Inheritance of resistance to leaf and glume blotch caused by Septoria nodorum Berk. in winter wheat

Sixteen crosses between eight winter wheat cultivars were screened for resi stance to Septoria nodorum leaf and glume blotch in the F-1 and F-4 generat ions using artificial inoculation in the field. The F-1 of most crosses sho wed dominance for susceptibility on both ear and leaf. The effects of gener al combining ability were of similar magnitude as the effects for specific combining ability. On the basis of the phenotypic difference of the parents , no prediction was possible about the amount and the direction of genetic variance in the segregating populations. The variation observed in this stu dy both within and among the segregating populations suggests a quantitativ e inheritance pattern influencing the expression of the two traits. The com ponents of variance between F-2 families within a population were as high a s (for S. nodorum blotch on the ear) or higher (for S. noderum blotch on th e leaf) than those between populations. Therefore, strong selection within a few populations may be as effective to obtain new resistant genotypes as selection in a large number of populations. In almost all crosses, progenie s were found that were more resistant than the better parent. Thus transgre ssion breeding may be a tool to breed for higher levels of resistance to S. nodorum blotch. Highly resistant genotypes were found even in combination with two susceptible parents. The genetic source for Septoria resistance is probably broader than is generally assumed and could be used to improve S. nodorum resistance by combination breeding followed by strong selection in large populations.