Cost of inoculating seedlings with Pisolithus tinctorius spores

Although the production of commercial products of vegetative Pt (Pisolithus tinctorius (Pers.) Coker & Couch) inoculums has ceased in North America due to a lack of demand by consumers, the number of products that contain Pt spores has increased.  The quality, quantity and price of these products vary considerably.  The cost of inoculating 1,000 tree seedlings with Pt basidiospores can vary from $0.45 to more than $30.  The cost of treating with Pt spores is lowest when seedlings are inoculated in a container nursery using rates that are less than 0.4 mg per seedling.  However, with some products the cost to treat 1,000 bareroot seedlings is greater than $500 when spores are applied in the planting hole.  Three decades ago, 1 g of Pt spores could be purchased for $0.13 and now the price of 1 g can exceed $14. Although many research papers provide data on the biological response to inoculating seedlings with spores, few document the cost of inoculation. Commercial products that are marketed toward homeowners containing both ectomycorrhizal and endomycorrhizal spores are more expensive than products that contain only ectomycorrhizal spores.  In situations where survival and growth of seedlings are not increased, the benefit/cost ratio will typically be less than one.