Botryosphaeriaceae species associated with branch dieback and decline of macadamia trees in South Africa

Botryosphaeriaceae species are important latent pathogens causing diseases on trees utilized in forestry and agriculture. In recent years, there has been an increase in the incidence and severity of branch dieback and decline on macadamia trees in South Africa, and species of Botryosphaeriaceae have been considered as a possible cause. Although botryosphaeria dieback has been well-studied in Australia, there is little information regarding these fungi on Macadamia in South Africa. The aims of this study were consequently to (i) identify species of Botryosphaeriaceae from Macadamia branches from main production regions in South Africa, (ii) compare the diversity of species between symptomatic and asymptomatic branches, as well as between different growing regions, (iii) and to consider their relative importance in causing dieback. Eight species and three putative hybrids of the Botryosphaeriaceae were identified based on a phylogenetic comparison of sequence data from the ITS rDNA, tub2, tef-1 alpha and rpb2 loci. These included an unidentified Diplodia sp., and Lasiodiplodia sp., as well as L. gilanensis, L. theobromae, L. pseudotheobromae, Neofusicoccum kwambonambiense, N. luteum, N. parvum and three hybrid species. The unidentified species of Diplodia., Lasiodiplodia sp., L. gilanensis, and N. kwambonambiense are reported for the first time on Macadamia in South Africa. All species showed a potential to cause branch dieback symptoms, with species of Neofusicoccum identified as the most aggressive species. This study revealed a high level of diversity of Botryosphaeriaceae species and illustrates their potential as causal agents of dieback on Macadamia in South Africa.