RESUMO
Rmg8 and Rmg7 are genes for resistance to the wheat blast fungus (Pyricularia oryzae), located on chromosome 2B in hexaploid wheat and chromosome 2A in tetraploid wheat, respectively. AVR-Rmg8, an avirulence gene corresponding to Rmg8, was isolated from a wheat blast isolate through a map-based strategy. The cloned fragment encoded a small protein containing a putative signal peptide. AVR-Rmg8 was recognized not only by Rmg8, but also by Rmg7, suggesting that these two resistance genes are equivalent to a single gene from the viewpoint of resistance breeding.
Assuntos
Ascomicetos/patogenicidade , Resistência à Doença/genética , Genes Fúngicos , Genes de Plantas , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Triticum/genética , Triticum/microbiologia , Sequência de Aminoácidos , Sequência de Bases , Mapeamento Cromossômico , Folhas de Planta/microbiologia , Virulência/genéticaRESUMO
Blast, caused by Pyricularia oryzae, is one of the major diseases of wheat in South America. We identified a new gene for resistance to Triticum isolates of P. oryzae in common wheat 'S-615', and designated it "resistance to Magnaporthe grisea 8" (Rmg8). Rmg8 was assigned to chromosome 2B through molecular mapping with simple-sequence repeat markers. To identify an avirulence gene corresponding to Rmg8, Triticum isolate Br48 (avirulent on S-615) was crossed with 200R29 (virulent on S-615), an F1 progeny derived from a cross between an Eleusine isolate (MZ5-1-6) and Br48. Segregation analysis of their progeny revealed that avirulence of Br48 on S-615 was conditioned by a single gene, which was designated AVR-Rmg8. AVR-Rmg8 was closely linked to AVR-Rmg7, which corresponded to Rmg7 located on chromosome 2A of tetraploid wheat.
Assuntos
Interações Hospedeiro-Patógeno/genética , Fungos Mitospóricos/fisiologia , Triticum/genética , Mapeamento Cromossômico , Cromossomos de Plantas , Genes de Plantas , Imunidade Vegetal/genética , Poliploidia , Triticum/imunologiaRESUMO
In the process (BC3F1 generation) of backcrossing an Avena isolate of Pyricularia oryzae with a Triticum isolate, color mutants with white mycelia were obtained. These white mutants lacked virulence on all (31/31) hexaploid and most (28/32) tetraploid wheat lines tested. In a BC4F1 population, white and black cultures segregated in a 1:1 ratio, suggesting that the mutant phenotype is controlled by a single gene. Furthermore, the mycelial color was perfectly linked with avirulence in the BC4F1 population; white cultures were all avirulent on common wheat (Triticum aestivum) 'Norin 4' (N4) whereas black cultures were all virulent. White cultures in the BC3F1 and BC4F1 generations were also avirulent on tetraploid wheat (T. dicoccoides) accession 'KU109' (Tat4), which was susceptible to all cultures derived from the parental wild isolates through the BC2F1 generation. A cross between Tat4 and a susceptible tetraploid (T. paleocolchicum) accession 'KU196' (Tat14) produced resistant and susceptible F2 seedlings in a 3:1 ratio against the white cultures. In the F3 generation homozygous resistant/segregating/homozygous susceptible lines segregated in a 1:2:1 ratio. These results suggest that the resistance of Tat4 to the white cultures is controlled by a single major gene. This gene, tentatively designated as RmgTd(t), is considered to be a hidden resistance gene because it was not detected with the Br58, F1, BC1F1, or BC2F1 cultures. Cytological analysis revealed that the moderate resistance controlled by RmgTd(t) was associated with a hypersensitive reaction of mesophyll cells.
