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Rice blast disease, caused by Pyricularia oryzae Cavara, is considered the most destructive rice disease in Italy. Quinone outside inhibitor (QoI) fungicides are widely adopted for rice blast control, and their exclusive use poses a high risk for the development of resistances. Considering the extensive use of QoI fungicides in recent years, the aim of the study was to monitor azoxystrobin sensitivity in Italian P. oryzae populations, collected from different rice relevant areas. Ninety-nine isolates of P. oryzae, collected in 2020 from 32 commercial Italian rice fields, were grown in Petri dishes and tested for resistance through a two-discriminatory dose assay. Resistant isolates were detected in 6 rice samples coming from three Italian provinces (Pavia, Novara, Vercelli). The resistant isolates showed EC50 value > 100 mg/l azoxystrobin and resistance factors greater than 500. The molecular analysis of the cytochrome b gene confirmed the mutation of glycine to alanine at the 143 codon position (G143A) in the resistant strains. To our knowledge, this is the first report of QoI resistance of P. oryzae isolates from rice in Italy and highlight the importance to adopt proper anti-resistance strategies. [ABSTRACT FROM AUTHOR]

Rice blast disease, caused by the fungusPyricularia grisea(Cooke) Sacc., is responsible for considerable damages in rice crops in Italy and in other parts of the world. This study was conducted in order to investigate the genetic structure of aP. griseapopulation in the Po area, the largest rice area in Italy. Rice leaves showing blast symptoms were collected in three successive years (1998–2000) and 43P. griseamonoconidial culture samples were isolated from infected rice leaves. Fungal DNAs were obtained from mycelia. Moreover, six additionalP. griseaDNA samples representative for the five characterized European lineages were also investigated. All 49 DNAs were fingerprinted using thePot2-based repetitive polymerase chain reaction specific for the blast pathogen. Unweighted pair-group method with arithmetic averages cluster analysis shows the presence of three main Italian lineages. Within lineages, similarity was higher than 80%. Samples representative of the three of five known European lineages grouped within these three Italian lineages confirming the presence of three European lineages in Italy. Furthermore, cluster analysis shows the presence of two new haplotypes never found before in the Italian lineage. [ABSTRACT FROM AUTHOR]