Host specificity versus plurivority in barley leaf rusts and their microcyclic relatives

Abstract

The parasitic relations involving Puccinia hordei , heteroecious Uromyces rusts on Hordeum , and microcyclic Uromyces species on members of the Liliaceae and Amaryllidaceae are reported; the latter are putatively correlated with the heteroecious Uromyces rusts. In P. hordei , the dikaryotic stage is restricted to Hordeum spp. and the monokaryotic stage is compatible with Ornithogalum spp. Dipcadi erythraeum and Leopoldia eburnea . The latter stage is less parasitically specialized than the dikaryotic one. In heteroecious Uromyces rusts, uredinia and telia are formed on H. bulbosum, H. spontaneum and H. marinum but their monokaryotic stage radiates to a broader range of hosts, namely Bellevalia spp., Scilla spp., Muscari parviflorum and L. eburnea . Apparently, in contrast to P. graminis , the barley rusts have biogenetically radiated from the main to the alternate hosts. The microcyclic Uromyces species, presumably correlated with the heteroecious Uromyces rusts, are narrowly adapted to their source hosts in the genera Bellevalia, Scilla, Muscari and Pancratium . Only Urginea undulata and D. erythraeum are congenial with more than one microcyclic species, and L. eburnea is compatible with all tested rust species. It is noteworthy that all hosts with broader receptivity have originated in regions with less than 100 mm annual rainfall. The significance of this phenomenon and of the congeniality of L. eburnea with all listed rust species is discussed.