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Postpenetration Development of Puccinia coronata avenae in Slow- and Fast-Rusting Cultivars of Avena byzantina. 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 74:899-903. Accepted for publication 17 February 1984. 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, 1984. DOI: 10.1094/Phyto-74-899.

Development of Puccinia coronata in slow-rusting (Red Rustproof 14) and fast-rusting (Fulghum) cultivars of Avena byzantina was compared by using fluorescence microscopy. The first visible response was fluorescence in mesophyll cell walls of the slow-rusting cultivar. This reaction occurred about 18 hr after inoculation, and seemed to depend upon development of substomatal vesicles. The linear growth of hyphae in the slow-ruster was significantly less than in the fast-ruster 48 hr after inoculation. The growth of the parasite at individual infection sites in the slow-ruster was inversely related to the degree of host response, which was expressed as the number of fluorescing cells. A rapid and severe host reaction resulted in the arrest of growth of the parasite before haustorial mother cells formed, but slow host response merely retarded hyphal growth. The arrest of growth was associated with a reduction in the number of uredinia, while the retardation of hyphal growth reduced size of the uredinia and increased the latent period (LP50). Thus, fluorescence of the mesophyll cell walls was correlated with these three components of slow-rusting. In some sites, the host did not react to invasion by the parasite. When this happened, the hyphae grew at about the same rate in both cultivars. A few infection sites in the fast-rusting cultivar also exhibited a reaction in the mesophyll cells, but only 8% reacted quickly enough to arrest the growth of the parasite. Seven days after inoculation, the average area of the uredinia of the fast-ruster was about three times larger than that of the slow-ruster.

Additional keywords: horizontal resistance, reduced pustule number.