Is eucalyptus rust (Puccinia psidii) a threat?
A review (Coutinho et al., 1998) has recently been published on eucalyptus rust caused by Puccinia psidii (host plants, distribution, biology etc.). A remarkable feature of this disease is that it does not occur on eucalyptus in their centres of origin, but essentially in Central and South America. It apparently originated on native Myrtaceae in South America and was then able to attack eucalyptus there. Puccinia psidii was first described on Psidium pomiferum in Brazil in 1884. It was formally described on Eucalyptus citriodora in 1944 (although observations were already made in 1912) and the first serious outbreak occurred in 1973 in the state of Espirito Santo where losses were seen more particularly in eucalyptus nurseries and young plantations. Affected eucalyptus plants show golden yellow uredinial pustules on branches and terminal shoots as well as on young leaves. This rust rarely kills eucalyptus, except when it is found on coppice growth of highly susceptible eucalyptus. If trees are continuously re-infected they become stunted. This fungus has a macrocyclic life cycle and is considered as autaecious. It is reported that the presence of free water for more than 3 h and temperatures of 18°C to 23°C are favourable to uredial cycles, and that teliospore production is favoured by temperatures near 25°C. Urediniospores are spread by rain, insects and wind. For more details on the biology of the fungus refer to Coutinho et al., 1998. To control the disease, fungicides can be used (mancozeb, triadimenol, triforine, oxycarboxin, diniconazole) and resistant genotypes can be planted.
Host range
P. psidii is only reported on Myrtaceae, and a full list of known hosts is given by Coutinho et al., 1998. This rust can attack: Callistemon speciosus, Eucalyptus spp. (at least 14 species are reported), Eugenia spp., Melaleuca leucodendron, Pimenta spp., Psidium guavaja (guavas) and other Psidium spp., Syzygium jambos, Myrcia spp. It appears that there is some variability in host specificity, and it is suggested that some races or formae speciales might exist but this remains to be studied.
Geographical distribution
This geographical distribution is given on all hosts. Three isolated records of rust on Eucalyptus have been made in South Africa, Taiwan and India but no definitive species identifications could be made. These records remain unconfirmed.
Africa: South Africa (unconfirmed).
Asia: India (unconfirmed), Taiwan (unconfirmed).
North America: USA (south of Florida).
South America: Argentina, Brazil, Colombia, Ecuador, Paraguay, Uruguay, Venezuela.
Central America and Caribbean: Cuba, Dominican Republic, Jamaica, Puerto Rico, Trinidad.
The authors concluded that P. psidii represents a very serious threat to eucalyptus plantations in many parts of the world and that further studies on taxonomy, host range, life cycle and infection process are particularly needed
Sources
Coutinho, T.A.; Wingfield, M.J.; Alfenas, A.C.; Crous, P.W. (1998) Eucalyptus rust: a disease with the potential for serious international implications.
Plant Disease, 82(7), 819-825.