Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/1997
Publication Date: N/A
Interpretive Summary: Leaf rust is one of the most serious diseases of wheat, both in the United States and in other wheat-growing areas of the world. The disease is caused by a highly specialized fungus that often keeps ahead of the efforts of plant breeders to produce wheats resistant to it. The fungus attacks not only bread and pasta wheats grown by farmers, but also several wild relatives of wheat. In turn, there are leaf rust fungi on wild wheats, but no one has understood how these rust fungi relate to the leaf rust on wheat grown for food. The research in this paper shows clearly that the leaf rusts on wild wheat usually do not attack cultivated wheats and differ in so many characteristics that they are distinct species, different from the species usually attacking farmers' fields. This research was done cooperatively between scientists in the United States and in Israel, where wild wheats grow naturally. The results allow plant disease scientists to better understand the distinct features of the leaf rust attacking cultivated wheat. This will help the scientists develop better ways to control wheat leaf rust disease.
Technical Abstract: Aecial and telial host range, interfertility, teliospore dimensions, and amount of nuclear DNA were determined for Puccinia recondita collected either worldwide from species of cultivated wheats and rye, or in Israel from wild emmer for four species of wild wheat(Aegilops). The results indicate that the collections belong in two major groups: Group I(from cultivated wheats and wild emmer) which has Thalictrum speciosissimum as aecial host; and Group II (principally from wild wheats or rye) which has several species in the Boraginaceae as aecial host. In glasshouse experiments, intercrosses could be made readily among collections within Groups I and II but not between the two groups. Group I consisted of all collections from T.aestivum, T. turgidum var. dicoccoides, and most collections from T. turgidum var. durum. Group II consisted of four types, all clearly different from Group I. Type A was from T. turgidum var. durum found in fields near Anchusa italica. Type B was from Ae. ovata and had Echium glomeratum, Anchusa undulata, and Lycopsis arvensis as aecial hosts. Type C was from Ae. longissima, Ae. sharonensis, and Ae. variabilis and had A. aggregata, A. undulata and L. arvensis as aecial hosts. Type D was from Secale cereale and had Lycopsis arvensis and Anchusa undulata as aecial hosts. Teliospores were wider and larger in cross sectional area and nuclear DNA content was 1.3-1.6 times greater in Group II than in Group I. The results suggest that Groups I and II have evolved separately for an extended period and are now morphologically distinct and genetically isolated from each other. The subgroups within Group II are more closely interrelated but also show genetic divergence.