II. Cereal disease: the interplay between resistance and pathogenicity: Inheritance of pathogenicity in Gaeumannomyces graminis var. tritici

Abstract

ABSTRACTThe purpose of the research was to discover whether pathogenicity in G. graminis is under major gene or multiple gene control and how pathogenic variation is generated in the field. The shoot dry weight of infected wheat seedlings was used as a measure of pathogenicity.Crosses were made between isolates differing in pathogenicity using a weakly pathogenic auxotrophic mutant requiring para‐aminobenzoic acid for growth as one of the parental isolates in each cross. A nuclear marker was necessary since G. graminis is homothallic. The mutation was produced by irradiating macerated hyphal strands with ultra‐violet light.Analysis of the progeny indicated that pathogenicity is under multiple gene control and that most of the genotypic variation is additive. There is a possibility of non allelic interactive effects but the evidence is not conclusive.The possibility of heterokaryosis in G. graminis was investigated by comparing pathogenicity between hyphal tip cultures and internal cell cultures derived from individual field isolates. Some field isolates were shown to be heterogeneous. In addition, heterokaryotic hyphae were synthesised between the mutant isolate and its parental wild‐type isolate. These results showed that potentially G. graminis could grow as a heterokaryon although how widespread this is in nature is not clear.