Quantitative-Genetic Basis of Aggressiveness of 42 Isolates ofFusarium culmorumfor Winter Rye Head Blight

Forty-two isolates of Fusarium culmorum obtained from diseased plant parts collected from fields in nine European countries and Australia were tested on a synthetic winter rye population. A spore suspension of each isolate was sprayed during midanthesis in five environments (location-year combinations) onto the heads. All isolates were pathogenic as judged by head blight rating scored on a 1 to 9 scale and grain weight relative to the noninoculated control. Isolates differed, however, in their ability to cause disease (aggressiveness). Quantitative geno-typic variation for aggressiveness occurred, while isolate-environment interaction variance, although significant, accounted for only 14% of total variance averaged over both traits. Correlations for aggressiveness across environments ranged from 0.6 to 0.8 (P = 0.01). Estimates of heritability on an entry-mean basis were high (h 2 = 0.9) for both traits, indicating that a substantial proportion of the phenotypic variation was caused by genetic effects. It is concluded that aggressiveness of F. culmorum is inherited as a complex trait.