Endophytic fungi in the invasive weed Impatiens glandulifera: a barrier to classical biological control?

Abstract

SummaryThe 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.

Evaluation of foliar fungus‐mediated interactions with below and aboveground enemies of the invasive plant Ageratina adenophora

“…Many studies have verified that foliar fungi can help invasive host plants resist pathogens; for example, Currie et al. (2019) demonstrated that fungal endophytes appeared to be antagonistic to rust fungus ( Puccinia komarovii ). In this study, we found that the foliar fungus Colletotrichum sp.…”

“…might be a latent pathogen, and it enhanced the pathogenicity of D. helianthi on A. adenophora leaves; this fungus also marginally reduced the signs of herbivory on seedlings from natural insect enemies in the wild. Previously, invasive hosts have been shown to benefit from the presence of foliar fungi (Aschehoug et al., 2012; Currie et al., 2019; Evans, 2008; Xiao et al., 2012). The adverse impacts in this study may be related to the latent pathogenic effects of this foliar fungus but also reflect the fact that the ecological functions of foliar fungi are usually context dependent (Hawkes & Connor, 2017).…”

“…might be a latent pathogen, and it enhanced the pathogenicity of D. helianthi on A. adenophora leaves; this fungus also marginally reduced the signs of herbivory on seedlings from natural insect enemies in the wild. Previously, invasive hosts have been shown to benefit from the presence of foliar fungi (Aschehoug et al, 2012;Currie et al, 2019;Evans, 2008;Xiao et al, 2012).…”

“…For example, Aschehoug et al (2012) indicated that the inoculation of endophytic Alternaria (CID120) on the invasive forb Centaurea stoebe could directly increase its growth. Currie et al (2019) demonstrated that foliar fungi (Colletotrichum acutatum, Alternaria alternata and Cladosporium oxysporum) appeared to mitigate the effect of the pathogen Puccinia komarovii on the invasive weed Impatiens glandulifera. Rudgers and Clay (2008) showed that the foliar fungus Neotyphodium coenophialum could significantly reduce the abundance and diversity of herbivorous arthropods on the invasive plant Lolium arundinaceum.…”

The Potensial of Fusarium sp. and Chaetomium sp. as Biological Control Agents of Five Broad-Leaf Weeds

“…Weed biocontrol, especially by using plant pathogenic fungi, has recently received serious attention from the researchers in developed countries, because it has minimum negative side effects on the environment (Currie et al, 2020). Weed biological control is advantageous because it is environmentally friendly, reduces the use of pesticides, decreases environmental contamination, avoids health risks for farmers, is permanent, saves energy, does not pollute and is inexpensive compared to other methods and is sustainable (Harding and Raizada, 2015).…”