RESUMO
The increased emergence of cereal stem rust in southern and western Europe, caused by the pathogen Puccinia graminis, and the prevalence of alternate (sexual) host, Berberis species, have regained attention as the sexual host may serve as source of novel pathogen variability that may pose a threat to cereal supply. The main objective of the present study was to investigate the functional role of Berberis species in the current epidemiological situation of cereal stem rust in Europe. Surveys in 11 European countries were carried out from 2018 to 2020, where aecial infections from five barberry species were collected. Phylogenetic analysis of 121 single aecial clusters of diverse origin using the elongation factor 1-α gene indicated the presence of different special forms (aka formae speciales) of P. graminis adapted to different cereal and grass species. Inoculation studies using aecial clusters from Spain, United Kingdom, and Switzerland resulted in 533 stem rust isolates sampled from wheat, barley, rye, and oat, which confirmed the presence of multiple special forms of P. graminis. Microsatellite marker analysis of a subset of 192 sexually-derived isolates recovered on wheat, barley and rye from the three populations confirmed the generation of novel genetic diversity revealed by the detection of 135 multilocus genotypes. Discriminant analysis of principal components resulted in four genetic clusters, which grouped at both local and country level. Here, we demonstrated that a variety of Berberis species may serve as functional alternate hosts for cereal stem rust fungi and highlights the increased risks that the sexual cycle may pose to cereal production in Europe, which calls for new initiatives within rust surveillance, epidemiological research and resistance breeding.
RESUMO
Metaldehyde is a molluscicide used to control slugs and snails. Despite its extensive use, very little is known about the capacity of soil microbial communities to degrade this chemical. This research provides a synopsis of the latent capacity of soil microbial communities, present in agricultural (n=14), allotment (n=4) and garden (n=10) soils, to degrade metaldehyde. Extents of 14C-metaldehyde mineralisation across all soils ranged from 17.7 to 60.0%. Pre-exposure (in situ, in the field) to metaldehyde was not observed to consistently increase extents of metaldehyde mineralisation. Where soils were augmented, (ex situ, in the laboratory) with metaldehyde (28 mg kg-1), the mineralisation capacity was increased in some, but not all, soils (uplift ranged from +0.10 to +16.9%). Results indicated that catabolic competence to degrade metaldehyde was evident in both surface (16.7-52.8%) and in sub-surface (30.0-66.4%) soil horizons. Collectively, the results suggest that catabolic competence to degrade metaldehyde was ubiquitous across a diverse range of soil environments; that varied in texture (from sand to silty clay loam), pH (6.15-8.20) and soil organic matter (SOM) content (1.2%-52.1%). Lighter texture soils, in general, were observed to have higher capacity to mineralise metaldehyde. Weak correlations between catabolic competence and soil pH and soil organic matter content were observed; it was noted that above a SOM threshold of 12% metaldehyde mineralisation was always >34%. It was concluded that the common occurrence of metaldehyde in EU waters is unlikely the consequence of low potential for this chemical to be degraded in soil. It is more likely that application regimes (quantities/timings) and meteorological drivers facilitate the transport of metaldehyde from point of application into water resources.
