Mlo Resistance to Powdery Mildew (Blumeria graminis f. sp. hordei) in Barley Landraces Collected in Yemen

Barley (Hordeumvulgare L.) is one of the most important cereal crops in the world. Powdery mildew on barley, which is caused by the pathogen Blumeria graminis f. sp. hordei, occurs world-wide and can result in severe yield loss. Thousands of barley accessions are stored in national gene banks, and their characterization for breeding purposes is needed. This study was conducted to determine the resistance to powdery mildew in 33 barley landraces from Yemen, which were obtained from the ICARDA gene bank. Twenty differential isolates of barley powdery mildew were used. Nine single plant lines were selected from five landraces, based on tests that were performed with 30 plants per landrace, after inoculation with the most avirulent isolate of barley powdery mildew available. Two of these landraces originated from the Al Bayda province in Yemen, and three others originated from Dhamar, Sanaa, and Taizz, respectively. Next, single plant lines were tested using a set of 20 differential isolates of powdery mildew. Two lines that were selected from landrace from the Al Bayda province in Yemen, showed disease reaction designated as 0(4), which is specific for the presence of Mlo resistance. The new source of highly effective Mlo powdery mildew resistance that is described in this study could be used in barley breeding programs.