Document: ROB-3-43-13

Resistance of F₂ and backcross willow hybrids to herbivores.

FRITZ, R.S.* and C.G.HOCHWENDER

Vassar College, Poughkeepsie, NY 12604 USA ¹

Abstract:
Resistance of F₂ and backcross hybrids between Salix sericea and S. eriocephala were compared to pure parents and to F₁ hybrids. Five replicate crosses of parental and hybrid plants were made from pure parents. Plants were grown in pots in a common garden adjacent to naturally occurring willows. Leaf number and the numbers of gall-inducing, leaf-mining, leaf-tying and free-feeding herbivores were counted on the shoots of each plant to determine density. Data were analyzed with ANOVA and a priori contrasts. Contrary to the prediction that F₂ hybrids would have a higher breakdown in resistance than F₁ plants, we found four cases where F₂ plants were more resistant than F₁ plants. This suggested that recombination led to the breakup of host recognition traits in F₂ hybrids. Two cases showed the expected breakdown of resistance in F₂ plants. Comparing backcross plants to their parents, we found mostly additive inheritance of resistance or no difference among the taxa. In several cases, we found dominance of resistance or greater resistance in the backcrosses. This latter result also suggests the breakup of genes used for host recognition by these herbivores. For most herbivores, the inheritance of resistance in backcrosses differed depending on the direction of the backcross. These data indicate that hybridization may produce plants that are more resistant than their parents, contrary to the prediction that hybrids should be more susceptible.

Keywords: herbivores, hybrid plants

This abstract is being presented at: 3:15 PM in session:
Oral Session #48: Anti-Predator Responses: Fish to Sagebrush.