Chrysoporthe canker is one of the most important diseases of plantation-grown Eucalyptus spp. in tropical and subtropical regions worldwide. For many years, the disease was reported to be caused by the fungal pathogen Cryphonectria cubensis. Recent DNA-based studies have shown that the fungus in South Africa is not conspecific with Chr. cubensis and it was recently described in the new genus Chrysoporthe as Chrysoporthe austroafricana. Chr. austroafricana is known only from South Africa, where it causes severe cankers on Eucalyptus spp. and on ornamental Tibouchina trees, both of which have been introduced into South Africa. The origin of Chr. austroafricana is unknown, but it is possible that it expanded its host range from native trees related to Eucalyptus and Tibouchina spp. to these exotic hosts. Subsequent surveys of some indigenous South African Myrtales led to the discovery of fruiting structures resembling those of Chr. austroafricana on native Syzygium cordatum and S. guineense. The fungus from these Syzygium spp. was identified as Chr. austroafricana based on morphological characteristics and β-tubulin gene sequences. Pathogenicity trials showed that Chr. austroafricana is more virulent on exotic Eucalyptus spp. than on native S. cordatum. This study represents the first report of Chr. austroafricana from native hosts in South Africa and adds credence to the view that the fungus could be native to this country.

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Summary Ceratocystis albifundus causes the disease known as wattle wilt of non‐native Acacia mearnsii trees in South Africa, Uganda and Kenya. Infection results in rapid wilt and death of susceptible trees and stem cankers on more tolerant trees. It has been suggested that C. albifundus is indigenous to southern Africa, possibly having spread from native Protea spp. to non‐native A. mearnsii and A. decurrens trees. Although C. albifundus has been collected from Protea spp., these reports are based on limited records for which only aged herbarium specimens exist. During surveys of wound‐infecting fungi on native tree species in South Africa, a fungus resembling C. albifundus was collected from Protea gaguedi, Acacia caffra, Burkea africana, Combretum molle, C. zeyheri, Faurea saligna, Ochna pulchra, Ozoroa paniculosa and Terminalia sericea. The identity of the fungus was confirmed as C. albifundus, using comparisons of DNA sequence data for the ITS and 5.8S gene of the rRNA operon. In pathogenicity trials, lesions were produced on C. molle and A. caffra, with some trees beginning to die at the termination of the experiment. This study represents the first report of C. albifundus from native tree species in South Africa and provides unequivocal evidence that the fungus occurs naturally on native Protea spp. The wide host range of C. albifundus, as well as its abundance on these indigenous hosts lends further support to the view that it is a native African pathogen.

Species of Ceratocystis Ellis and Halstead s.l. include important plant pathogens such as C. albifundus Morris, De Beer, and M. J. Wingfield that causes a serious wilt disease of non-native, plantation-grown Acacia mearnsii De Wild. trees in Africa. The aim of this study was to identify the insects associated with C. albifundus in South Africa and to consider the means by which the pathogen spreads. Insects were collected weekly for 77 wk in a native ecosystem using modified pitfall traps. Trapped insects were identified, and fungi were isolated using carrot baiting and by plating them onto malt extract agar. Fungi were identified using morphological characteristics and DNA sequence comparisons. Three different nitidulid (Coleoptera: Nitidulidae) beetles, Brachypeplus depressus Erichson, Carpophilus bisignatus Boheman, and Ca. hemipterus L, were collected, of which the most common were the Carpophilus spp. Two Ceratocystis spp., namely C. albifundus and C. oblonga R. N. Heath and Jolanda Roux, were isolated from all three insect species. Insect numbers and fungal isolates decreased significantly in the colder months of the year. Of the two Ceratocystis spp., C. oblonga was most abundant, occurring on 0.5% of the Carpophilus spp. C. albifundus was isolated from 1.1% of the Brachypeplus individuals and from 0.01% of the Carpophilus individuals. This study presents the first record of insects associated with C. albifundus and C. oblonga and provides an indication of environmental influences on fungal and insect populations, which could contribute to future disease management.

Ceratocystis fimbriata sensu lato (s.l.) is an important pathogen of Eucalyptus. Pathogenicity of isolates has typically been evaluated by inoculating seedlings under greenhouse conditions. It is, however, not clear how accurately this reflects pathogenicity under field conditions. In this study, five techniques to potentially screen C. fimbriata isolates for their relative pathogenicity to Eucalyptus were compared. These included: in vitro growth comparisons on artificial media; inoculations on apples; inoculation on Eucalyptus seedlings in a greenhouse; inoculations on Eucalyptus bolts freshly cut from stems of young trees; and field inoculations on young trees. Eight isolates of C. fimbriata s.l. collected from various areas in South Africa were used. There was considerable variation in growth in culture and aggressiveness of the eight isolates. Field inoculations on young trees were best correlated with inoculations of bolts (r = 0.76). Lower correlation coefficients were obtained with seedlings (r = 0.59), apple inoculations (r = 0.56), and in vitro colony growth (r = 0.42). Inoculation of bolts provides a rapid and reliable method to screen isolates of C. fimbriata s.l. for pathogenicity to Eucalyptus.