Response of cybrids and a somatic hybrid of lemon to Phoma tracheiphila infections

The reaction of lemon hybrids obtained by symmetrical and asymmetrical prot oplast fusion, toward "mal secco" infection caused by Phoma tracheiphila (P etri) Kanc. et Ghik. was examined. Resistance was tested in 'Valencia' swee t orange [Citrus sinensis (L.) OSbeck] and 'Femminello' lemon [C. limon (L. ) Burm; f.] somatic hybrid and cybrids, by stem and leaf inoculation tests and by analysis of propagule-number of P. tracheiphila in the xylem of stem -inoculated plants. In general, the somatic hybrid and the cybrids showed a n intermediate degree of resistance, with slight differences in disease sym ptoms,in comparison with resistant 'Monachello' lemon and susceptible 'Femm inello' lemon; used as controls, The lower mortality in the asymmetrical le mon cybrids suggests that specific mechanisms of resistance to the disease could be activated in-these genotypes.