Botryosphaeria diseases of proteaceae

[摘要] ENGLISH ABSTRACT:Fungi belonging to the genus Botryosphaeria are heterotrophic micromycetes that can bepathogens on woody plants. They cause serious, and in some cases devastating losses tocrops through leaf necrosis, stem cankers and plant death. The Proteaceae cut-flowerindustry in South Africa accounts for 70% of the national cut-flower enterprise.Botryosphaeria diseases are a major impediment to production and trade of Proteaceaeand there is an urgent need to investigate the etiology, epidemiology and control of thesediseases. Losses of one of the most important proteas, P. magnifica, amount to 50% ormore, locally. The main aims of this study were therefore to establish the etiology andaspects of epidemiology of Botryosphaeria stem cankers on P. magnifica and otherProteaceae, and to investigate methods of disease control.Although there is a vast body of information pertaining to this fungus, which wasreviewed in Chapter 1, there is relatively little information available on Botryosphaeriaon Proteaceae. The taxonomy of Botryosphaeria requires thorough review, andmolecular techniques need to be employed to resolve species identities.In Chapter 2, it was found that Phyllachora proteae, a leaf pathogen of proteas,produced a Fusicoccum anamorph, which is described as F. proteae. A sphaeropsis-likesynanamorph was associated with F. proteae and a new combination for P. proteae isproposed in Botryosphaeria, as B. proteae.The taxonomy of Botryosphaeria is in disarray at both the generic and the specificlevel. In Chapter 3 the taxonomic history of Botryosphaeria is reviewed, and the genuscircumscribed and distinguished from other morphologically similar genera. Althoughseveral anamorph genera have been linked to Botryosphaeria, based on morphologicalobservations and phylogenetic analysis of lTS rDNA sequence data, two anamorphgenera are now recognised, those with pigmented conidia (Diplodia), and those withhyaline conidia (Fusicoccum). Botryosphaeria proteae should thus be excluded fromBotryosphaeria.Several pathogenic Botryosphaeria spp. have an endophytic phase within theirhosts. They are therefore imported unwittingly into other countries where they may posea risk to agriculture and indigenous vegetation. The current global distribution ofBotryosphaeria spp. associated with Proteaceae is clarified and a key to these taxaassociated with Proteaceae is provided in Chapter 4. Five Botryosphaeria spp. areassociated with cut-flower Proteaceae worldwide viz. B. lute a, B. obtusa, B. protearum,B. proteae and B. rib is. B. protearum is described as a new species.A thorough understanding of disease epidemiology is essential to effect areduction of losses. In Chapter 5, I show that on P. magnifica, lesions caused byBotryosphaeria protearum, which lead to the formation of stem cankers, are initiated inthe mid-rib vein or margin of leaves. Koch's postulates were satisfied and it was foundthat the number of lesions that developed from artificial inoculations correlated withstarch levels present in leaves at the time of inoculation.In Chapter 6 it is shown that B. protearum exists as an endophyte in leaves of P.magnifica in naturally occurring as well as cultivated plants. In natural stands of proteasstem cankers are rare, but in cultivated plantations the incidence is high. Nutritionalanalyses indicate that higher levels of nitrogen occur in leaves of cultivated plants inspring, which could enhance disease development. High levels of sodium in the leaves ofwild plants may restrict disease development.The severe economic losses caused by B. protearum make the search forimproved methods of disease control essential. Fungicide applications form an importantcomponent of an integrated approach to disease management. In Chapter 7, in vitro testsdemonstrate that tebuconazole, benomyl, prochloraz me, iprodione and fenarimol reducethe mycelial growth of B. protearum effectively. In the field there was a 25-85%reduction in the occurrence of stem cankers by applying fungicides or sanitation pruning.The best control was achieved by using benomyl, bitertanol, fenarimol, iprodione,prochloraz manganese chloride alternated with mancozeb and tebuconazoleprophylactically. If sanitation pruning is combined with regular applications offungicides, disease can be combated.

[发布机构] Stellenbosch University