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Factors Related to Partial Resistance of Barley to Leaf Rust. G. D. Statler, Department of Plant Pathology, North Dakota State University, Fargo 58105; J. E. Parlevliet, Department of Plant Breeding (I.V.P.), Lawickse Allee, 166, Wageningen, The Netherlands. Phytopathology 77:549-551. Accepted for publication 8 August 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-549.

Several components of partial resistance were studied in three barley (Hordeum vulgare) cultivars known to be widely divergent in their reactions of partial resistance to Puccinia hordei. Uredinia were counted daily to determine infection density and latent period. Inoculated leaf samples taken daily were cleared and stained for fluorescent microscopy. The factors studied histologically included proportion of successful infection units, penetration, number of haustorial mother cells (HMC), early abortion, late abortion, colony size, and uredinium sporulating area. Latent period (LP50) was longer for the cultivars with partial resistance. Infection density and proportion of successful units was lower for cultivars with partial resistance. The average percentage of germinated urediniospores that had not penetrated was higher for the cultivar with the highest level of partial resistance (17-5-16) than for the very susceptible cultivar (L94). The percentage of early-aborted colonies was much higher for cultivars with partial resistance than for the susceptible cultivar. The percentage of late-aborted colonies was significantly greater for cultivar 17-5-16 than for the other cultivars. The average area of P. hordei colonies and the number of HMC was greater for the susceptible cultivar than for those with partial resistance. The size of the sporulating uredinium was not significantly different for any of the cultivars. The most definitive histological difference between susceptible and partially resistant barley cultivars to P. hordei was the amount of early abortion in the cultivars with partial resistance. The most important factor of partial resistance was the slower development of fewer sporulating colonies.