Dark Septate Endophytes Support Komatsuna Growth Under High Temperature Stress and Greenhouse Farming

Komatsuna (<i>Brassica rapa</i> var. <i>perviridis</i>) is one of the most common leafy vegetables in Japan. In recent years, the frequent occurrence of abnormally high temperatures is becoming a threat for komatsuna as it is vulnerable to high temperature stress. In natural ecosystems, most plants coexist with endophytic fungi as a strategy to adapt to stressful environments. Among known symbiotic fungi, there are dark septate endophytes (DSEs), which are unique due to their prevalence under stressed environmental conditions. This study aimed to evaluate the use of DSEs to improve komatsuna growth using a greenhouse farming system, as a practice to improve sustainable agriculture. We examined the effect of inoculation with three DSE isolates: <i>Phialocephala fortinii</i> KS.F.6 (Pf), <i>Exophiala pisciphila</i> KS.F.3.4 (Ep) and <i>Veronaeopsis simplex</i> Y34 (Vs), on the growth of komatsuna under high temperature stress. The preliminary experiment showed that inoculation with isolates Ep and Vs reduced the heat injury index and increased the number of surviving plants under 35 °C heat stress. Furthermore, the greenhouse experiment showed that Ep and Vs increase the number of leaves, fresh weight, and dry weight of komatsuna. This is considered the first report of DSE symbiosis potential for komatsuna high-temperature-stress mitigation and growth performance induction.