effects in R.macowaniana. A novel gall-inducing Ravenelia sp. closely related to R.macowaniana, was found on Vachelliaxanthophloea and it is described here as R.xanthophloeae.
Highlights
Infected V. borleae, V. davyi, V. exuvialis, V. hebeclada, V. natalitia, V. permixta, V. swazica and V. xanthophloea trees were sampled during several field surveys in South Africa between 2004 and 2015
Maximum likelihood analysis of the combined dataset resulted in a phylogenetic tree that consisted of three highly supported groups representing R. evansii, R. macowaniana and a novel Ravenelia species described below (Fig. 1A)
In South Africa, this tree species is naturally confined to habitats with shallow watertables in low-altitude areas of the northeastern KwaZulu-Natal, Mpumalanga and Limpopo Provinces (Coates Palgrave 2005, Smit 2008)
Summary
Acacias can be found in all South African biomes. They play important ecological roles by providing food for insects, birds and game, as well as improving soil fertility through nitrogen fixation by their associated rhizobia (Ross 1979, Coe and Coe 1987, Coates Palgrave 2005, Smit 2008, Grellier et al 2012). In South Africa, acacias are commonly infected by rust fungi (Pucciniales) of the genus Ravenelia (Doidge 1950). Ravenelia includes more than 200 described species and is amongst the most species-rich genera of rust fungi (Cummins and Hiratsuka 2003). While the aecial stage of several macrocyclic species is known to cause hypertrophied tissues such as galls and witches brooms within host organs (Dietel 1894, Hernandez and Hennen 2003), the multicellular teliospores of Ravenelia are amongst the most complex spore forms found in the rusts
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