Genetic Structure of Pyricularia grisea (Cooke) Sacc. Isolates from Italian Paddy Fields

Abstract

Rice blast disease, caused by the fungus Pyricularia 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 a P. grisea population in the Po area, the largest rice area in Italy. Rice leaves showing blast symptoms were collected in three successive years (1998)(1999)(2000) and 43 P. grisea monoconidial culture samples were isolated from infected rice leaves. Fungal DNAs were obtained from mycelia. Moreover, six additional P. grisea DNA samples representative for the five characterized European lineages were also investigated. All 49 DNAs were fingerprinted using the Pot2-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.

Differential in vitro responses of rice cultivars to Italian lineages of the blast pathogen Pyricularia grisea. 2. Aromatic biosynthesis

“…In the case of blastsensitive genotypes, similar behavior was also observed for higher Cell wall hydrolysates were prepared from blast isolates belonging to the three main lineages found in Italy (Piotti et al, 2005), each one named with a different letter (A, B, C), and from one independent haplotype (D). Three days after subculturing, 50 mg L À 1 elicitor was added to cell cultures of 3 rice cultivars showing low (Gigante Vercelli) medium (Carnaroli) and high (Vialone nano) sensitivity to blast.…”

“…Hebert] Yaegashi & Udagawa), each isolated from a different rice cultivar, were used for elicitor preparation. DNA fingerprinting analysis allowed us to cluster them into the different lineages that were shown to be endemic to Italy (Piotti et al, 2005); strains named with the same letter belong to the same lineage. Elicitor fractions were obtained from the purified mycelial cell wall by thermal hydrolysis, as previously described (Roż kowicz et al, 2003).…”

“…DNA fingerprinting and pathotype analysis allowed the grouping of European blast populations into five discrete lineages (Roumen et al, 1997). Most Italian isolates were found to belong to three such groups (Piotti et al, 2005). On the other hand, significant variability exists in Italian rice germplasm with respect to blast sensitivity, ranging from highly resistant (Gigante Vercelli) to highly susceptible cultivars (Vialone nano and Maratelli) (Roumen et al, 1997;Kennedy et al, 2006).…”

Parasexual Recombination in Magnaporthe oryzae

“…This indicates that divergence among host genotypes may be related to the sexual or parasexual reproduction of this fungus. In areas of the United States and Europe, in contrast, simple population structures that appear to reflect clonal reproduction have been observed 43,50 . Don et al 14 a : Inoculation of the isolates was performed by press-injuring method on 6 th-leaf-stage plants.…”

Pathogenicity Analysis of Blast (Pyricularia oryzae Cavara) Isolates from West Africa

“…The disease has caused yield losses as high as 70 to 80%, when predisposing factors (high mean temperatures, relative humidity exceeding 90%, or the presence of dew, drought stress, or excessive nitrogen fertilization) favor epidemic development (Piotti et al 2005). Delassus (1973) reported rice yield losses of nearly 80% in West Africa.…”