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Abstract: In March 2021, unusual plant stuning, collar, and wet root rot of lettuce (Lactuca sativa L.) during the rosette stage was observed in two commercial fields in Serbia (44°58'N, 20°32'E; 44°45'N, 20°43'E). Disease incidence in the fields (≈ 0.9 ha each) was approximately 15 and 20%, respectively. Initial above-ground symptoms were yellowing and wilting of leaves, while below-ground symptoms were collar, wet root rot, and lesions becoming necrotic. Eventually, whole plants wilted, collapsed, and died. A total of 35 symptomatic plants were collected from the fields, and diseased tissues were cut into small pieces, surface sterilized, and plated on potato dextrose agar (PDA). Isolation resulted in 20 morphologically uniform monoconidial isolates. The isolates formed white to creamy colonies, gradually becoming salmon pink, slimy, or moist in appearance, with sparse aerial mycelia. Numerous hyphal coils with conidiophores and hyaline, smooth-surfaced, ellipsoid to ovoid, septate or aseptate conidia were formed (4.5 to 10.1×1.2 to 3.7 μm (n = 100)). To confirm the species identity, the internal transcribed spacer (ITS) region and the D1/D2 region of a selected representative isolate 13-3-c were amplified and sequenced by using primer pairs ITS1/ITS4 (White et al. 1990) and N1/N2 (O’Donnell and Gray 1995), respectively. The sequences were deposited in GenBank (ITS: OR880564 and D1/D2: OR880567). Sequence analysis revealed 100% nucleotide identity with P. cucumerina isolates from different countries deposited in the NCBI GenBank, including isolate MH860704 (Vu et al. 2019) (ITS region) and isolate KY662256 (Su et al. 2017) (D1/D2 region). Neighbor-joining analysis was conducted based on the combined ITS and D1/D2 regions, and the tree was constructed with the substitution models (1,000 bootstrap). The combined phylogeny confirmed that the sequences shared a common clade with P. cucumerina. Hence, morphological, microscopic, and molecular characterization confirmed the pathogen as P. cucumerina (Palm et al., 1995; Carlucci et al., 2012). In a pathogenicity assay, 10 isolates were tested. Five 30-day-old lettuce plants (cv. Majska Kraljica) per isolate were root-dipped in the conidial suspensions (1×105 conidia/ml). The 10 inoculated plants were transplanted into 1 L pots containing sterile substrate (Floragard, Germany). Plants treated with sterile distilled water were used as controls. Plants were maintained in a greenhouse at 25 to 28°C under a 12-hour photoperiod (Cai et al., 2021). Four weeks after inoculation, stunting, chlorosis, and wilting of plants were observed, while collars and roots exhibited typical decaying symptoms. No symptoms were observed on the control plants. The pathogen was reisolated from symptomatic tissue as previously described. Koch's postulates were completed by confirming the identity of reisolates based on morphological features. To our knowledge, this is the first report of P. cucumerina on lettuce or any other crop in Serbia. P. cucumerina is already known as a pathogen of lettuce and other hosts grown in many countries worldwide, as well as in some European countries (Belgium, England, Italy, the Netherlands, and Switzerland) (Zhang et al. 2019). This emerging pathogen may cause significant economic losses in lettuce production in Serbia and in the entire Balkan region. Our results may help to develop effective management strategies based on accurate and timely identification and regular pathogen monitoring.
Keywords: detection, identification, salat, plant diseases
Published in DiRROS: 17.05.2024; Views: 18; Downloads: 4
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Abstract: Aerosol vertical profiles are valuable inputs for the evaluation of aerosol transport models, in order to improve the understanding of aerosol pollution ventilation processes which drive the dispersion of pollutants in mountainous regions. With the aim of providing high-accuracy vertical distributions of particle mass concentration for the study of aerosol dispersion in small-scale valleys, vertical profiles of aerosol mass concentration for aerosols from different sources (including Saharan dust and local biomass burning events) were investigated over the Vipava valley, Slovenia, a representative hot-spot for complex mixtures of different aerosol types of both anthropogenic and natural origin. The analysis was based on datasets taken between 1–30 April 2016. In-situ measurements of aerosol size, absorption, and mass concentration were combined with lidar remote sensing, where vertical profiles of aerosol concentration were retrieved. Aerosol samples were characterized by SEM-EDX, to obtain aerosol morphology and chemical composition. Two cases with expected dominant presence of different specific aerosol types (mineral dust and biomass-burning aerosols) show significantly different aerosol properties and distributions within the valley. In the mineral dust case, we observed a decrease of the elevated aerosol layer height and subsequent spreading of mineral dust within the valley, while in the biomass-burning case we observed the lifting of aerosols above the planetary boundary layer (PBL). All uncertainties of size and assumed optical properties, combined, amount to the total uncertainty of aerosol mass concentrations below 30% within the valley. We have also identified the most indicative in-situ parameters for identification of aerosol type.
Keywords: valley air pollution, aerosol vertical distributions, lidar remote sensing, in-situ measurements, aerosol identification
Published in DiRROS: 03.03.2022; Views: 770; Downloads: 286
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Abstract: Eutypella parasitica R.W. Davidson and R.C. Lorenz is the causative agent of Eutypella canker of maple, a destructive disease of maples in Europe and North America. The fungus E. parasitica infects the trunk through a branch stub or bark wound. Because the fungal community may have an impact on infection and colonization by E. parasitica, the composition of fungi colonizing wood of dead branches of sycamore maple (Acer pseudoplatanus L.) was investigated in five sampling sites in Slovenia. Forty samples from each sampling site were collected between the November 2017 and March 2018 period. Isolations were made from the wood in the outer part of dead branches and from discoloured wood in the trunk that originated from a dead branch. Pure cultures were divided into morphotypes, and one representative culture per morphotype was selected for further molecular identification. From a total of 2700 cultured subsamples, 1744 fungal cultures were obtained, which were grouped into 212 morphotypes. The investigated samples were colonized by a broad spectrum of fungi. The most frequently isolated species were Eutypa maura (Fr.) Sacc., Eutypa sp. Tul. and C. Tul., Fusarium avenaceum (Fr.) Sacc., Neocucurbitaria acerina Wanas., Camporesi, E.B.G. Jones and K.D. Hyde and E. parasitica. In this study, we distinguished species diversity and the fungal community. There were no significant differences in the diversity of fungal species between the five sampling sites, and branch thickness did not prove to be a statistically significant factor in fungal species diversity. Nevertheless, relatively low Jaccard similarity index values suggested possible differences in the fungal communities from different sampling sites. This was confirmed by an analysis of similarities, which showed that the isolated fungal community distinctly differed between the five sampling sites and between the different isolation sources. Eutypella parasitica was isolated from all five investigated sampling sites, although Eutypella cankers were observed in only three sampling sites, indicating the possibility of asymptomatic infection.
Keywords: fungal composition, invasive species, diversity, fungal communities, molecular identification, frequencies, Jaccard similarity index, Eutypella parasitica, analysis of similarities, colonization
Published in DiRROS: 26.05.2020; Views: 2096; Downloads: 1239
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