福廷瓶头霉与马尾松的共生特征

深色有隔内生真菌（dark septate endophyte,DSE）广泛定殖于植物根系,对促进植物生长、提高植物抗逆能力具重要作用。本研究从马尾松Pinus massoniana根系分离到一株DSE,于无菌条件下研究了此菌与马尾松的共生特征,研究结果表明：基于形态学和分子生物学分析,此菌被鉴定为福廷瓶头霉Phialocephala fortinii,在PDA培养基25℃培养条件下,此菌不产孢,菌丝深色、具隔,最适培养基为PDA。此菌与马尾松根系共生体的形成过程可划分为3个时期,即侵入前期：接种后2d,新生菌丝向马尾松根系定向生长并开始接触根系,但未侵入根系内部;侵入期：接种后4d,菌丝与马尾松根系接触侵入根内并在根系皮层细胞间扩展延伸;形成期：接种后6d,菌丝继续在马尾松根系内扩展并形成富含脂类物质的微菌核。接种福廷瓶头霉显著增加了马尾松生物量的积累（P<0.05）,并影响了其根系发育。接种后,马尾松主根生长受限,侧根生长显著提高（P<0.05）,侧根长度较未接种处理增加了112.87%。被侵染根系的根毛数量减少,并由大量根外菌丝包裹。以上结果对进一步揭示DSE与宿主的共生机理有一定指导意义。

Characteristics of Phialocephala fortinii and Pinus massoniana symbiosis

Dark septate endophytes (DSE) are extensively inhabiting roots of a wide range of plants and play vital roles in promoting plant growth and improving plant performance under various adverse environments. In this study, a DSE strain was isolated from Pinus massoniana root and its symbiotic characteristics with P. massoniana were investigated under aseptic conditions. Morphological and molecular biological evidence indicated that the DSE isolated was Phialocephala fortinii. Under pure culture condition, P. fortinii does not produce spores, and its septate mycelium is melanized with septa. PDA medium is most suitable for its growth. Three periods emerged during the symbiosis establishment between P. fortinii and P. massoniana. In the pre-infection phase, the newly emerged hyphae grew towards and started attaching the root in 2 days of post inoculation (dpi), but without hyphal penetration. During the infection phase, the mycelium began penetrating into the root of P. massoniana, and the intraradical mycelium extended radially along the intercellular space of cortical cells in 4 dpi; in 6 days of post-inoculation, the mycelium continued to expand in the roots and formed intensive microsclerotia filled with lipids. P. fortinii inoculation significantly increased the biomass of P. massoniana (P<0.05) and modified root development. The growth of the primary root was hampered, while the growth of the lateral root significantly increased (P<0.05). The length of the lateral root increased by 112.87% as compared with the non-inoculation treatment. Root hairs in the infected roots were bound by intensive extraradical mycelium. The results provide reference for further investigation of the symbiotic mechanisms between DSE and its host.