Do concentrations of glucose and fungal inoculum influence the competitiveness of two early-stage ectomycorrhizal fungi in Afzelia africana seedlings?

Abstract

This study was conducted to compare the growth and the competitiveness of two early-stage fungi, Thelephoroid fungal species ORS.XM002 and Scleroderma dictyosporum Pat. 7731, on Afzelia africana seedlings, at different concentrations of glucose and fungal inoculum. Thelephoroid fungal sp. grew better continuously across agar in glucose concentrations at 0.0 and 0.1 g/l, whereas S. dictyosporum required the highest concentrations of glucose at 1.0 and 10.0 g/l to sustain growth. When both fungi were inoculated together in an axenic condition, Thelephoroid fungal sp. colonized better Afzelia seedlings than S. dictyosporum, whatever the concentrations of glucose. When both fungi were inoculated together in an ECM propagule-free savanna soil at different concentrations of fungal inoculum, they appeared in sequence, which permitted distinction between Thelephoroid fungal sp. that occurred first in the colonization process, and S. dictyosporum that occurred later. At 6 months, Thelephoroid fungal sp. alone or together with S. dictyosporum colonized from 45 to 60% of lateral roots in A. africana seedlings, while the ectomycorrhizal colonization by S. dictyosporum together with Thelephoroid fungal sp. did not exceed 10%. Moreover, seedlings inoculated by Thelephoroid fungal sp. alone or in combination with S. dictyosporum grew better than those of S. dictyosporum alone or controls in terms of height and root dry weight. These results suggest that Thelephoroid fungal sp. has a lower requirement for glucose than S. dictyosporum. This may be advantageous to Thelephoroid fungal sp. in colonizing Afzelia roots more quickly than S. dictyosporum. However, results did not support the hypothesis that the initial ectomycorrhizal colonization was related to the density of fungal propagules in the soil, as indicated elsewhere.