A plant production system called Veggie was launched to the International Space Station (ISS) in 2014. In late 2015, during the growth of Zinnia hybrida cv. ‘Profusion’ in the Veggie hardware, plants developed chlorosis, leaf curling, fungal growth that damaged leaves and stems, and eventually necrosis. The development of symptoms was correlated to reduced air flow leading to a significant buildup of water enveloping the leaves and stems in microgravity. Symptomatic tissues were returned to Earth on 18 May 2016 and were immediately processed to determine the primary causal agent of the disease. The presumptive pathogen was identified as Fusarium oxysporum by morphological features of microconidia and conidiophores on symptomatic tissues; that is, by epifluorescent microscopy (EFM), scanning electron microscopy (SEM), metabolic microarrays, and ITS sequencing. Both EFM and SEM imaging of infected tissues showed that germinating conidia were capable of stomatal penetration and thus acted as the primary method for infecting host tissues. A series of ground-based pathogenicity assays were conducted with healthy Z. hybrida plants that were exposed to reduced-airflow and high-water stress (i.e., encased in sealed bags) or were kept in an unstressed configuration. Koch's postulates were successfully completed with Z. hybrida plants in the lab, but symptoms only matched ISS-flown symptomatic tissues when the plants were stressed with high-water exposure. Unstressed plants grown under similar lab conditions failed to develop the symptoms observed with plants on board the ISS. The overall results of the pathogenicity tests imply that F. oxysporum acted as an opportunistic pathogen on severely high-water stressed plants. The source of the opportunistic pathogen is not known, but virulent strains of F. oxysporum were not recovered from unused materials in the Veggie plant pillow growth units assayed after the flight.

中文翻译：

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尖孢镰刀菌作为在国际空间站上生长的百日草植物上的机会性真菌病原体

一个名为 Veggie 的植物生产系统于 2014 年发射到国际空间站 (ISS)。2015 年底，在Zinnia hybrida cv. 的生长过程中。Veggie 硬件中的“大量”植物出现萎黄病、卷叶、真菌生长，损害叶和茎，并最终坏死。症状的发展与气流减少相关，导致微重力下大量水包裹叶和茎。有症状的组织于 2016 年 5 月 18 日返回地球，并立即进行处理以确定该疾病的主要病原体。推测的病原体被确定为尖孢镰刀菌通过症状组织上的小分生孢子和分生孢子的形态特征；也就是说，通过落射荧光显微镜 (EFM)、扫描电子显微镜 (SEM)、代谢微阵列和 ITS 测序。受感染组织的 EFM 和 SEM 成像均显示萌发的分生孢子能够穿透气孔，因此是感染宿主组织的主要方法。对暴露于气流减少和高水分胁迫（即装在密封袋中）或保持在无压力配置中的健康Z. hybrida植物进行了一系列基于地面的致病性测定。用Z. hybrida成功完成了 Koch 的假设实验室中的植物，但是当植物受到高水暴露的压力时，症状仅与国际空间站飞行的症状组织相匹配。在类似实验室条件下生长的无压力植物未能出现在国际空间站上观察到的症状。致病性测试的总体结果表明尖孢镰刀菌在严重高水胁迫的植物上是一种机会性病原体。机会性病原体的来源尚不清楚，但在飞行后测定的 Veggie 植物枕头生长单元中未从未使用的材料中回收到尖孢镰刀菌的毒株。