Effectiveness of the Wheat Blast Resistance Gene <i>Rmg8</i> in Bangladesh Suggested by Distribution of an <i>AVR-Rmg8</i> Allele in the <i>Pyricularia oryzae</i> Population

Abstract

Wheat blast caused by the <i>Triticum</i> pathotype of <i>Pyricularia oryzae</i> was first reported in 1985 in Brazil and recently spread to Bangladesh. We tested whether <i>Rmg8</i> and <i>RmgGR119</i>, recently identified resistance genes, were effective against Bangladeshi isolates of the pathogen. Common wheat accessions carrying <i>Rmg8</i> alone (IL191) or both <i>Rmg8</i> and <i>RmgGR119</i> (GR119) were inoculated with Brazilian isolates (Br48, Br5, and Br116.5) and Bangladeshi isolates (T-108 and T-109). Br48, T-108, and T-109 carried the eI type of <i>AVR-Rmg8</i> (the avirulence gene corresponding to <i>Rmg8</i>) while Br5 and Br116.5 carried its variants, eII and eII' types, respectively. Detached primary leaves of IL191 and GR119 were resistant to all isolates at 25°C. At a higher temperature (28°C), their resistance was still effective against the eI carriers but was reduced to a low level against the eII/eII' carriers. A survey of databases and sequence analyses revealed that all Bangladeshi isolates carried the eI type which induced a higher level of resistance than the eII/eII' types. The resistance of IL191 (<i>Rmg8</i>/<i>-</i>) to the eI carriers was maintained even at the heading stage and at the higher temperature. In addition, GR119 (<i>Rmg8</i>/<i>RmgGR119</i>) displayed higher levels of resistance than IL191 at this stage. These results suggest that <i>Rmg8</i> combined with <i>RmgGR119</i> will be useful in breeding for resistance against wheat blast in Bangladesh.