Several studies have demonstrated asymbiotic growth and development of arbuscular mycorrhizal (AM) fungi, although AM fungi are regarded as obligately symbiotic root-inhabiting fungi. Phytohormones, root exudates, and volatiles are important factors regulating the host-AM fungi interaction. However, the effects of phytohormones, root exudates, and volatiles on asymbiotic (without roots present) or pre-symbiotic (with roots present but no colonization) sporulation of AM fungi are unexplored. In this study, we tested the asymbiotic sporulation of Rhizophagus irregularis DAOM 197198 and further investigated the influences of abscisic acid (ABA), the exudates, and volatiles of tomato hairy roots on asymbiotic or pre-symbiotic sporulation in vitro. Results indicated that mother spores asymbiotically and pre-symbiotically produced daughter spores singly or in pairs. Compared with symbiotically produced spores, pre-symbiotically produced spores were significantly smaller (43.1 μm vs. 89.2 μm in diameter). Exogenous ABA applied to mother spores significantly increased the number of daughter spores, and root volatiles also significantly promoted pre-symbiotic sporulation. Our results provide the first evidence that exogenous ABA can promote AM fungal asymbiotic and pre-symbiotic sporulation, which highlights the potential role of phytohormones in AM fungal propagation.

中文翻译：

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外源脱落酸和根挥发物在非共生和共生前状态下增加不规则根瘤菌DAOM 197198的孢子形成。

尽管AM真菌被认为是专性共生生根真菌，但一些研究表明丛生菌根（AM）真菌的非共生生长和发育。植物激素，根系分泌物和挥发物是调节宿主-AM真菌相互作用的重要因素。但是，尚未研究植物激素，根系分泌物和挥发物对AM真菌的非共生性（无根）或共生前（有根但无定植）孢子形成的影响。在这项研究中，我们测试了不规则根瘤菌的非共生孢子形成DAOM 197198，并进一步研究了脱落酸（ABA），番茄毛状根的分泌物和挥发物对体外非共生或共生前孢子形成的影响。结果表明，母孢子非共生和共生前单独或成对产生子孢子。与共生产生的孢子相比，共生产生的孢子明显更小（直径为43.1μm，而直径为89.2μm）。外源ABA应用于母体孢子显着增加了子孢子的数量，并且根挥发物也显着促进了共生前的孢子形成。我们的结果提供了第一个证据，即外源ABA可以促进AM真菌的非共生和共生前孢子形成，这突出了植物激素在AM真菌繁殖中的潜在作用。