Diversity and Geographical Distribution of Phytoplasmas infecting China-tree in Argentina

Barley-pathogenic Pyrenophora isolates are P. graminea (PG), P. teres f. maculata (PTM) and P. teres f. teres (PTT), which cause foliar leaf stripe, spot blotch and net blotch lesions, respectively. However, the species are often indistinguishable by morphological and cultural characteristics. Random amplified polymorphic DNA (RAPD) analysis has been used to study the genetic relationship amongst 11 PG, 9 PTM and 23 PTT isolates from distant geographical locations. Using seven primers, 55 (52.38%) polymorphic DNA bands were detected out of 105 different fragments amplified in the three pathogens. Genotypic diversity was high as all but two PTT strains had distinct multilocus RAPD fingerprints. Unweighted pair-group method with arithmetic average (UPGMA) clustering separated the isolates into three main clusters, corresponding to the three pathogens studied. No clear geographical substructuring was found. Nei’s gene diversity analysis detected only small differences (max. 6.6%) in band frequencies but considerable levels of differentiation were observed among the pathogen species/forms. However, the variability among the Pyrenophora species/ forms (max. 42.0%) was less than within species/ forms (max. 58%). Nei’s unbiased genetic distance values were in agreement with UPGMA clustering and gene diversity analysis: the two forms of P. teres showed higher divergence from one another (D ¼ 0.132) than the distance found between PG and PTM (D ¼ 0.094). The results suggest that the present taxonomical classification of these morphological taxa may not correspond to their phylogenetic relationship and that there is a very close genetic relationship amongst barley-pathogenic Pyrenophora species, but genetic exchanges between them could be infrequent.