Patrick Materatski

A scaled-up system to evaluate zooplankton spatial avoidance and the population immediate decline concentration

Most laboratory tests may underestimate adverse effects in real scenarios of contamination because they imply the forced exposure of organisms to contaminants, thus overlooking the possibility of emigration. Avoidance from contaminants has been observed in several aquatic organisms, and avoidance-based tests have been recommended to be included in risk assessment studies. To reduce uncertainty in the extrapolation of laboratory derived results, the first aim of the present study was to compare both the median avoidance concentration and the lowest-observed-effect gradient (LOEG) values of atrazine for the cladoceran Daphnia magna, between an already developed 1.1-m-long system and a scaled-up system, three times longer. Second, the present study aimed at evaluating the population immediate decline--the proportion of the population that disappears (avoids and, if not, dies)--through the integration of the relationships between lethality and avoidance versus contaminant concentration. Daphnia magna significantly avoided atrazine, during 12-h exposures, with similar results in the original and scaled-up systems. The population immediate decline at the 48-h median lethal concentration would be 94%. Even at a concentration eliciting only 5% mortality, the population immediate decline would be over 50%. Achieving a higher pertinence of avoidance results and a better understanding of the LOEG values and their time dependence, scaling up the system further both spatially and temporally, and modeling explicit spatial dynamics in exposure and organism movement in space and time are needed.

Structural and Functional Composition of Benthic Nematode Assemblages During a Natural Recovery Process of Zostera noltii Seagrass Beds

In 2008, the stable seagrass beds of the Mira estuary (SW Portugal) disappeared completely; however, during 2009, they have begun to present early symptoms of natural recovery, characterised by a strongly heterogeneous distribution. This study was designed to investigate the spatial and temporal variability patterns of species composition, densities and trophic composition of the benthic nematode assemblages in this early recovery process, at two sampling sites with three stations each and at five sampling occasions. Because of the erratic and highly patchy seagrass recovery and the high environmental similarity of the two sampling sites, we expected within-site variability in nematode assemblages to exceed between-site variability. However, contrary to that expectation, whilst nematode genus composition was broadly similar between sites, nematode densities differed significantly between sites, and this between-site variability exceeded within-site variability. This may be linked to differences in the Zostera recovery patterns between both sites. In addition, no clear temporal patterns of nematode density, trophic composition and diversity were evident. Nematode assemblages generally resembled those of other estuarine muddy intertidal areas, which have a high tolerance of stress conditions.

Fungal endophytic communities associated to the phyllosphere of grapevine cultivars under different types of management

Fungal endophytes present in different asymptomatic grapevine plants (Vitis vinifera L.) located in different vineyards within Alentejo, a highly important viticulture region in Portugal, were identified in this study. Sampled grapevine plants included the three most representative cultivars in the region, Syrah, Cabernet Sauvignon, and Aragonez, growing under two different modes of management, conventional and biological. Sixteen fungal taxa were identified through sequencing of the internal transcribed spacer region. Total number of endophytic fungi isolated showed significant differences both in management mode and in cultivars, with higher numbers in grapevines under conventional mode and from Syrah cultivar. The composition of fungal endophytic communities did not show significant differences among cultivars, but differences were observed between fungal communities isolated from grapevines under biological or conventional modes. The most fungal taxa isolated from grapevines cultivated under biological mode were Alternaria alternata, Cladosporium sp., and Nigrospora oryzae, and under conventional mode Botrytis cinerea, Epicoccum nigrum, and Epicoccum sp. These differences suggest that the different products used in grapevine production have impacts in fungal endophytic composition. Further investigation of the identified fungi with respect to their antagonistic characteristics and potential use in plant protection to ensure food safety is now in course.

Olive Mild Mosaic Virus Coat Protein and P6 Are Suppressors of RNA Silencing, and Their Silencing Confers Resistance against OMMV

RNA silencing is an important defense mechanism in plants, yet several plant viruses encode proteins that suppress this mechanism. In this study, the genome of the Olive mild mosaic virus (OMMV) was screened for silencing suppressors. The full OMMV cDNA and 5 OMMV open reading frames (ORFs) were cloned into the Gateway binary vector pK7WG2, transformed into Agrobacterium tumefaciens, and agroinfiltrated into N. benthamiana 16C plants. CP and p6 showed suppressor activity, with CP showing significantly higher activity than p6, yet activity that was lower than the full OMMV, suggesting a complementary action of CP and p6. These viral suppressors were then used to induce OMMV resistance in plants based on RNA silencing. Two hairpin constructs targeting each suppressor were agroinfiltrated in N. benthamiana plants, which were then inoculated with OMMV RNA. When silencing of both suppressors was achieved, a significant reduction in viral accumulation and symptom attenuation was observed as compared to those of the controls, as well as to when each construct was used alone, proving them to be effective against OMMV infection. This is the first time that a silencing suppressor was found in a necrovirus, and that two independent proteins act as silencing suppressors in a virus member of the Tombusviridae family.