Anti-herbivory defences delivered by Epichloë fungal endophytes: a quantitative review of alkaloid concentration variation among hosts and plant parts.

BACKGROUND AND AIMS: In the subfamily Poöideae (Poaceae), certain grass species possess anti-herbivore alkaloids synthesized by fungal endophytes that belong to the genus Epichloë (Clavicipitaceae). The protective role of these symbiotic endophytes can vary, depending on alkaloid concentrations within specific plant-endophyte associations and plant parts. METHODS: We conducted a literature review to identify articles containing alkaloid concentration data for various plant parts in six important pasture species, Lolium arundinaceum, Lolium perenne, Lolium pratense, Lolium multiflorum|Lolium rigidum and Festuca rubra, associated with their common endophytes. We considered the alkaloids lolines (1-aminopyrrolizidines), peramine (pyrrolopyrazines), ergovaline (ergot alkaloids) and lolitrem B (indole-diterpenes). While all these alkaloids have shown bioactivity against insect herbivores, ergovaline and lolitrem B are harmful for mammals. KEY RESULTS: Loline alkaloid levels were higher in the perennial grasses L. pratense and L. arundinaceum compared to the annual species L. multiflorum and L. rigidum, and higher in reproductive tissues than in vegetative structures. This is probably due to the greater biomass accumulation in perennial species that can result in higher endophyte mycelial biomass. Peramine concentrations were higher in L. perenne than in L. arundinaceum and not affected by plant part. This can be attributed to the high within-plant mobility of peramine. Ergovaline and lolitrem B, both hydrophobic compounds, were associated with plant parts where fungal mycelium is usually present, and their concentrations were higher in plant reproductive tissues. Only loline alkaloid data were sufficient for below-ground tissue analyses and concentrations were lower than in above-ground parts. CONCLUSIONS: Our study provides a comprehensive synthesis of fungal alkaloid variation across host grasses and plant parts, essential for understanding the endophyte-conferred defence extent. The patterns can be understood by considering endophyte growth within the plant and alkaloid mobility. Our study identifies research gaps, including the limited documentation of alkaloid presence in roots and the need to investigate the influence of different environmental conditions.

Can Aphid Herbivory Induce Intergenerational Effects of Endophyte-conferred Resistance in Grasses?

Plants have evolved mechanisms to survive herbivory. One such mechanism is the induction of defences upon attack that can operate intergenerationally. Cool-season grasses (sub-family Pooideae) obtain defences via symbiosis with vertically transmitted fungal endophytes (genus Epichloë) and can also show inducible responses. However, it is unknown whether these herbivore-induced responses can have intergenerational effects. We hypothesized that herbivory by aphids on maternal plants induces the intergenerational accumulation of endophyte-derived defensive alkaloids and resistance intensification in the progeny. We subjected mother plants symbiotic or not with Epichloë occultans, a species known for its production of anti-insect alkaloids known as lolines, to the aphid Rhopalosiphum padi. Then, we evaluated the progeny of these plants in terms of loline alkaloid concentration, resistance level (through herbivore performance), and shoot biomass. Herbivory on mother plants did not increase the concentration of lolines in seeds but it tended to affect loline concentration in progeny plants. There was an overall herbivore-induced intergenerational effect increasing the endophyte-conferred defence and resistance. Symbiotic plants were more resistant to aphids and had higher shoot biomass than their non-symbiotic counterparts. Since maternal herbivory did not affect the loline concentrations in seeds, the greater resistance of the progeny could have resulted from an inherited mechanism of epigenetic regulation. It would be interesting to elucidate the origin of this regulation since it could come from the host or the fungal symbiont. Thus, endophyte-driven differential fitness between symbiotic and non-symbiotic plants might be higher as generations pass on in presence of herbivores.

Effects of Fusarium graminearum and Fusarium poae on disease parameters, grain quality and mycotoxin contamination in barley (part II).

BACKGROUND: Barley is one of the most sown crops in the world, with multiple uses such as human consumption, animal feed and for the malting industry. This crop is affected by different diseases, such as Fusarium Head Blight (FHB), that causes losses in yield and quality. In the last years F. graminearum and F. poae were two of the most frequently isolated species in barley grains, so the aim of this study was to evaluate the interaction between these Fusarium species and the effects on disease parameters, grain quality and mycotoxin contamination on five barley genotypes under field conditions. RESULTS: Statistical differences between Fusarium treatments for some parameters depending mainly on the year/genotype were found. The results showed that the germination process was affected by both Fusarium species. As to grain quality and the different hordein fractions, it was observed that F. graminearum affects preferentially D and C-hordeins. Different concentrations of nivalenol, deoxynivalenol and their acetylated derivatives (3-acetyl deoxynivalenol (3-ADON), 15-acetyl deoxynivalenol (15-ADON)) were detected. CONCLUSIONS: In the present work, no evidence of synergism between F. graminearum and F. poae were found regarding disease parameters and mycotoxin contamination. However, at least in the years with favorable climatic conditions to FHB development and depending on the barley genotype, a continuous monitoring is deemed necessary to prevent the negative impact on protein composition and germinative parameters © 2020 Society of Chemical Industry.

Effects of Fusarium graminearum and Fusarium poae on disease parameters, grain quality and mycotoxins contamination in bread wheat (Part I).

