GENETIC CONTROL OF VIRULENCE IN <i>USTILAGO HORDEI</i> III. IDENTIFICATION OF GENES FOR HOST RESISTANCE AND DEMONSTRATION OF GENE-FOR-GENE RELATIONS

Abstract

The genetics of resistance of three barley varieties, Excelsior (E), Hannchen (H) and Vantage (V), was investigated against two known virulence genes (Uhv-1 and Uhv-2) present in two test cultures of Ustilago hordei. Segregations obtained from F 3 progenies derived from crosses EXH and EXV revealed that resistance and susceptibility to the two test cultures were inherited independently of one another; the resistance was expressed as a dominant characteristic at both loci. The host alleles discovered through the interactions with culture UhV 1 UhV 1 Uhv 2 Uhv 2 were designated as UhR 1 and Uhr 1 ; those revealed by interactions with culture Uhv 1 Uhv 1 UhV 2 UhV 2 were designated as UhR 2 and Uhr 2 . The genotype UhR 1 UhR 1 Uhr 2 UhV 2 was thus assigned to varieties Hannchen and Vantage and UhR 1 Uhr 1 UhR 2 UhR 2 to variety Excelsior. The interrelationships between two loci for resistance in the host and the two corresponding loci for virulence in the pathogen thus lead us to conclude that a gene-for-gene relationship also exists in the Hordeum vulgare: Ustilago hordei system.