VIEW ARTICLE

Resistance

Xenoparasite-Nonhost Reactions in Puccinia-Gramineae Pathosystems. H. H. Luke, Research plant pathologist, U.S. Department of Agriculture, ARS, Plant Pathology Department, University of Florida, Gainesville 32611; R. D. Barnett(2), and P. L. Pfahler(3). (2)Professor of agronomy, North Florida Research and Education Center, Rt. 3, P.O. Box 638, Quincy 32351; (3)Professor, Agronomy Department, University of Florida, Gainesville 32611. Phytopathology 77:1488-1491. Accepted for publication 1 May 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/Phyto-77-1488.

Histological studies of six species of Gramineae inoculated with five species of Puccinia were conducted to determine the kinds of defense systems involved in xenoparasite-nonhost interactions. Although all nonhost types had active (physiological) defense mechanisms, two exhibited quasi exclusion, but the few xenoparasites that penetrated stimulated a physiological response similar to specific resistance. Histological responses associated with cessation of fungal growth included fluorescent-collapsed mesophyll cells (specific resistance), fluorescent-noncollapsed (nonspecific resistance), and a nonfluorescent-noncollapsed type (unknown). These three defense mechanisms were observed in a single leaf of a nonhost plant inoculated with a pure race of a xenoparasite. Nonhost reaction types were clear cut, independent, and easily distinguished one from the other. The nonhost had specific and nonspecific resistance to most of the xenoparasites, indicating that these two types of resistance had a common origin. Another histological response was characterized by fluorescent-collapsed cells that did not retard radial growth of the hyphae. This reaction reduced haustorial mother cell formation and inhibited development of macroscopic symptoms in the nonhost. The nonhosts used in our study had five defense mechanisms, four physiological and one quasi exclusion type.