Root colonization and growth response of Pinus nigra seedlings to three types of ectomycorrhizal inoculum

Native mycorrhizal fungal species can colonize the roots of tree seedlings and positively influence their growth and survival. This study evaluates the effects of three native ectomycorrhizal fungi on the growth and root colonization of black pine (Pinus nigra) seedlings from three distinct origins. For this purpose, the experiment included (i) the production of pure cultures of selected local mycorrhizal fungal species in the laboratory environment and (ii) the production of mycorrhizal black pine seedlings carried out by inoculating plants with these cultures. Pure cultures of three fungal species (Rhizopogon luteolus, Russula raoultii and Chroogomphus rutilus) were obtained from eastern Mediterranean black pine forests of Turkey and mixed into sterilized growth substrate (a mixture of humus, river sand and forest soil) for inoculation. Two other treatments, with no mycorrhizal inoculations, were also added to the experiments and considered as sterile and non-sterile control treatments. Twenty-two months after inoculation, seed origin significantly affected seedling growth parameters and survival rates. Among the tested provenances, Egirdir consistently exhibited the lowest growth performance. Mycorrhizal inoculation did not significantly influence shoot growth; however, it markedly enhanced survival rates, root length, and the extent of mycorrhizal root colonization. The mean mycorrhizal infection rate was 1.6% in the sterile control and 27% in the non-sterile control. In contrast, inoculation with pure cultures increased colonization to 61%, 64%, and 69% for R. raoultii, C. rutilus, and R. luteolus, respectively. Survival rates showed a significant interaction between origin and mycorrhizal inoculation. R. luteolus consistently resulted in the highest survival rates across all treatments, with the most pronounced effect observed in the Egirdir provenance, where survival increased from 63% to 81% following inoculation. The improved seedling survival of the Egirdir origin, which had the smallest seeds and weakest initial growth, suggests that the benefits of mycorrhizal symbiosis may be especially important for weaker seedlings and under unfavorable environmental conditions.