Improved Rhizopogon Mycorrhizal Colonization and Foliar Nutrient Levels in Ponderosa Pine and Douglas-Fir with Myconate(r)

Abstract

The importance of mycorrhizal colonization in the establishment and growth of forest trees has long been recognized, and mycorrhizal inoculum is used regularly in replanting. The isoflavonoid formononetin (7-hydroxy-4′-methoxy isoflavone), sold as Myconate(r), has been shown to increase colonization by endo- but not ectomycorrhizae. The purpose of this study was to test the ability of Myconate(r) to increase colonization, nutrient uptake, and growth in ponderosa pine and Douglas-fir seedlings inoculated with Rhizopogon ectomycorrhizae spores. In these tests Myconate(r) significantly increased root colonization by Rhizopogon in both tree species at 60 mg/L. In Douglas-fir seedlings, potassium content was significantly higher in seedlings treated with 60 mg/L of Myconate(r) and Rhizopogon parksii than in either the untreated plants, or those treated with R. parksii alone. Treatment with R. parksii and Myconate(r) significantly increased Douglas-fir phosphorus and nitrogen content over the untreated control, but not over the treatment with R. parksii alone. In ponderosa pine seedlings, Myconate(r) treatment at 60 mg/L significantly increased nitrogen, but not phosphorus or potassium content over seedlings treated with R. rubescens alone. Caliper diameter of ponderosa pine was not significantly increased with the application of Myconate(r), while in Douglas-fir, both R. parksii and R. parksii plus Myconate(r) treatments increased caliper size over the control.