Plants interact with a myriad of microorganisms that modulate their interactions within the community. A well-described example is the symbiosis between grasses and Epichloë fungal endophytes that protects host plants from herbivores. It is suggested that these symbionts could play a protective role for plants against pathogens through the regulation of their growth and development and/or the induction of host defences. However, other endophyte-mediated ecological mechanisms involved in disease avoidance have been scarcely explored. Here we studied the endophyte impact on plant disease caused by the biotrophic fungus, Claviceps purpurea, under field conditions through (1) changes in the survival of the pathogen´s resistance structure (sclerotia) during overwintering on the soil surface, and (2) effects on insects responsible for the transportation of pathogen spores. This latter mechanism is tested through a visitor exclusion treatment and the measurement of plant volatile cues. We found no significant effects of the endophyte on the survival of sclerotia and thus on disease inocula. However, both pathogen incidence and severity were twofold lower in endophyte-symbiotic plants than in non-symbiotic ones, though when insect visits were prevented this difference disappeared. Endophyte-symbiotic and non-symbiotic plots presented different emission patterns of volatiles suggesting that they can play a role in this protection. We show a novel indirect ecological mechanism by which endophytes can defend host grasses against diseases through negatively interacting with intermediary vectors of the epidemic process.
Chronic anthropogenic stress agents include the different tillage systems, which usually influence the population metrics of cryptofauna communities. Among them, the edaphic mesofauna is sensitive to natural and anthropogenic disturbances of the environment, producing changes in its specific composition and abundance. This allows us to select it as an indicator of disturbances generated in the stability of the ecosystem by land use. Taking these into consideration, the objective of this work was to study the effect of the degree of artificialization in land use on the stability of the agroecosystem through mesofauna. The study area was located in an environment of peripheral hills of the district of Azul. Four sites were selected in similar geoenvironments, with different degrees of artificialization of land use. Edaphic parameters were analysed in each site, and mesofauna individuals were identified through keys for population analysis. Mesofauna population metrics were analysed. Biological indicators were applied. Through mesofauna it was possible to differentiate sites with different degrees of artificialization by land use. Biological indicators allowed us to determine the stability of agroecosystems.
Background: Intraspecific variations in floral traits of species over its geographic range can be associated with differences in pollinator assemblages and/or with environmental conditions. Aims: We evaluated the area of elaiophores in different populations of Stigmaphyllon bonariense (n = 9) and S. jatrophifolium (n = 6), and we hypothesised a marked reduction in their size towards their southern limits of distribution, associated with different oil-collecting bee assemblages. Methods: Area of elaiophores was calculated and we carried out linear correlations with floral size, pollinators, visitation rate and pollinator size along the latitudinal gradient of the plants' distributions. Moreover, we examined the relative size relationships using allometric analyses, to verify this reduction. Results: Floral elaiophore area decreased with latitude. However, for S. bonariense we observed an allometric reduction in elaiophore area with respect to floral size, while for S. jatrophifolium an isometric reduction was found. In both species, pollinator richness and visitation rate did not diminish with latitude, but pollinator size for S. bonariense varied. Conclusions: Our results show a reduction in the size of elaiophores in both species along their distribution range, with dissimilar tendencies, suggesting that these species may have different selection pressures that cause variation of their phenotypic traits.
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