Selection for rice blast resistance is a major problem in any rice (Oryza sativa) breeding program due to the variability of the fungus Pyricularia grisea. This diversity has been characterized by DNA molecular markers and by virulence of the isolates that has been demonstrated on rice genotypes with different blast resistance genes. Molecular markers allow the identification of groups of isolates, so called lines, genetically related to each other, and the isogenic lines (NILs) in groups of virulence with the same or similar virulence pattern. The objectives of this work were to verify the molecular and virulence patterns from isolates of P. grisea from the State of Rio Grande do Sul. The DNA from 51 monosporic isolates obtained in Rio Grande do Sul were used in PCR reactions with primers based on the repetitive sequence Pot2. The same isolates were also used to inoculate six NILs. The statistical analysis indicates the presence of six lines and seven virulence groups. The frequency of virulent isolates is higher in the NIL that contains the Pi-1 allele and lower in the NIL containing the Pi-2 allele. The compatible reaction on the NIL that carries Pi- 2 is very weak, exhibiting, in general, a type 4 reaction. No obvious relationship between phenotypic virulence and line determination has been found.
