Diversity of Phytoplasmas Infecting Fruit Trees and Their Vectors in Croatia

A survey started in 2002 (Križanac et al. 2008) was continued to determine the diversity of phytoplasmas infecting fruit trees and their vectors in Croatia. Leaf and twig samples from 32 commercial orchards located in all major fruit growing regions of Croatia, were visually inspected for symptoms and tested for the presence of the phytoplasma 16S rDNA as were adjacent symptomless wild Prunus species, and potential insect vectors from seven orchards. Phytoplasmas belonging to ‘ Candidatus Phytoplasma pyri’ and ‘ Ca . P. prunorum’ (riboso-mal subgroups 16SrX-C and 16SrX-B, respectively) were the most widespread and had the highest incidence in pears and stone fruits, respectively. ‘ Ca . P. asteris’ (16SrI-B) was found sporadically in both fruit trees and vectors, while phytoplas-mas of the stolbur group (16SrXII-A) was frequently found in pear. Mixed infections were detected in one pear and one Japanese plum. The high incidence and wide geographical distribution of stolbur phytoplasma in pears along with its presence in Cacopsyla pyri , the main vector of pear phytoplasma, calls for investigation of the role of this phytoplasma in the development of pear decline in Croatia. Cacopsylla pyrisuga , a suspected ‘ Ca . P. pyri’ psyllid vector, was also found to harbour stolbur phytoplasma. This study revealed higher phytoplasma diversity in fruit trees and vectors than anticipated.