Endomycorrhizae and growth of 'Sweetheart' strawberry seedlings

Growth of strawberry (Fragaria xananassa Duch. 'Sweetheart') seedlings inoculated with six spore levels ranging from 0 to 12,000 spores/plant of the mycorrhizal fungi Glomus intraradices Schenck and Smith was studied in the greenhouse and with greenhouse plants subsequently moved to the field. Plant height, leaf area, and number of leaves increased significantly with inoculum spore densities ranging from 750 to 12,000 spores/plant in relation to control plants in the greenhouse and field. In the greenhouse, there was a linear relationship between percent infection and spore density, although the relationship was cubic in the field. In the field study, control plants were infected with indigenous mycorrhizae, but inoculated plants produced more runners than the control plants, and foliar Cu and Ca increased linearly with increased spore density. Inoculated plants contained significantly more dry matter than the controls. For inoculated plants, root dry weight increased linearly with increased spore density. We conclude that a minimum spore density of 750 spores/plant is sufficient for a positive growth response.