Identification of a candidate gene for the wheat endopeptidase Ep-D1 locus and two other STS markers linked to the eyespot resistance gene Pch1

Wheat is prone to strawbreaker foot rot (eyespot), a fungal disease caused by Oculimacula yallundae and O. acuformis . The most effective source of genetic resistance is Pch1 , a gene derived from Aegilops ventricosa . The endopeptidase isozyme marker allele Ep-D1b , linked to Pch1 , has been shown to be more effective for tracking resistance than DNA-based markers developed to date. Therefore, we sought to identify a candidate gene for Ep-D1 as a basis for a DNA-based marker. Comparative mapping suggested that the endopeptidase loci Ep-D1 (wheat), e np1 (maize), and Enp (rice) were orthologous. Since the product of the maize endopeptidase locus enp1 has been shown to exhibit biochemical properties similar to oligopeptidase B purified from E. coli , we reasoned that Ep - D1 may also encode an oligopeptidase B. Consistent with this hypothesis, a sequence-tagged-site (STS) marker, Xorw1 , derived from an oligopeptidase B-encoding wheat expressed-sequence-tag (EST) showed complete linkage with Ep - D1 and Pch1 in a population of 254 recombinant inbred lines (RILs) derived from a cross between wheat cultivars Coda and Brundage. Two other STS markers, Xorw5 and Xorw6 , and three microsatellite markers ( Xwmc14 , Xbarc97 , and Xcfd175 ) were also completely linked to Pch1 . On the other hand, Xwmc14 , Xbarc97 , and Xcfd175 showed recombination in the W7984 × Opata85 RIL population suggesting that recombination near Pch1 is reduced in the Coda/Brundage population. In a panel of 44 wheat varieties with known eyespot reactions, Xorw1, Xorw5 , and Xorw6 were 100% accurate in predicting the presence or absence of Pch1 whereas Xwmc14 , Xbarc97 , and Xcfd175 were less effective. Thus, linkage mapping and a germplasm survey suggest that the STS markers identified here should be useful for indirect selection of Pch1 .