New host associations and a novel species for the gall-inducing acacia rust genus Ravenelia in South Africa

Trees in the genus Vachellia (previously Acacia) are commonly infected by the gall-inducing rusts Ravenelia macowaniana 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 Vachellia xanthophloea and it is described here as R. xanthophloeae.