Genetic linkage map of Phaeosphaeria nodorum, the causal agent of stagonospora nodorum blotch disease of wheat

Abstract

A genetic linkage map of the fungal pathogen Phaeosphaeria nodorum, the causal agent of stagonospora nodorum blotch disease of wheat, was created. A total of 152 ascospore-derived progeny from a single pseudothecium, which resulted from a cross of two opposite mating type isolates, Sn37-1 and S-81-B13B, was analysed with AFLP, RAPD, ISSR, expressed sequence tag (EST)-derived microsatellite primers and sequence tagged site markers developed from specific genes. The genetic linkage map consisted of 276 molecular markers, and included markers developed from five genes [Glyceraldehyde 3-phosphate dehydrogenase (gpd), malate synthase (Mls1), mannitol 1-phosphate dehydrogenase (Mpd1), mating type (MAT1) and RNA polymerase II (RPB2)], which were assigned to 21 major linkage groups (LGs). The total length of the 21 major LGs was 1,932.1 centiMorgans (cM) with an average spacing of 6.88 cM between loci. The idiomorph mating type gene (MAT1) loci was placed in LG 2 and was closely linked to RAPD marker A4-680. On the other hand, 24 molecular markers and four gene loci [β-glucosidase (bgl1), histidinol dehydrogenase (Hdh2), mannitol 1-phosphate dehydrogenase (Mpd2), and xylanase (Xyl 10-2)] were dispersed in 11 minor LGs. The segregation ratio of the xylanase (Xyl 10-1) locus was distorted and not mapped. This is the first genetic linkage map reported for this important foliar pathogen of wheat. In combination with the genomic sequence of P. nodorum strain SN15 (www.broad.mit.edu), the availability of a genetic linkage map of this organism would be an important tool to investigate quantitative trait loci (QTL) of biologically important phenotypes and for positional cloning.