Identification of allelochemicals under continuous cropping of Morchella mushrooms

Continuous cropping obstacle has been becoming the bottleneck for the stable development of morel cultivation. The allelopathic effect of soil allelochemicals may play an instrumental role in the morel soil sickness. In this study, the allelochemicals were identified by gas chromatography-mass spectrometry (GC-MS) combined with in vitro bioassay. A total of 61 chemical substances were identified through the GC-MS analysis of 12 replanting and control soil samples, comprising 10 phenolic acids, 36 acids, 3 aldehydes, etc. Among which, 15 compounds with values of variable importance for the projection (VIP) greater than 1 in the orthogonal partial least squares-discriminant analysis (OPLS-DA) were selected as the differential metabolites between soil samples of continuous cropping and control. The bioassay showed that 4-coumaric acid and vanillic acid exhibited inhibitory effect on mycelial growth of three cultivated Morchella mushrooms (M. sextelata, M. eximia and M. importuna) under soil native concentrations. Analysis of potential biosynthetic pathways of phenolic acids found that the 3 cultivable Morchella mushrooms are unable to synthesize phenolic acid allelochemicals. Therefore, although they were detected in trace amounts in static culture broth of M. sextelata, the two phenolic acids can only be defined as morel allelochemicals rather than autotoxins. Taken together, we found two morel allelochemicals that may derive from morel related microbes and plants, which will be helpful for further fundamental study and application in morel artificial cultivation.