Host/nonhost status and genetics of resistance in barley against three pathotypes of Magnaporthe blast fungi

Blast disease, caused by the Magnaporthe oryzae/grisea species complex, occurs in a wide range of wild and cultivated gramineous plant species including rice, wheat and barley. We inoculated a collection of cultivated (Hordeum vulgare ssp. vulgare L.) and wild (ssp. spontaneum) barley accessions with M. oryzae Oryza pathotype (MoO), Triticum pathotype (MoT) and Pennisetum pathotype (MsP) to quantify the host status of barley, and to identify sources of blast resistance. Unlike wheat, the barley gene pool is rich with sources of complete and partial resistance against Magnaporthe. Cultivated barley appeared a nonhost to MsP, whereas wild barley showed some degree of susceptibility. All 153 tested rice accessions were resistant to the MoT isolate, suggesting that rice is nonhost to this pathotype. Inoculation of L94/Vada and Vada/SusPtrit RIL mapping populations with MoO and/or MoT isolates of M. oryzae indicated one large effect QTL, designated as Rmoq1, on the short arm of chromosome 7H against the MoT isolate PY 67.1 in both populations. Resistance in L94 to the MoO isolate was due to a different QTL, located at 5H. An association mapping panel of West European barley cultivars also suggested that most QTLs were pathotype specific. Six blast resistance genes found in the biparental and association mapping studies coincided with map positions of powdery mildew resistance genes viz. Mlt, Mla6, Mlg, mlo, Mlj, and Mlhb genes. Our QTL and association mapping analyses do not support the association of the mlo resistance gene with enhanced susceptibility to M. oryzae as reported in literature.