Effects of <i>Isaria cateniannulata</i> on the colonization process and enzyme activity of <i>Fagopyrum tataricum</i> seeds during germination

Endophytic colonization of entomopathogenic fungi has garnered significant attention for its role in promoting plant growth. Specifically, <i>Isaria cateniannulata</i> has shown a positive effect on the germination of <i>Fagopyrum tataricum</i> (buckwheat) seeds, but the mechanisms underlying this promotion remain unclear. This study aims to elucidate the colonization process of <i>I. cateniannulata</i> in <i>F. tataricum</i> seeds during germination stages, quantify the colonization efficiency and tissue specificity of the fungus, and investigate the temporal dynamics of antioxidant enzyme activities and malondialdehyde content triggered by fungal colonization. Furthermore, we evaluated the potential of <i>I. cateniannulata</i>-colonized seedlings to suppress <i>T. urticae</i> populations through oviposition inhibition. The results demonstrated for the first time that <i>I. cateniannulata</i> could successfully colonize germinating <i>F. tataricum</i> seeds during the seed imbibition and germination stages, either by forming dissolution zones with its spores or by germinating and forming mycelia. Initial colonization of all tissues was observed within 16 h, with colonization rates peaking after 5 d, with a preferential colonization rate observed as endosperm > embryo > seed coat. Furthermore, the colonization by <i>I. cateniannulata</i> enhanced peroxidase (POD) activity in the embryo and reduced malondialdehyde (MDA) content. Seedlings grown after colonization were also found to effectively reduce the number of eggs laid by <i>T. urticae</i>. These findings provide both theoretical insights and practical foundations for developing a symbiotic system between <i>I. cateniannulata</i> and <i>F. tataricum</i> seeds.