by
I.A.S. Gibson
Oxford, U.K
BACKGROUND
In September 1980, a canker disease caused by Cryphonectria cubensis (Bruner) Hodges was recorded in young Eucalyptus urophylla plantations at Mangombe, Edea, United Republic of Cameroon.
Diagnosis of this disease was made by the Commonwealth Mycological Institute, Kew, U.K., from specimen material collected by Dr. F.B. Armitage (IMI 249406) and has been confirmed from later collections.
This is the first record of C. cubensis (previously known as Diaporthe cubensis Bruner) in Africa and the Old World (Hodges et al. 1979; Hodges 1980). Hitherto, C. cubensis has been recorded from Cuba, Surinam, Brazil, Puerto Rico, Costa Rica and the U.S.A. (Florida and Hawaii), where it has caused serious loss to eucalypt plantations where conditions favoured attack.
THE DISEASE
C. cubensis is a primary pathogen of Eucalyptus spp. and has not been recorded on hosts outside this genus. It attacks the cambium and sapwood, causing a slight depression in the bark at first where the tissues have been killed. As the centre of infection spreads, the sapwood becomes stained brown and longitudinal cracks appear in the affected bark. Some exudation of gum may occur. A typical canker lesion eventually forms with dead tissues at the centre and a periphery with callus formation. Pycnidia and perithecia of the fungus form in bark cracks around the edge of this lesion which produce airborne spores by which the fungus is spread, mainly under wet conditions.
Trees between the ages of 2 and 8 years are generally most susceptible and may be killed by girdling when conditions favour multiple canker formation. Under conditions less favourable to infection serious damage may still arise through stem breakage and reduction in the capacity of stumps to coppice (Hodges and Reis 1974).
The growth of C. cubensis in culture has an optimum at 28–30°C and field attack is similarly favoured by temperatures over 23°C combined with high humidity and rainfall.
Eucalyptus spp. vary widely in their susceptibility to attack by C. cubensis, as shown in the classification below:
| Highly Susceptible | E. saligna |
| E. maculata | |
| Moderately Susceptible | E. grandis |
| E. alba | |
| E. propinqua | |
| E. tereticornis | |
| Moderately Resistant | E. robusta |
| E. microcorys | |
| E. paniculata | |
| Highly Resistant | E. citriodora |
| E. urophylla | |
| E. torelliana | |
| E. deglupta |
This rating is no more than approximate. Considerable variation can be found in susceptibility between provenances of the same species. The degree of attack sustained by the crop will, of course, depend on environmental conditions as well as the inherent reaction of the host (Ferreira et al. 1977).
CONTROL MEASURES
Management of this disease has been achieved very largely through selection for resistance combined with other desirable crop qualities within the species. Considerable advances have been made in this, and the clonal propagation of selections, by Brazilian workers in recent years.
REFERENCES
Ferreira, F.A.; Reis, M.S.; Alfenas, A.C.; Hodges, C.S. 1977 Avaliacao de Resistencia de Eucalyptus spp. ao cancro causado por Diaporthe cubensis Bruner. Fitopatologia Brasiliera 2:225–241.
Hodges, C.S.; Reis, M.S. 1974 A influencia do cancro basal causado por Diaporthe cubensis Bruner na brotacao de Eucalyptus saligna Sm. Brasil Florestal 5:25–28.
Hodges, C.S.; Ferreira, F.A.; Henfling, J.D.M. 1976 O Cancro do eucalipto causado por Diaporthe cubensis. Fitopatologia Brasiliera 1:129–170.
Hodges, C.S.; Geary, T.F.; Cordell, C.E. 1979 The occurrence of Diaporthe cubensis on Eucalyptus in Florida, Hawaii and Puerto Rico. Plant Disease Reporter 63:216–220.
Hodges, C.S. 1980 The Taxonomy of Diaporthe cubensis. Mycologia 72:542–548.
