Waterlogging reduces soil colonization by antagonistic fungi and restores production in Ganoderma lucidum continuous cultivation

Ganoderma lucidum (GL) is an important traditional medicinal mushroom with a high economic value. Recently, Chinese GL farmers confronted a cultivation obstacle, wherein GL does not develop fruiting bodies on wood logs after being repeatedly transferred into cultivated soil. Soil surface colonization of non-GL fungi was observed and supposed to cause GL cultivation problems. Thus, a survey was carried out and the fungal colonies on the soil surface were recorded in a GL cultivation house in 2015 while a total of 346 fungal isolates were obtained. Based on phylogenetic analyses, most of these fungi were categorized into two genera, Trichoderma and Mucor. Both genera showed antagonistic activity against GL in vitro. Two trials, one in Lanju and the other in Chengbei, were conducted to follow the colonization trend of the soil surface by Trichoderma and Mucor. The number of colonies of both Trichoderma and Mucor increased dramatically during GL cultivation, with an increase of 15.4-fold and 13.4-fold in the Lanju trial in 2017 and 2018, respectively. Similar results occurred in the Chengbei trial. Organic matter in cultivation soil increased from 21.5 g kg(-1) to 129.7 g kg(-1) and from 20.9 g kg(-1) to 138.7 g kg(-1) in the Lanju and Chengbei trials, whereas total nitrogen increased from 0.8 g kg(-1) to 13.4 g kg(-1) and from 0.9 g kg(-1) to 14.9 g kg(-1), respectively. Sanitation management to reduce non-GL fungal colonies using waterlogging significantly reduced the number of colonies of Trichoderma and Mucor on soil surfaces. The percentage of developed fruiting bodies of GL in sanitized soil was about 90% and significantly higher than that of the control. Moreover, the spore yield of about 5 kg per house was produced from GL in sanitized soil while that failed in the control soil. In summary, the accumulation of the antagonistic Trichoderma and Mucor potentially caused by high nutrition levels contributed to the cultivation problems for GL. A practicable and effective sanitation method was proposed to manage this problem of GL production.