Fine Genetic and Physical Mapping of Powdery Mildew Resistance Gene MlIW170 derived from Wild Emmer

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a serious foliar disease of wheat affecting grain yield and end-use quality worldwide. Developing resistant wheat cultivars is the most effective and economical method to prevent this disease at present. So far, more than 40 wheat powdery mildew resistance loci have been identified. However, the emergence of new virulent pathogen races often leads to many resistance genes losing their resistance or reducing resistance. Identification and effective utilization of new powdery mildew resistance genes become necessary for disease resistance breeding program.

A fine genetic linkage map of semi-dominant powdery mildew resistance gene MlIW170, originated from wild emmer, was constructed with nine SSR markers and seven SCAR markers converted from AFLP markers. MlIW170 was physically mapped on bin 0.84-1.00 of chromosome 2BS using Chinese Spring nullisomic-tetrasomic, ditelosomic and deletion lines.

Comparative genomics analysis revealed the genomic region containing MlIW170 on 2BS showed high levels of collinearity with short arms of chromosome 5 of Brachypodium and chromosome 4 of rice. Five new EST-STS markers were developed and closely linked to MlIW170. Fine genetic linkage map of MlIW170 was constructed using a mapping population containing 1772 F₂ plants derived from a cross between susceptible durum wheat line 81086A and resistant emmer wheat line IW170. MlIW170 was flanked by SCAR marker XcauG3 and EST-STS marker XP2430 with genetic distance of 0.169cM and 0.113cM, respectively. SCAR marker XcauG3 was used to screen BAC library of durum wheat cultivar Langdon. Two overlapping positive BAC clones were sequenced and three RGA markers, one SSR marker, and one RJM marker linked to MlIW170 were developed according to the BAC sequences. Positive BAC clones were fingerprinted to construct the physical map and towards the map based cloning of the powdery mildew resistance gene MlIW170.