VARIATION AND COVARIATION FOR QUANTITATIVE RESISTANCE TO HEAD BLIGHT (FUSARIUM-CULMORUM) IN 2 TESTCROSS SERIES OF S-2 LINES IN WINTER RYE

The amount of genetic variation among inbred lines and testcrosses, an d covariation between both genetic materials, are of crucial importanc e for selection efficiency in hybrid breeding. To estimate these quan titative genetic parameters for resistance of winter rye (Secale cerea le) to head blight caused by Fusarium culmorum, 88 three-way cross hyb rids, produced by crossing each of 44 S-2 Carsten inbred lines with tw o unrelated Petkus single-cross testers, were evaluated along with the parental lines over 2 years. Resistance traits were head-blight ratin g and grain weight per spike relative to the non-inoculated control. S ignificant genotypic variation occurred among lines and in both testcr oss series. S-2 lines displayed considerably more variation than testc ross series. Genotype x environment interaction was more marked among the inbred lines, while estimates of heritability were similar for bot h genetic materials. Testcrosses showed heterosis for head-blight resi stance. No relationship existed between S-2 lines and the two testcros s series for any resistance trait. This might be caused by an associat ion between inbreeding and Fusarium-head-blight susceptibility and dif ferent inbreeding depression among the S-2 population. The phenotypic correlations between the testcross series were moderate for both trait s (r = 0.58, P < 0.01). In conclusion, Fusarium-head-blight resistance has to be selected at the respective heterozygosity levels.