Olive tree shoot proliferation: biochemical alterations and phytoplasma concentration in infected varieties

In Brazil, a disease known as olive tree shoot proliferation is associated with the presence of a phytoplasma belonging to the 16SrVII-B subgroup. This disease has negatively affected production by interfering with the normal development of infected plants. Control measures are essentially limited to planting pathogen-free seedlings and eradication of diseased plants. The interaction between host and pathogen is still poorly understood and this investigation aimed to determine biochemical changes induced by the pathogen and to evaluate its concentration in infected plant tissues. Leaves from the cultivars Arbequina, Arbosana, Grappolo and Koroneiki were sampled from plants experimentally infected with the pathogen using a grafting technique. Biochemical alterations were measured by specific methods and phytoplasma concentration was estimated by quantitative PCR. The results revealed that the pathogen concentration ranged among cultivars, suggesting a higher level of tolerance for the Arbequina cultivar, followed by Grappolo, Arbosana and Koroneiki. The biochemical changes in infected plants were characterized by alteration in total chlorophyll, reducing sugars and total proteins for cultivars Arbequina, Arbosana and Koroneiki, while cultivars Grappolo and Arbosana presented changes in the content of free and bound phenols.