Botryosphaeriaceae on native and exotic Myrtaceae trees in southern and eastern Africa

Abstract

Preface Members of the Botryosphaeriaceae represent a diverse family of fungi with over 180 species. They have been reported from a wide range of hosts occurring as endophytes, saprophytes or pathogens. These fungi are commonly referred to as latent opportunistic pathogens as they cause disease when the host is under abiotic or biotic stress. Symptoms associated with infection include tip die-back, stem and branch cankers, fruit rots, leaf spots and in severe cases mortality of trees. However, they are best known as canker and die-back pathogens on woody plants including species such as Eucalyptus (Myrtaceae). This dissertation focusses on the Botryosphaeriaceae on native and introduced Myrtaceae in southern and eastern Africa and aimed to increase current scientific knowledge of these fungi in the region. The literature review of this dissertation provides background to the research chapter by discussing the historic taxonomic changes in the Botryosphaeriaceae, and the current methods used for identification and classification of the species in this family. Furthermore, it summarizes the knowledge pertaining to Botryosphaeriaceae species on Eucalyptus and native Myrtaceae trees, particularly in eastern and southern Africa. Importantly, it considers fungal host jumps/shifts and their future impact in relation to Eucalyptus plantation forestry in Africa. Consideration is also given to the biology, ecology and possible future impacts of the Botryosphaeriaceae. Eucalyptus is the largest genus in the family Myrtaceae. Most species in this genus originates from Australia and were introduced to other countries as non-natives. In most parts of the world, Eucalyptus plantations are established in close proximity to native trees making it possible for pathogens to move from the native to the non-native trees and vice versa. This movement could result in considerable damage to the Eucalyptus plantations and the native trees. Chapter two of this dissertation focuses on identifying the Botryosphaeriaceae species occurring on both native and the non-native Myrtaceae trees in the Limpopo Province of South Africa and selected countries in southern and eastern Africa. Furthermore, it aimed at understanding the implications of the host jumps/shifts between the native and the non-native trees and their importance in relation to plantation forestry in eastern and southern Africa. This was achieved by sampling trees from South Africa, Malawi, Mozambique, Tanzania and Zimbabwe. Species resembling Botryosphaeriaceae were identified to species level using multi-gene DNA sequence data. To study the implications of the host jumps/shifts on Eucalyptus plantations, isolates obtained from native Myrtaceae trees were tested for pathogenicity under glasshouse conditions. The work presented in this dissertation provides a foundation of knowledge regarding the occurance and distribution of Botryosphaeriaceae species on several native Myrtaceae and Eucalyptus trees in eastern and southern Africa. This information is especially important in light of the fact that the areas from which isolates were obtained had not been considered previously. Furthermore, it suggests future directions to better understand the biology and taxonomy, movement, role and influence of Botryosphaeriaceae species on both native and non-native Myrtaceae trees.