Comparative genomic analyses have revealed extensive colinearity ingene orders in distantly related taxa in mammals and grasses, whichopened new horizons for evolutionary study. The objective of ourstudy was to assess syntenic relationships of quantitative trait loci(QTL) for disease resistance in cereals by using a model system inwhich rice and barley were used as the hosts and the blast fungusPyricularia grisea Sacc. as the pathogen. In total, 12 QTL against threeisolates were identified in rice; two had effects on all three isolates,and the other 10 had effects on only one or two of the three isolates.Twelve QTL for blast resistance were identified in barley; one hadeffect on all three isolates, and the other 11 had effects on only oneor two of the three isolates. The observed isolate specificity led to ahypothesis about the durability of quantitative resistance commonlyobserved in many plant host-pathogen systems. Four pairs of the QTLshowed corresponding map positions between rice and barley, twoof the four QTL pairs had complete conserved isolate specificity, andanother two QTL pairs had partial conserved isolate specificity. Suchcorresponding locations and conserved specificity suggested a commonorigin and conserved functionality of the genes underlying theQTL for quantitative resistance and may have utility in gene discovery,understanding the function of the genomes, and identifying theevolutionary forces that structured the organization of the grassgenomes.