GENETIC CONTROL OF VIRULENCE IN USTILAGO HORDEI 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 F3 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 UhV1UhV1Uhv2Uhv2 were designated as UhR1 and Uhr1; those revealed by interactions with culture Uhv1Uhv1UhV2UhV2 were designated as UhR2 and Uhr2. The genotype UhR1UhR1Uhr2UhV2 was thus assigned to varieties Hannchen and Vantage and UhR1Uhr1UhR2UhR2 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.