Amino Acid-Optimized Medium Improves Long-Term Growth, Conidiation, Stress Tolerance, and Biocontrol Performance of Esteya vermicola Against Pinewood Nematode

<i>Esteya vermicola</i> is a nematophagous fungus with strong parasitic ability against the pinewood nematode (<i>Bursaphelenchus xylophilus</i>) and shows great potential for the biological control of pine wilt disease. However, this fungus is highly sensitive to environmental stress factors and often exhibits early necrosis when cultured on conventional nutrient-rich media, limiting its large-scale application. In this study, we optimized the long-term cultivation and conidiation conditions of <i>E. vermicola</i> CBS115803 by supplementing minimal medium (MM) with amino acids, and evaluated its stress tolerance and infectivity against the pinewood nematode. Among 20 tested amino acids, histidine significantly increased total conidia production, while arginine, glutamine, and proline markedly promoted the formation of lunate conidia. The combination of arginine, histidine, glutamine, and proline (AHGP) produced the highest overall conidia yield and lunate conidia proportion. The MM + AHGP medium maintained long-term colony viability, whereas colonies on PDA and CM media showed obvious degeneration. This formulation also improved mycelial growth, total conidiation, and the proportion of lunate conidia. Moreover, conidia produced on MM + AHGP exhibited the highest germination rates and infectivity under various stress conditions, including cold, heat, oxidative, osmotic, and UV stresses. Conidia germination was significantly enhanced following treatment at 0 °C, suggesting that low temperatures may activate dormancy-breaking pathways. This amino acid-optimized medium offers an effective technical foundation for stable large-scale production and storage of <i>E. vermicola</i> conidia, providing a new avenue for the biocontrol of pine wilt disease.