MOLECULAR ANALYSIS OF PHYTOPHTHORA DIVERSITY IN ORNAMENTAL NURSERIES.

A molecular approach based on the use of genus-specific nested-PCR primers (Scibetta et al., 2012; J. Microbiol. Meth. 88: 356-368) was utilized to detect Phytophthora species in soil and root samples of potted ornamentals, collected across Apulia and Calabria, Southern Italy. Analyzed samples comprised many plant species with different levels of symptoms of decline on the canopy and root rots. Extraction protocols were optimized to obtain DNA samples of appropriate quality from soil and roots. The analysis of sequences after cloning of nested-PCR amplicons enabled the identification of different Phytophthora species including P. nicotianae, P. cinnamomi, P. cryptogea, P. palmivora and P. niederhauserii. Interestingly, a higher level of intraspecific variability was detected within each Phytophthora species if compared with results of previous reports obtained using the same method in natural ecosystems. Although, the existence of PCR artifacts due to Taq DNA polymerase errors cannot be completely excluded, the detection of the same genotypes (commonly differentiated by one or few polymorphic nucleotides) in different soil and/or root samples, confirmed the reliability of results. As a consequence the higher intraspecific variability detected in ornamental nurseries seem to be the results of a more intensive sexual recombination favored by the concurrent cultivation of many plant species which increases the meeting of different genetically distant isolates of the pathogens.