Powdery Mildew Resistance in Wheat Cultivar Mv Hombar is Conferred by a New Gene, PmHo

A new powdery mildew resistance gene designated as PmHo was identified in 'Mv Hombar' winter wheat, bred in Martonvasar, Hungary. It has exhibited a high level of resistance over the last two decades. Genetic mapping of recombinant inbred lines derived from the cross 'Ukrainka'/Mv Hombar located this gene on chromosome 2AL. The segregation ratio and consistent effect in all environments indicated that PmHo is a major dominant powdery mildew resistance gene. The race-specific nature of resistance in Mv Hombar was shown by the emergence of a single virulent pathotype designated as 51-Ho. This pathotype was, to some extent, able to infect Mv Hombar, developing visible symptoms with sporulating colonies. Microscopic studies revealed that, in incompatible interactions, posthaustorial hypersensitivity reaction was the most prevalent but not exclusive plant defense response in Mv Hombar, and fungal growth was mostly arrested during haustorium formation or in the early stages of colony development. The delayed fungal development of the virulent pathotype 51-Ho may be explained by additional effects of other loci that were also involved in the powdery mildew resistance of Mv Hombar.