Extracellular Self-DNA Accumulation as a Potential Driver of Continuous Cropping Obstacle in Morchella sextelata and Morchella eximia

Continuous cropping obstacle (CCO) is becoming a major restrictive factor limiting the sustainable development of morel industry. The species-specific autotoxicity of extracellular self-DNA (esDNA) may be one of the primary drivers underlying the occurrence of CCO. In this study, the effects of short fragments (≤250 bp) of esDNA or extracellular DNA (exDNA) on mycelial growth of cultivable Morchella eximia and M. sextelata were assayed. These effects were quantified using a response index (RI). The results indicated the dose-dependent, strain-specific, and conspecific autotoxicity of esDNA in cultivable morels. At ecologically relevant DNA concentrations, the strain-specific and conspecific growth inhibitory effects of esDNA in tested Morchella strains were consistently negative (RI < 0). Additionally, our study found that the growth-inhibitory effects of exDNA from M. sextelata on M. eximia strains were weaker than those observed in the reverse scenario. Taken together, our study suggests, for the first time, the conspecific autotoxicity of esDNA in cultivable Morchella under laboratory conditions, providing novel insights into the potential mechanisms of CCO and highlighting its prospective applications in morel production.