Phenolic glycosides and condensed tannins in Salix sericea, S. eriocephala and their F1 hybrids: not all hybrids are created equal.

The performance of hybrids depends upon the inheritance and expression of resistance traits. Secondary chemicals are one such resistance trait. In this study, we measured the concentrations of phenolic glycosides and condensed tannins in parental and F1 hybrid willows to examine the sources of chemical variation among hybrids. S. sericea produces phenolic glycosides, salicortin and 2'-cinnamoylsalicortin, and low concentrations of condensed tannin in its leaves. In contrast, S. eriocephala produces no phenolic glycosides but high concentrations of condensed tannins in its leaves. These traits are inherited quantitatively in hybrids. On average, F1 hybrids are intermediate for condensed tannins, suggesting predominantly additive inheritance or balanced ambidirectional dominance of this defensive chemical from the parental species. In contrast, the concentration of phenolic glycosides is lower than the parental midpoint, indicating directional dominance. However, there is extensive variation among F1 hybrids. The concentration of tannin and phenolic glycosides in F1 hybrid families is either (1) lower than the midpoint, (2) higher than the midpoint, or (3) indistinguishable from the midpoint of the two parental taxa. It appears that the production of the phenolic glycosides, especially 2'-cinnamoylsalicortin, is controlled by one or more recessive alleles. We also observed a two-fold or greater difference in concentration between some hybrid families. We discuss how chemical variation may effect the relative susceptibility of hybrid willows to herbivores.