Differential Changes in Host Specificity among MGR586 DNA Fingerprint Groups of Pyricularia Grisea

Instability of the Magnaporthe oryzae avirulence gene AVR-Pita alters virulence

“…Previously, diverse mutations of AVR-Pita have occurred in several laboratory strains of M. oryzae, allowing M. oryzae to avoid triggering the Pi-ta-mediated defense response (Kang et al, 2001;Orbach et al, 2000). This preclusion results in a race-shift from avirulence to virulence on rice cultivars previously exhibiting resistance to M. oryzae in a gene-for-gene fashion (Flor, 1971;Correll et al, 2000a). Our results show that insertion of Pot3 transposon into the coding region of AVR-Pita in isolate B2 might be responsible for inactivation of AVR-Pita function, and leading to the loss of rice blast resistance in Pi-ta-containing cultivars including Banks.…”

“…Isolate FL9 was recovered as a race-shift isolate from rice cultivar Katy grown in greenhouse. Isolates 1188R and 1188S as well as the isolates with a ''B'' prefix were collected from the cultivar Banks from several counties in Arkansas during severe rice blast epidemics in commercial fields in 2004. d 1 = Correll et al, 2000a;2 = Correll et al, 2000b;3 = Xia et al, 2000. e Cultivars Katy and Drew have the resistant Pi-ta allele, and cultivars C101A51 and M202 have the susceptible pi-ta allele (Jia et al, 2003); mean disease reactions of 0-2 on the 0-5 scale or 0-3 on the 0-9 scale were considered as resistant reactions (''R''), whereas reactions of 3-5 or 4-9 were considered as susceptible reactions (''S'').…”

“…Although field and greenhouse isolates of M. oryzae have been recovered that have been virulent on Pi-ta-containing cultivars since the mid 1990's (Correll et al, 2000a), no blast epidemics had been observed on any Pi-ta-containing cultivars in commercial production fields. However, in 2004, epidemics were observed on Banks in several fields in several different counties in Arkansas, USA .…”

“…The isolates include wild-type field isolates (WT); race-shift isolates (RS) which were virulent isolates on Pi-ta-containing cultivars that were originally recovered from the susceptible lesions on Katy after inoculated with a parental isolate which was avirulent on Katy (Correll et al, 2000a), and nitrate (nit) and sulfate (sul) non-utilizing mutants that were used as marked strains to confirm that the race-shift isolate originated from the avirulent parental isolate (Correll et al, 2000b). Isolate FL9 was recovered as a race-shift isolate from cultivar Katy grown in greenhouse.…”

Analysis of rice blast resistance gene Pi-z in rice germplasm using pathogenicity assays and DNA markers

“…An additional blast race will increase the complexity for R gene identification because it may contain a different avirulence gene because each AVR gene is sufficient to trigger the corresponding R gene mediated resistance. IB33 was a laboratory-generated strain (F. Lee, unpublished data); and IB49 was a field isolate; both of which were highly similar in fingerprinting (Correll et al 2000;Zhou et al 2007). If a pair of AVR/VIR cannot detect an R gene, it may suggest that there are R genes in rice that interfere with expected disease reactions.…”