Variable effects of endophytic fungus on seedling establishment of fine fescues

The fungus Clonostachys epichloë alters the influence of the Epichloë endophyte on seed germination and the biomass of Puccinellia distans grass

The fungal grass endophyte Epichloë typhina (Pers.) Tul. & C. Tul. (Ascomycota: Clavicipitaceae) grows intercellulary in aerial plant parts and reproduces asexually by invading host seeds. In this phase, it enhances seed production and germination, which accelerates its vertical spread. This relationship may be distorted by other seed-born fungi, whose spread is not so directly dependent on the success of the grass. Recently, the fungus Clonostachys epichloë Schroers has been observed on Puccinellia distans (Jacq.) Parl seeds originating from grass clumps infested with stromata, sexual structures of Epichloë typhina that are formed in spring on some host culms, preventing flower and seed development ('choke disease'). C. epichloë shows mycoparasitic activity toward Epichloë stromata by reducing the production of ascospores, which are responsible for horizontal transmission of the fungus. The aim of this study was to investigate the effect of seed-borne C. epichloë on seed germination, as well as the size and weight of P. distans seedlings and to examine whether C. epichloë alters the influence of Epichloë in the early developmental stages of P. distans. The results showed that if C. epichloë acts on seeds together with E. typhina endophytes, the seeds were negatively affected due to the elimination of the positive effect of the latter in terms of both seed germination rate and seedling length. At the same time, C. epichloë increased the proportion of E. typhina-untreated germinated seeds. Additionally, only the joint action of the two fungi, E. typhina and C. epichloë, effectively stimulated seedling dry mass; the presence of E. typhina alone was not sufficient to noticeably affect seedling size. Based on the increasing commonality of C. epichloë on Epichloë stromata, as well as its potential to be used in biocontrol of 'choke disease', we should take a closer look at this fungus, not only in terms of its mycoparasitic ability, but also in terms of its cumulative impact on the whole Epichloë-grass system.

Local adaptation in fungi

In this review, I explore the pervasive but underappreciated role of local adaptation in fungi. It has been difficult historically to study local adaptation in fungi because of the limited understanding of fungal species and their traits, but new hope has been offered with technological advances in sequencing. The filamentous nature of fungi invalidates some assumptions made in evolution because of their ability to exist as multinucleate entities with genetically different nuclei sharing the same cytoplasm. Many insights on local adaptation have come from studying fungi, and much of the empirical evidence gathered about local adaptation in the context of host-pathogen interactions comes from studying fungal virulence genes, drug resistance, and environmental adaptation. Together, these insights paint a picture of the variety of processes involved in fungal local adaptation and their connections to the unusual cell biology of Fungi (multinucleate, filamentous habit), but there is much that remains unknown, with major gaps in our knowledge of fungal species, their phenotypes, and the ways by which they adapt to local conditions.

Plant performance response to eight different types of symbiosis

Almost all plant species interact with one or more symbioses somewhere within their distribution range. Bringing together plant trait data and growth responses to symbioses spanning 552 plant species, we provide for the first time on a large scale (597 studies) a quantitative synthesis on plant performance differences between eight major types of symbiosis, including mycorrhizas, N-fixing bacteria, fungal endophytes and ant-plant interactions. Frequency distributions of plant growth responses varied considerably between different types of symbiosis, in terms of both mean effect and 'risk', defined here as percentage of experiments reporting a negative effect of symbiosis on plants. Contrary to expectation, plant traits were poor predictors of growth response across and within all eight symbiotic associations. Our analysis showed no systematic additive effect when a host plant engaged in two functionally different symbioses. This synthesis suggests that plant species' ecological strategies have little effect in determining the influence of a symbiosis on host plant growth. Reliable quantification of differences in plant performance across symbioses will prove valuable for developing general hypotheses on how species become engaged in mutualisms without a guarantee of net returns.

Postglacial colonization history reflects in the genetic structure of natural populations of Festuca rubra in Europe

We conducted a large-scale population genetic survey of genetic diversity of the host grass Festuca rubra s.l., which fitness can be highly dependent on its symbiotic fungus Epichloë festucae, to evaluate genetic variation and population structure across the European range. The 27 studied populations have previously been found to differ in frequencies of occurrence of the symbiotic fungus E. festucae and ploidy levels. As predicted, we found decreased genetic diversity in previously glaciated areas in comparison with nonglaciated regions and discovered three major maternal genetic groups: southern, northeastern, and northwestern Europe. Interestingly, host populations from Greenland were genetically similar to those from the Faroe Islands and Iceland, suggesting gene flow also between those areas. The level of variation among populations within regions is evidently highly dependent on the postglacial colonization history, in particular on the number of independent long-distance seed colonization events. Yet, also anthropogenic effects may have affected the population structure in F. rubra. We did not observe higher fungal infection rates in grass populations with lower levels of genetic variability. In fact, the fungal infection rates of E. festucae in relation to genetic variability of the host populations varied widely among geographical areas, which indicate differences in population histories due to colonization events and possible costs of systemic fungi in harsh environmental conditions. We found that the plants of different ploidy levels are genetically closely related within geographic areas indicating independent formation of polyploids in different maternal lineages.

