Performance of Pinus contorta inoculated with two strains of root endophytic fungus, Phialocephala fortinii: effects of synthesis system and glucose concentration

Abstract

Melanized, root-colonizing fungi are ubiquitous. Their ecological role, however, is poorly understood, and results of studies of associations between these fungi and their potential host plants are controversial. The culture system under which the association is studied may also affect the host-fungus interaction. Two experiments on the association between Pinus contorta Dougl. ex Loud., and a root-inhabiting endophytic fungus, Phialocephala fortinii Wang & Wilcox, were conducted to study the host response to inoculation. First, Pinus contorta seedlings were inoculated with two strains of Phialocephala fortinii and grown under aseptic conditions with five levels of glucose in the medium. Multiple linear regression analysis was employed to study the effects of inoculation and glucose concentration. Second, the same two strains of Phialocephala fortinii were inoculated on Pinus contorta seedlings in open pot cultures. Inoculation resulted in substantial increase in all biomass components of the host plant in the aseptic culture system. Total biomass, for example, was increased approximately 60 and 90% when seedlings were inoculated with strain 1 and strain 2, respectively. No seedling mortality was observed following fungal inoculation after 6 months of incubation. Inoculation increased host biomass with increasing glucose concentration, while glucose concentration did not significantly affect host biomass when no inoculum was added. Inoculation lowered foliar nitrogen and phosphorus concentrations. The effect of glucose concentration on the foliar nutrient concentrations varied between the two strains. In the open pot cultures, inoculation did not affect biomass or foliar nutrient concentration. We hypothesise that the observed increases in host growth in the aseptic culture system are due to fungal respiration in a closed culture system, the carbohydrates made available to the host plant by the fungus, or, most likely, to a combination of both factors. The ecological role of Phialocephala fortinii and the validity of aseptic culture assays are discussed.Key words: dark-septate endophytes, deuteromycetes, fungi, host-fungus associations, root endophytes, symbiosis.