BACKGROUND: Wheat is the most important winter crop in the world, being affected by the presence of fungal, mainly those belonging to the Fusarium genus. Fusarium head blight (FHB) is a serious disease that causes important economic damage and quantitative/qualitative losses, with Fusarium graminearum and Fusarium poae being two of the most isolated species worldwide. The present study aimed to evaluate the interaction between F. graminearum and F. poae and the effects on disease parameters, grain quality and mycotoxin contamination on five wheat genotypes under field conditions during three growing seasons. RESULTS: Statistical differences between Fusarium treatments were found for disease parameters, grain quality and mycotoxin contamination during the 2014/2015 growing season. High values of incidence (58.00 ± 8.00%), severity (6.28 ± 1.51%) and FHB index (4.72 ± 1.35) were observed for F. graminearum + F. poae treatment. Regarding grain quality, the results showed that the degradation of different protein fractions depends on each Fusarium species: glutenins were degraded preferably by F. graminearum (-70.82%), gliadins were degraded preferably by F. poae (-29.42%), whereas both protein fractions were degraded when both Fusarium species were present (-60.91% and -16.51%, respectively). Significant differences were observed for mycotoxin contamination between genotypes, with Proteo being the most affected (DON = 12.01 ± 3.67 µg g-1 ). In addition, we report that 3-ADON predominated over 15-ADON in the three seasons evaluated. CONCLUSION: Variations in plant-pathogen interaction (Fusarium-wheat pathosystem) should be considered at least in years with favorable climatic conditions for FHB development, as a result of the potential impact of this disease on grain quality and mycotoxin contamination. © 2019 Society of Chemical Industry.

Patterns and Composition of Road-Killed Wildlife in Northwest Argentina.

Roads have important effects on wildlife, such as natural habitat fragmentation and degradation and direct killing of fauna, which leads to reductions in wildlife population size. We focused on a principal road in Northwest Argentina to test for the effect of seasonality and landscape features on the composition of road-killed wildlife. We conducted regularly scheduled road trips during the dry and wet seasons. We recorded the presence or absence of a vegetation curtain or hedge along the road. We measured land use by remote sensing in a 500 m buffer along the road. We compared the abundance of animals killed between seasons (dry and wet) for different taxonomic groups (mammals, birds and reptiles) and for different origins (domestic and native). We built linear mixed models to test the effect of landscape features on the abundance of killed animals. Two hundred and ninety-three individuals were killed, belonging to 35 species; 75.8 % were native and 24.2 % domestic species. The majority of animals killed were mid-sized mammals. More animals were killed during the dry season. The most important factors to explain the wildlife road-killing were the season and the proportion of agricultural landscape. The composition of the killed animals changed with the season. The proportion of agricultural landscape incremented the number of killed birds and mammals during both seasons, without affecting reptiles. The ratio of wild to domestic animals killed was dependent on the season. This study sets a precedent as the first in road ecology in Northwest Argentina and should be taken into account for road planning and regulation.

Macro-Climatic Distribution Limits Show Both Niche Expansion and Niche Specialization among C4 Panicoids.

Grasses are ancestrally tropical understory species whose current dominance in warm open habitats is linked to the evolution of C4 photosynthesis. C4 grasses maintain high rates of photosynthesis in warm and water stressed environments, and the syndrome is considered to induce niche shifts into these habitats while adaptation to cold ones may be compromised. Global biogeographic analyses of C4 grasses have, however, concentrated on diversity patterns, while paying little attention to distributional limits. Using phylogenetic contrast analyses, we compared macro-climatic distribution limits among ~1300 grasses from the subfamily Panicoideae, which includes 4/5 of the known photosynthetic transitions in grasses. We explored whether evolution of C4 photosynthesis correlates with niche expansions, niche changes, or stasis at subfamily level and within the two tribes Paniceae and Paspaleae. We compared the climatic extremes of growing season temperatures, aridity, and mean temperatures of the coldest months. We found support for all the known biogeographic distribution patterns of C4 species, these patterns were, however, formed both by niche expansion and niche changes. The only ubiquitous response to a change in the photosynthetic pathway within Panicoideae was a niche expansion of the C4 species into regions with higher growing season temperatures, but without a withdrawal from the inherited climate niche. Other patterns varied among the tribes, as macro-climatic niche evolution in the American tribe Paspaleae differed from the pattern supported in the globally distributed tribe Paniceae and at family level.

Shifts in soil organic carbon for plantation and pasture establishment in native forests and grasslands of South America.

The replacement of native vegetation by pastures or tree plantations is increasing worldwide. Contradictory effects of these land use transitions on the direction of changes in soil organic carbon (SOC) stocks, quality, and vertical distribution have been reported, which could be explained by the characteristics of the new or prior vegetation, time since vegetation replacement, and environmental conditions. We used a series of paired-field experiments and a literature synthesis to evaluate how these factors affect SOC contents in transitions between tree- and grass-dominated (grazed) ecosystems in South America. Both our field and literature approaches showed that SOC changes (0-20 cm of depth) were independent of the initial native vegetation (forest, grassland, or savanna) but strongly dependent on the characteristics of the new vegetation (tree plantations or pastures), its age, and precipitation. Pasture establishment increased SOC contents across all our precipitation gradient and C gains were greater as pastures aged. In contrast, tree plantations increased SOC stocks in arid sites but decreased them in humid ones. However, SOC losses in humid sites were counterbalanced by the effect of plantation age, as plantations increased their SOC stocks as plantations aged. A multiple regression model including age and precipitation explained more than 50% (p < 0.01) of SOC changes observed after sowing pastures or planting trees. The only clear shift observed in the vertical distribution of SOC occurred when pastures replaced native forests, with SOC gains in the surface soil but losses at greater depths. The changes in SOC stocks occurred mainly in the silt+clay soil size fraction (MAOM), while SOC stocks in labile (POM) fraction remained relatively constant. Our results can be considered in designing strategies to increase SOC storage and soil fertility and highlight the importance of precipitation, soil depth, and age in determining SOC changes across a range of environments and land-use transitions.