Resistance of Salix Caprea, S. Phylicifolia, and Their F1 Hybrids to Herbivores and Pathogens. Hjältén, J., Ericson, L., & Roininen, H. 7(1):51–56.
abstract   bibtex   
Traits that make plants unpalatable to herbivores are often believed to have evolved as a response to herbivory. Thus, it has been suggested that the genetic re-combinations that occur when plants hybridize might result in a breakdown in plant resistance to herbivores and pathogens. In this study, we tested whether hybrid plants are less resistant to herbivores and pathogens than the parental species under controlled environmental conditions. Two common and widespread willow species, the tree-forming Salix caprea L. and the shrub-forming S. phylicifolia Sm. (L.) and their F1 hybrids were used in the study. To control the origin of plant material used in the experiments, we hand-pollinated plants in the field to create F1 hybrids and pure parental individuals, which were potted and kept outdoors in an experimental field. During the third growing season we measured plant survival, leaf numbers, and the densities of three species (gallers and leaf-folders of sub-genus Pontania and Phyllocolpa) of galling sawflies (Hymenoptera: Tenthredinidae) and the frequency of leaves infected by the parasitic fungus, Rhytisma salicinum. The experimental design used should minimize the influence of environmental variation on the plant characters. Therefore, the results primarily reflect genetically based differences in quality between hybrids and parental species. Hybrids and S. phylicifolia had more leaves than S. caprea. In addition, hybrids and S. caprea had higher densities of the leaf-galler Pontania pedunculi and the leaf-folder Phyllocolpa sp. than S. phylicifolia, whereas no differences were found between S. caprea and hybrids. We found little evidence suggesting a resistance breakdown in hybrids. Instead, the results are consistent with prediction from the dominance hypothesis, i.e. , similar herbivore load on hybrids and one of the parental species. The density of bean-galls (Pontania bridgmanii) and the frequency of leaves infected by the tar-spot disease, Rhytisma salicinum did not differ significantly between the plant categories. We conclude that to understand the mechanisms responsible for the disease/attack patterns on hybrid plants, the life cycle/life history traits of the involved organisms must be considered.
@article{hjaltenResistanceSalixCaprea2000,
  title = {Resistance of {{Salix}} Caprea, {{S}}. Phylicifolia, and Their {{F1}} Hybrids to Herbivores and Pathogens},
  author = {Hjältén, J. and Ericson, L. and Roininen, H.},
  date = {2000-03},
  journaltitle = {Ecoscience},
  volume = {7},
  pages = {51--56},
  issn = {0028-0798},
  abstract = {Traits that make plants unpalatable to herbivores are often believed to have evolved as a response to herbivory. Thus, it has been suggested that the genetic re-combinations that occur when plants hybridize might result in a breakdown in plant resistance to herbivores and pathogens. In this study, we tested whether hybrid plants are less resistant to herbivores and pathogens than the parental species under controlled environmental conditions. Two common and widespread willow species, the tree-forming Salix caprea L. and the shrub-forming S. phylicifolia Sm. (L.) and their F1 hybrids were used in the study. To control the origin of plant material used in the experiments, we hand-pollinated plants in the field to create F1 hybrids and pure parental individuals, which were potted and kept outdoors in an experimental field. During the third growing season we measured plant survival, leaf numbers, and the densities of three species (gallers and leaf-folders of sub-genus Pontania and Phyllocolpa) of galling sawflies (Hymenoptera: Tenthredinidae) and the frequency of leaves infected by the parasitic fungus, Rhytisma salicinum. The experimental design used should minimize the influence of environmental variation on the plant characters. Therefore, the results primarily reflect genetically based differences in quality between hybrids and parental species. Hybrids and S. phylicifolia had more leaves than S. caprea. In addition, hybrids and S. caprea had higher densities of the leaf-galler Pontania pedunculi and the leaf-folder Phyllocolpa sp. than S. phylicifolia, whereas no differences were found between S. caprea and hybrids. We found little evidence suggesting a resistance breakdown in hybrids. Instead, the results are consistent with prediction from the dominance hypothesis, i.e. , similar herbivore load on hybrids and one of the parental species. The density of bean-galls (Pontania bridgmanii) and the frequency of leaves infected by the tar-spot disease, Rhytisma salicinum did not differ significantly between the plant categories. We conclude that to understand the mechanisms responsible for the disease/attack patterns on hybrid plants, the life cycle/life history traits of the involved organisms must be considered.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13506708,herbivory,hybridisation,salix-caprea,species-resistance},
  number = {1}
}
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