Herbaceous plants harbour species-rich communities of asymptomatic endophytic fungi. Although some of these endophytes are entomopathogenic, many are not, and remarkably little is known about how the ...presence of these fungi in plant tissues affects phytophagous insects.
Here we show through a meta-analysis that both entomopathogenic and nonentomopathogenic endophytes have a negative effect on insect herbivores. Growth and performance of polyphagous and sucking insects are reduced by nonentomopathogenic endophytes, but monophages are unaffected, likely because the latter are better adapted to secondary metabolites produced or induced by the fungi.
Furthermore, studies using excised leaves report weaker effects than those with intact plants, likely caused by chemical changes being masked by leaf excision. Most surprisingly, endophyte infection of seeds produces the greatest effect on insect herbivores in subsequent mature plants, even though the usual mode of fungal transmission is infection of leaves by air-borne spores.
We conclude that these ubiquitous hidden fungi may be important bodyguards of plants. However, in order to fully understand their roles in plant protection, we must be aware that minor differences in experimental design can lead to contradictory results.
Himalayan balsam (Impatiens glandulifera) is one of the most invasive weeds across Europe. The rust fungus, Puccinia komarovii var. glanduliferae has been introduced as a biological control agent, ...but success has been patchy. Here, we investigated whether mycorrhizal and endophytic fungi can affect rust efficacy and plant growth. Over three experiments, we found that AM fungi and the rust alone or together consistently reduced plant growth, but this depended on the identity of species in the AM inoculum. Meanwhile, AM fungi increased infection frequency of the endophyte Colletotrichum acutatum. Rust inoculation had no detrimental effects on mycorrhizal colonisation or C. acutatum infection, but the latter two fungi reduced rust sporulation. However, plant size was reduced when all three fungal types were present, suggesting that a combined fungal inoculum offers a promising approach for the control of this weed.
The annual plant Impatiens glandulifera (Himalayan balsam) is the most widespread invasive non‐native weed in the British Isles. Manual control is widely used, but is costly and laborious. Recently, ...biological control using the rust fungus Puccinia komarovii var. glanduliferae has been trialled. We designed an experiment to assess the impact of these control methods on invertebrate communities in relation to unmanaged and uninvaded habitats, and to determine whether mycorrhizal inoculation aided post‐control recovery of these communities. Sixty invaded and twenty uninvaded field soil blocks were transplanted to the experiment site, where a mycorrhizal inoculum was added to half of all blocks. Biological and mechanical control treatments were applied to twenty invaded blocks independently; the twenty remaining invaded blocks were left intact. Above‐ and belowground invertebrate samples were collected from the blocks at the end of the growing season. Overall, aboveground invertebrate abundance increased with the removal of I. glandulifera, and several groups showed signs of recovery within one growing season. The effect of mechanical control was more variable in belowground invertebrates. Biological control did not affect aboveground invertebrate abundance but resulted in large increases in populations of belowground Collembola. Our experiment demonstrates that mechanical removal of I. glandulifera can cause rapid increases in invertebrate abundance and that its biological control with P. komarovii var. glanduliferae also has the potential to benefit native invertebrate communities.
1 Endophyte fungi exist within the living tissues of all plants, but compared with grasses and trees, remarkably little is known about their ecology in herbaceous species. These fungi produce an ...array of metabolites in culture and there is some evidence that they can increase the resistance of plants to herbivorous insects. 2 As herbaceous plant endophytes are thought to be unspecialized, ubiquitous taxa, we hypothesized that their occurrence within two closely related plant species would not vary between local plant communities. Furthermore, we expected to find negative relations between endophyte occurrence and that of a herbivorous insect. 3 We tested these hypotheses by isolating endophytes from Leucanthemum vulgare and Cirsium arvense (Asteraceae) plants growing together in five populations, each about 13 km apart. Damage by the leaf mining fly, Chromatomyia syngenesiae, was also measured on each plant. 4 C. arvense harboured more species of fungi per plant and the number of isolates recovered per leaf was also higher. Several fungi showed differences in occurrence within the two plants, but these differences were not consistent between sites. The similarity in the endophyte assemblage decreased with increasing intersite distance in C. arvense, but not in L. vulgare. We conclude that endophytes either colonize C. arvense more readily or have greater activity within this host (or both). 5 Leaf miner attack was positively related to total endophyte species number in L. vulgare, but not so in C. arvense, while occurrence of Chaetomium species was negatively associated with insect attack in both plants. In L. vulgare, only 5% of relations between occurrence of different endophyte species were significant, but in C. arvense this figure was 43% and all were negative. 6 This study has important implications for understanding the factors that influence plant resistance to insects. It is the first report of endophytic fungi affecting host plant choice by insects in herbaceous plants. The abundance of unspecialized endophytes in forbs means that they are a neglected, but important, aspect of plant-herbivore relations.
