The rust fungus, Puccinia komarovii var. glanduliferae, has been introduced into the UK for biological control of the invasive weed, Impatiens glandulifera (Himalayan balsam). However, establishment of the pathogen has differed across the country, which may be partly explained by variation in plant genotype. The aim of this study was to examine whether there is a further layer of phenotypic resistance, provided by indigenous foliar endophytic fungi. Culturable endophytes were isolated from a number of different balsam populations, and the commonest species were inoculated into ‘clean’ balsam plants, to test their interactions with the rust. We found that endophyte communities within balsam are low in diversity and become more dissimilar with increasing distance between populations. Three endophytes (Colletotrichum acutatum, Alternaria alternata and Cladosporium oxysporum) were common and appeared to be antagonistic to the rust, reducing pustule number and mitigating the effect of the pathogen on plant biomass. I. glandulifera thus partially conforms to the endophyte‐enemy release hypothesis, in that as an introduced species, it has an impoverished endophyte complement, acquired from the local environment. However, these endophytes represent a potential barrier to effective biological control and future weed control strategies need to find strains of rust that can overcome plant genetic resistance and the overlaying phenotypic resistance, conferred by endophytes. Future classical biological control programmes of weeds must therefore take into account the fungal bodyguards that invasive species may acquire in their introduced ranges.

中文翻译：

---

入侵杂草Impatiens glandulifera中的内生真菌：经典生物学控制的障碍？

锈菌，Puccinia komarovii var。菊科，已被引入英国以对入侵杂草凤仙花进行生物控制（喜马拉雅香脂）。然而，病原体的建立在全国范围内有所不同，其部分原因可能是植物基因型的差异。这项研究的目的是检查是否存在由本土叶内生真菌提供的另一种表型抗性。从许多不同的苦瓜种群中分离出可培养的内生菌，然后将最常见的物种接种到“干净的”苦瓜植物中，以测试它们与铁锈的相互作用。我们发现苦瓜中的内生菌群落多样性较低，并且随着种群之间距离的增加而变得越来越不相似。3种内生真菌（炭疽菌，链格孢菌和氧化克孢菌））很常见，似乎对铁锈有拮抗作用，减少脓疱数量并减轻病原体对植物生物量的影响。因此，I。glandulifera部分符合内生菌-敌人释放假说，因为它是一种引入的物种，具有从当地环境中获取的贫化的内生菌补体。然而，这些内生菌代表了有效生物学控制的潜在障碍，未来的杂草控制策略需要找到能够克服植物内生菌赋予的植物遗传抗性和覆盖表型抗性的锈菌。因此，未来的经典杂草生物防治计划必须考虑到入侵物种在其引入范围内可能获得的真菌保镖。