VIEW ARTICLE

Resistance

Evidence of Differential Interaction in the Polygenic Hordeum vulgare-Puccinia hordei Relation during Epidemic Development. J. E. Parlevliet, Plant Breeding Department (I.v.P.), Agricultural University, Lawickse Allee 166, Wageningen, The Netherlands; Phytopathology 67:776-778. Accepted for publication 3 December 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-776.

The partial resistance of barley (Hordeum vulgare) to leaf rust (which is caused by Puccinia hordei) shows all characteristics of the so-called horizontal type of resistance. The partial resistance in the field, the latent period, and the infection frequency in young flag leaves were measured in three fairly resistant cultivars with five different isolates. The cultivars and the isolates differed significantly (P = 0.001) for all three variables. The cultivar-isolate interaction component was highly significant for latent period; the Julia-isolate 18 combination showed a differential interaction, but other combinations also contributed to the interaction variance. In the field, the partial resistance of the Julia-isolate 18 combination also appeared to interact differentially. The cultivar effect on latent period was shown earlier to be governed by polygenes. This indicates that differential interactions occur in a polygenic system and suggests that polygenic systems in the host can operate on a gene-for-gene basis with polygenic systems in the pathogen.