Growth Promotion and Biocontrol of Damping-Off of Pinus yunnanensis Seedlings by the Ectomycorrhizal Fungus Scleroderma citrinum Through Suppressing Two Local Soil Pathogens

Abstract

Several studies have confirmed that ectomycorrhizae could supply host plants nutrients and improve plant resistance against damping-off disease, which in turn promote plant growth and seedling survival rate. However, how the ectomycorrhizal fungi affect soil-borne pathogens were less known. Pinus yunnanensis (Yunnan pine) is a widely planted conifer species and is used for soil and water conservation in subtropical southwest China. Due to its strong reliance on ectomycorrhizae and low survival rate from damping-off in forest nurseries, we aimed to explore the ectomycorrhizal fungus Scleroderma citrinum for biological control of damping-off of P. yunnanensis seedlings caused by Fusarium solani and Rhizoctonia solani. In this study, we conducted five experiments to test the hypothesis that ectomycorrhizal fungus S. citrinum might inhibit damping-off disease caused by soilborne pathogens and promote host plant growth. Results showed that S. citrinum significantly suppressed the growth and pathogenic activity of both pathogens under Petri dish culture and sand culture directly (experiments 1, 2 and 3). Subsequently, a pathogen inoculation experiment under greenhouse condition showed that pathogenic activity of both F. solani and R. solani was lower in the treatment of both mycorrhizal seedlings and mycorrhizal soil (experiment 4). Finally, results from field soil tests showed that mortality and damping-off rate of P. yunnanensis seedlings significantly reduced in mycorrhizal soils collected from the field than that of control, suggesting that the suppression of pathogens also occurred in the field with mycorrhizal soil (experiment 5). We found a significant increase in seedling height, fresh weight and dry weight of the extract-treated or pre-inoculation of seedlings compared to the control. Furthermore, the protective effects of S. citrinum against damping-off by soil-borne pathogens and promoting plant-growth parameters were highly correlated to the colonization rate in the roots of P. yunnanensis seedlings. Based on the present experimental results we suggest that S. citrinum might have in vitro effective antagonistic activities against soil-borne fungi, and the greatest in vivo pathogen inhibitory capacities on damping-off disease and plant-growth promoting activities of P. yunnanensis seedlings. This would contribute to the biological control of ectomycorrhizal fungus S. citrinum defensed damping-off disease in forest nurseries of P. yunnanensis.

Keywords: Seedling nursery, Growth simulation, Biocontrol, Plant Protection, Mycorrhization