Cellular response of loblolly pine to wound inoculation with bark beetle-associated fungi and chitosan
We inoculated loblolly pines with bark beetle-associated fungi and a fungal cell wall component, chitosan, known to induce responses in some pines and many other plants. Trees in Florida were inoculated with Leptographium procerum, L. terebrantis, Ophiostoma minus, or chitosan. Trees in Louisiana were inoculated with O. minus, Entomocorticium sp. A, or Ceratocystiopsis ranaculosus. In both Florida and Louisiana, mechanical wounds served as controls. Treatment responses were sampled after 3 weeks, and all produced uniform responses across trees. Inoculations with E. sp. A and C. ranaculosus appeared similar to controls. Inoculations with L. procerum produced slightly higher levels of host damage. Loblolly pine responded similarly to chitosan and pathogenic bark beetle-associated fungi (O. minus and L. terebrantis), producing high levels of phenolic compounds and cell hydrolysis in the callus. In addition, callus inoculated with O. minus appeared extremely disrupted and "stringy." Chitosan inoculations resulted in no hydrolysis, but produced extremely high levels of phenolics deposition, as well as noticeable periderm formation. Our results reveal possible morphological mechanisms for pine secondary response to these fungi and suggest that chitosan may have potential as a stable material for testing variability in this response.