Submitted to: Symbiosis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 1997
Publication Date: N/A
Interpretive Summary: This paper reports results from greenhouse studies investigating the relationship between hormone (IAA and ethylene) production by mycorrhizal fungi and conifer seedling growth responses to inoculation with these fungi. Fungi with varying capabilities of hormone production were used to inoculate Douglas-fir, Lodgepole Pine and Englemann Spruce seedlings. Seedling growth responses varied with tree species and mycorrhizal fungus combination. The ability of the fungus to produce IAA was found to be related to the level of IAA detected in the roots of inoculated Douglas- fir seedlings. Levels of IAA in Douglas-fir roots ere correlated with some Douglas-fir growth response. The ability of the fungus to produce ethylene was not found to be related to Douglas-fir growth responses. The IAA content of inoculated Douglas-fir, Englemann Spruce and Lodgepole Pine was found to be strongly linked to the ability of the mycorrizal fungus to produce ethylene. These results suggest that a relationship exist between the production of auxin and ethylene by ectomycorrhizal fungi and changes in IAA content of roots that could affect growth responses of conifer seedlings.
Technical Abstract: To assess the relationship between in vitro growth regulator production by mycorrhizal fungi and plant growth responses in symbiosis, ectomycorrhizal fungi were characterized by their in vitro IAA and ethylene production capacity (quantified using HPLC and GC-MS methodology). The characterized fungi were used to inoculate 8-week-old Douglas-fir (Pseudotsuga menzesii (Mirb.) Franco.), Englemann Spruce (Picea englemannii Parry) and Lodgepole Pine (Pinus contorta Dougl.) seedlings maintained under glasshouse conditions. For six months after inoculation, seedlings were evaluated for changes in morphology and endogenous IAA content to determine any correlations between fungal IAA and ethylene production potential and plant responses. Morphological responses varied with tree species and mycorrhizal fungus combination. In vitro fungal IAA production was significantly correlated with endogenous root IAA content and many morphological attributes of mycorrhizal Douglas-fir seedlings. In vitro fungal ethylene production was poorly correlated with Douglas-fir morphological responses, but positively correlated with root IAA content for all three conifer species. These results suggest a relationship exists between the production of auxin and ethylene by ectomycorrhizal fungi and changes in endogenous IAA content of roots that could affect growth responses of conifer seedlings.