Conferring downy mildew (Pseudoperonspora humuli) resistance in hop (Humulus lupulus)
Hops are thought to be native to Asia. The three known hop species are Humulus lupulus, H. japonicus, and H. yunnanensis. H. lupulus is the only widely cultivated crop species of the three, although H. japonicus can be used ornamentally. Several subspecies exist within H. lupulus, which include a European, Japanese, common hop subspecies var. lupulus, and three native North American subspecies. The North American subspecies include var. neomexicanus, var. pubescens, and var. lupuloides; these represent Western North America, Midwestern USA, and Central and eastern North America (Small, 1980).