Analysis of genetic diversity of SSR markers and avirulence genes in Magnaporthe oryzae populations from Italian rice fields.

The Ascomycete Magnaporthe oryzae is the causal organism of rice blast, the most serious fungal disease of rice worldwide. Italy is the first European rice producer (52%), but only a small portion of the Italian rice accessions was found to be resistant to blast disease, highlighting the need for implementation of rice breeding programs. The pathogen adapts to its host and new races can appear and attack resistant varieties breaking down the efforts to introduce resistance genes in rice. The knowledge of the genetic diversity and definition of the structure of existing populations is an useful information to select representative strains for resistance evaluation and to develop resistance deployment strategies. Magnaporthe genetic diversity has been already analyzed at the European scale. But, the Italian blast population was not studied in details both for its genetic and pathotypic diversity. Particularly, little is known about the avirulence genes present in Italian Magnaporthe isolates. The main goal of this study was to investigate the genetic diversity and pathogenicity of Italian M. oryzae strains to implement national rice breeding program for durable resistance towards Italian rice blast population. To this aim, the diversity and population structure of a Magnaporthe collection of more than 350 Italian strains was assessed by SSR analysis. Additionally 5 avirulence genes (avrPita, avrPik, avrPia, avrPii, avr-Pizt) were analyzed at the sequence level. All-together, these data were used to analyse the distribution of the avirulence gene polymorphisms within the genetic groups identified by SSR genotyping.