Phoma tracheiphila (Mal secco).

P. tracheiphila is a conidial fungus causing serious damage and death to the host, particularly lemon [Citrus limon], in Citrus and related genera, in Mediterranean countries and the Black Sea region. So far, however, it is unknown in Spain, Portugal and Morocco, as well as other major citrus-growing regions of the world. This fungus is of concern to many international plant protection organizations and must be prevented from being spread in infected propagative material. It was once reported as seedborne in lemon, but there is no further evidence of this means of transmission. Once in the orchard, the fungus can be carried as spores from pycnidia and from hyphae on the plant and on fallen debris by rain, wind and irrigation water, and perhaps by birds and insects.

OXIDATIVE ENZYME RESPONSES OF SIX CITRUS ROOTSTOCKS INFECTED WITH PHOMA TRACHEIPHILA (PETRI) KANTSCHAVELI AND GIKASHVILI

SUMMARYCitrus trees are often exposed to severe infectious diseases. Mal secco caused by Phoma tracheiphila (Petri) Kantschaveli and Gikashvili is one of the most destructive fungal diseases of lemons (Citrus limon Burm. F.). In the present study, antioxidant enzyme activity in different mal secco-resistant and susceptible citrus rootstocks including Cleopatra mandarin (C. reshni Tan.), sour orange (C. aurantium L.), rough lemon (C. jambhiri Lush.), Volkameriana (C. volkameriana Tan. and Pasq.), Carrizo citrange (Poncirus trifoliata L. Raf. X C. sinensis L. Osbeck) and trifoliate orange (P. trifoliata) was investigated. Possible differences in constitutive levels of these antioxidant enzymes and correlations between enzyme levels and mal secco caused by P. tracheiphila were examined. Among the rootstocks, Cleopatra mandarin was found to be resistant to mal secco, whereas rough lemon, sour orange and trifoliate orange were highly susceptible. Total peroxidase (TPX; EC: 1.11.1.7) activity increased in all infected rootstocks. Ascorbate peroxidase (APX; EC: 1.11.1.11) activity increased in most of the rootstocks and no correlation was found between catalase (CAT; EC: 1.11.1.6) activity and mal secco resistance. This study indicates that overall TPX activity is upregulated and APX activity is up- and down-regulated depending on the type of rootstock in response to P. tracheiphila infection.