Investigating the Role of Endophytic Fungi in Gentiana scabra bge. by Cross-Growth Period Inoculation

Gentiana scabra Bge. (gentian) is a Chinese medicinal plant. Endophytic fungi from the roots of gentian were isolated and cross-growth period inoculation was performed to study the roles of three Trichoderma spp. strains (F1, F2, and F9) in their original host plant. In treatments inoculated with F1, F2, and F9, gentiopicroside content increased 33.6, 23.7 and 13% than that in the control. Strains F1, F2, and F9 could also improve polysaccharide content by more than 6.6, 18.7 and 30% compared to the control. The incidence of spot blight in gentian inoculated with F1, F2, and F9 decreased by 31.2, 26.7 and 8.5%. Inconsistent changes in the activity of the three enzymes (superoxide dismutase, catalase and peroxidase) were observed when the plants were attacked by pathogens or inoculated with fungi. High enzymatic activity did not reflect mild disease. Cross-growth period inoculation, which takes into account the original living environment (gentian plant as "substrate" and different microorganisms as symbionts) of endophytic fungi, provides a new idea for studying effects of endophytes on their original hosts. This is the first research about the role of endophytic fungi in Gentiana scabra bge. in vivo.

Endophytic fungal diversity of Fragaria vesca, a crop wild relative of strawberry, along environmental gradients within a small geographical area

BACKGROUND

Fungal endophytes are highly diverse ubiquitous asymptomatic microorganisms, some of which appear to be symbiotic. Depending on abiotic conditions and genotype of the plant, the diversity of endophytes may confer fitness benefits to plant communities.

METHODS

We studied a crop wild relative (CWR) of strawberry, along environmental gradients with a view to understand the cultivable root-derived endophytic fungi that can be evaluated for promoting growth and tolerating stress in selected plant groups. The main objectives were to understand whether: (a) suboptimal soil types are drivers for fungal distribution and diversity; (b) high pH and poor nutrient availability lead to fungal-plant associations that help deliver fitness benefits; and (c) novel fungi can be identified for their use in improving plant growth, and alleviate stress in diverse crops.

RESULTS

The study revealed that habitats with high pH and low nutrient availability have higher fungal diversity, with more rare fungi isolated from locations with chalky soil. Plants from location G were the healthiest even though soil from this location was the poorest in nutrients. Study of environmental gradients, especially extreme habitat types, may help understand the root zone fungal diversity of different functional classes. Two small in vitro pilot studies conducted with two isolates showed that endophytic fungi from suboptimal habitats can promote plant growth and fitness benefits in selected plant groups.

DISCUSSION

Targeting native plants and crop wild relatives for research offers opportunities to unearth diverse functional groups of root-derived endophytic fungi that are beneficial for crops.

Development and characterization of chloroplast microsatellite markers in a fine-leaved fescue, Festuca rubra (Poaceae)

PREMISE OF THE STUDY

Chloroplast microsatellite markers were developed for Festuca rubra to examine its population genetic characteristics, taxonomy, and coevolution with its endophyte Epichloë festucae. •

METHODS AND RESULTS

Thirteen polymorphic markers were identified from the chloroplast genome of a F. ovina accession and intergenic chloroplast sequences of F. rubra accessions. They amplified a total of 65 alleles in a sample of 93 individuals of F. rubra originating from six different populations located in the Faroe Islands, Finland, Greenland, Norway, and Spain. •

CONCLUSIONS

The developed microsatellite primer pairs can be used by researchers in population genetic and taxonomic studies, and by plant breeders in breeding programs on grasses.

Altered allocation to roots and shoots in the endophyte-infected seedlings of Puccinellia distans (Poaceae)

Endophytes play an important role in ecological and evolutionary processes in plants and have marked economic value. Seed-transmitted fungal endophytes are conventionally regarded as mutualistic symbionts, but their fitness consequences for the offspring of the host are not clear. Puccinellia distans infected with the fungus Epichloë typhina (E+) produces seeds that are several times smaller than normal (E-). This observation suggests that the E+ seedlings face a developmental disadvantage. Our growth chamber experiments compared the germination rates of the small E+ and large E- seeds of P. distans and examined the biomass allocation of seedlings to roots and shoots. The E+ seedlings germinated more slowly and maintained shorter shoots and a smaller root biomass for 30-50 days after sowing. Despite this disadvantage, the E+ plants more quickly increased their total size, attaining a larger shoot and whole-plant biomass. The shoot:root biomass ratio increased more rapidly through time in the E+ seedlings, attaining a value nine times higher in the E+ than the E- group 50 days after sowing. Such differences between the E+ and E- seedlings were not explained by the growth allometry between shoots and roots. The seedlings of P. distans infected with the Epichloë endophyte were initially handicapped by their postponed emergence, but this disadvantage was quickly overcome by their superior growth capacity. The decrease in the relative allocation to roots may indicate that endophytes increase the performance of roots as resource-acquiring organs and/or reduce the role of roots in protection against herbivores.

Genetic compatibility determines endophyte-grass combinations

Even highly mutually beneficial microbial-plant interactions, such as mycorrhizal- and rhizobial-plant exchanges, involve selfishness, cheating and power-struggles between the partners, which depending on prevailing selective pressures, lead to a continuum of interactions from antagonistic to mutualistic. Using manipulated grass-endophyte combinations in a five year common garden experiment, we show that grass genotypes and genetic mismatches constrain genetic combinations between the vertically (via host seeds) transmitted endophytes and the out-crossing host, thereby reducing infections in established grass populations. Infections were lost in both grass tillers and seedlings in F(1) and F(2) generations, respectively. Experimental plants were collected as seeds from two different environments, i.e., meadows and nearby riverbanks. Endophyte-related benefits to the host included an increased number of inflorescences, but only in meadow plants and not until the last growing season of the experiment. Our results illustrate the importance of genetic host specificity and trans-generational maternal effects on the genetic structure of a host population, which act as destabilizing forces in endophyte-grass symbioses. We propose that (1) genetic mismatches may act as a buffering mechanism against highly competitive endophyte-grass genotype combinations threatening the biodiversity of grassland communities and (2) these mismatches should be acknowledged, particularly in breeding programmes aimed at harnessing systemic and heritable endophytes to improve the agriculturally valuable characteristics of cultivars.