▶ Arbuscular mycorrhizas enable a plant to tolerate root herbivory. ▶ Root feeding increases arbuscule counts in clover roots. ▶ Two mycorrhizal species are better than one in defending a plant. ▶ A ...specialist root feeder is positively affected by mycorrhizas.
Arbuscular mycorrhizal fungi (AMF) are known to reduce the growth of generalist root-feeding insects, but whether the same is true for a specialist insect is unknown.
White clover (
Trifolium repens) was inoculated with the AM fungi
Glomus fasciculatum and
Glomus mosseae individually and in combination, and larvae of the clover root weevil (
Sitona lepidus) reared on mycorrhizal and non-mycorrhizal plants. On emergence, adult weevils were weighed and the percentage of larvae surviving to adulthood was calculated for each treatment.
Larval survival to adulthood was increased by both species of fungi, but weight was unaffected. Larval feeding reduced foliar biomass, but had no effect when two fungi colonized the root system. Although larval survival was greatest in the dual fungal treatment, the proportion of grazed root nodules was lower, suggesting that AMF may improve root quality for the herbivore. Root feeding caused an increase in arbuscular colonization in the dual fungal treatment, and this may have enabled plants to tolerate herbivory, through enhanced mycorrhizal benefit.
We conclude that a specialist root feeder is less affected by the presence of AMF than are generalist species. However, AMF enable a plant to tolerate the effects of root loss, and this is dependent on the number of mycorrhizal species in the root system.
The objective of this study was to determine if root-feeding by insect larvae affects subsequent colonization of roots by arbuscular mycorrhizal fungi. We investigated grazing by larvae of
Tipula ...paludosa on colonization of
Agrostis capillaris by two species of fungi,
Glomus mosseae and
G. intraradices. Host plants were subjected to 7 days of grazing only, continuous grazing for 42 days, or no herbivory. Those plants with no herbivory had significantly lower levels of colonization by arbuscules and hyphae compared to plants which were grazed for 7 or 42 days. The effect only occurred in the upper parts of the root system, where larvae were active. We suggest that this effect was most likely mediated by a change in quantity and composition of root exudates.
All vascular plants contain communities of endophyte fungi within their foliar tissues. These fungi can act as plant bodyguards and disrupt the efficacy of weed biological control agents, yet studies ...of invasive plant biology hardly ever consider the background endophyte communities. Here, we investigated the factors that affect the structure of cultivable endophyte communities in the highly invasive weed Impatiens glandulifera. We found that community composition varies according to location, but that seasonal accumulation patterns of endophytes are similar between sites. Biotic factors influencing endophytes include arbuscular mycorrhizal fungi, insect herbivores and plant pathogens. Endophyte species richness per plant was consistently low compared with other herbaceous plants and communities appear to be a random sub-set of the available species pool, with the plant acting as a strong filter of species. This information should enable community structure to be modelled and manipulated, making biological control of this weed more effective.
The linkages between plants and soil biota are both important and complex, involving both positive and negative feedbacks between soil organisms and their physical environment. An experiment was ...established in an upland grassland system to investigate the impact of addition of nitrogen and lime (NL) fertiliser on plant communities and the soil biota. The NL treatment increased above ground plant biomass and accelerated root returns to the soil, providing increased plant-derived energy for the soil food web. No changes were seen in fungal biomass, as indicated by PLFA, but bacterial biomass was reduced. However, the numbers of bacterial feeding and predatory nematodes increased in the NL treatment and may be masking the effects at the lower trophic levels, indicating top-down control mechanisms. Although the NL treatment changed nematode community structure, there was an overall depression in the abundance of nematodes. This decrease was likely to be related to soil moisture content, which was reduced significantly in the NL treatment by increased evapotranspiration due to the larger above ground biomass production. This study highlights the strong bottom-up control over the soil dwelling nematodes both in terms of driving changes in diversity and in modifying the soil physical environment.
Fatty acids are essential to most organisms and are made endogenously by the fatty acid synthase (FAS). FAS is an attractive target for antibiotics and many inhibitors are in clinical development. ...However, some gram-negative bacteria harbor an enzyme known as the acyl-acyl carrier protein synthetase (AasS), which allows them to scavenge fatty acids from the environment and shuttle them into FAS and ultimately lipids. The ability of AasS to recycle fatty acids may help pathogenic gram-negative bacteria circumvent FAS inhibition. We therefore set out to design and synthesize an inhibitor of AasS and test its effectiveness on an AasS enzyme from Vibrio harveyi, the most well studied AasS to date, and from Vibrio cholerae, a pathogenic model. The inhibitor C10-AMS 5'-O-(N-decanylsulfamoyl)adenosine, which mimics the tightly bound acyl-AMP reaction intermediate, was able to effectively inhibit AasS catalytic activity in vitro. Additionally, C10-AMS stopped the ability of Vibrio cholerae to recycle fatty acids from media and survive when its endogenous FAS was inhibited with cerulenin. C10-AMS can be used to study fatty acid recycling in other bacteria as more AasS enzymes continue to be annotated and provides a platform for potential antibiotic development.
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