Mal secco disease of citrus
Mal secco, caused by Phoma tracheiphila, is a Mediterranean citrus disease absent from citrus-growing areas elsewhere in the world, and also from Spain (despite erroneous earlier reports). A study of coelomycetes on lemon in Spain (i.e. of pycnidial fungi resembling P. tracheiphila) led to isolation of species of Phoma, Diplodia, Phomopsis and Ascochyta. None were pathogenic when tested. Thus, non-pathogenic fungi resembling P. tracheiphila may be found on lemon - but the mal secco pathogen is not known in Spain and has never occurred there.
In Italy, an evaluation was made of the possible role of lemon fruits and seeds in spreading mal secco. Although fruits can be infected, such fruits mostly fall before harvesting. Latently infected fruits could possibly be marketed, but sporulation on them is unlikely.
Seeds from infected fruit can carry the fungus on the seed-coat, but tests show that it does not pass to the seedling on germination. As an extra precaution for countries using mal secco susceptible rootstock seedlings, a hot-water treatment of seeds (52°C for 10 min) is suggested.
Sources
Garcia J., Velasquez T. & Alfaro J.A. Coelomycete prospection of lemon fruit peels in Spain. Proceeding of the 7th Congress of the Mediterranean Phytopathological Union, Granada (ES), September 1987 p. 173.
lppolito A., De Cicco V., Cutuli G. & Salerno M. The role of infected citrus fruits and seeds in the spread of mal secco disease. Proceeding of the 7th Congress of the Mediterranean Phytopathological Union, Granada (ES), September 1987.