Eucalyptus scab and shoot malformation : a new disease in South Africa caused by a novel species, Elsinoe masingae

Abstract

A serious new disease of Eucalyptus was detected in South African plantations of these trees during the summer of 2021/2022. The first symptoms are minute dark spots on young leaves, petioles and shoots, becoming scab-like as the spots age. On highly susceptible Eucalyptus genotypes, leaves and shoots can become malformed leading to a ‘feathering’ appearance in the tree canopies and in the case of heavy infections, leaf and shoot death occur. Isolations made directly from developing scabs resulted in slow-growing cultures. These were identified, based on phylogenetic analyses of DNA sequence data for the ITS, LSU, TEF1 and RPB2 regions, as a novel species of Elsinoe (Elsinoaceae, Myriangiales), described here as E. masingae. Inoculations of an Eucalyptus grandis × Eucalyptus nitens hybrid variety produced the same symptoms as those observed under natural conditions and the pathogen could be re-isolated from the emerging lesions. Elsinoe masingae is closely related to, but clearly distinct from, the recently described Elsinoe necatrix that causes a serious scab and shoot malformation disease on Eucalyptus in Indonesia. Field surveys revealed significant variation in the susceptibility of different Eucalyptus genotypes, with the most severely affected genotypes including an E. grandis × nitens and an E. grandis × urophylla hybrid variety and E. grandis. The disease has also been observed on Eucalyptus amplifolia and on Eucalyptus dunnii, which had mild infections. The observed variation in susceptibility of Eucalyptus planting stock should provide opportunities to avoid serious damage because of scab caused by E. masingae in the future.