QUANTITATIVE-GENETIC BASIS OF AGGRESSIVENESS OF 42 ISOLATES OF FUSARIUM-CULMORUM FOR WINTER RYE HEAD BLIGHT

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