Effects induced by fungal endophytes in Catharanthus roseus tissues infected by phytoplasmas

Endophytes are microorganisms (fungi, bacteria, actinomycetes) that live inside host plants without causing disease symptoms or apparent injury. Aureobasidium pullulans and Epicoccum nigrum are two endophytic fungi of particular interest because they are reported as antibiotic producers and antagonists against different phytopatogenic microorganisms. In this work, the cytological effects caused by endophyte-inoculation in phytoplasma-infected Catharanthus roseus tissues were investigated. Ultrastructural observations performed on leaves of endophyte-inoculated cuttings evidenced phytoplasma structural modifications associated with the increasing of host defence response, such as formations of phloem protein plugs, callose occlusions and presence of vacuolar phenolic depositions in the lumen of sieve elements. These modifications lead to the enhancement of physical barriers preventing the phytoplasma movements in the host.