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Risk analysis in the release of biological control agents: antagonistic Fusarium oxysporum as a case study
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Mezzi chimici per la protezione dalle malattie fungine: evoluzione delle strategie di impiego
No full textEmergence of leaf spot disease on leafy vegetable and ornamental crops caused by Paramyrothecium and Albifimbria species
No full textThe genera Paramyrothecium and Albifimbria have been established from the former genus Myrothecium and they generally comprise common soil-inhabiting and saprophytic fungi. Within these genera, only two fungi have been recognized as phytopathogenic thus far: P. roridum and A. verrucaria, both of which cause necrotic leaf spots and plant collapse. Severe leaf necrosis and plant decay have been observed in Northern and Southern Italy on leafy vegetable crops. Thirty-six strains of Paramyrothecium- and Albifimbria-like fungi were isolated from affected plants belonging to eight different species. Based on morphological characteristics, 19 strains were assigned to A. verrucaria, whereas the remaining strains, which mostly resembled Paramyrothecium-like fungi, could not be identified precisely. Molecular characterization of six loci (internal transcribed spacer [ITS], β-tubulin [tub2], calmodulin [cmdA], translation elongation factor 1-alpha [tef1], large subunit ribosomal RNA [LSU], and mitochondrial ATP 6synthase 6 [ATP6]) of the 36 new isolates and three previously ITS-characterized isolates assigned all strains to four species: A. verrucaria, P. roridum, P. foliicola, and P. nigrum. Single and concatenated phylogenetic analyses were conducted, and they clearly distinguished the isolated fungi into four different groups. A. verrucaria, P. roridum, P. foliicola, and P. nigrum were able to induce leaf necrosis singly, and they were confirmed to be the causal agents of the leaf spot disease through pathogenicity assays. The involvement of fungi previously considered saprophytic (i.e., P. foliicola and P. nigrum) in the development of plant disease for the first time deserves particular attention because of the possibility of their transmission by seeds and the limited knowledge of their management with chemicals
Risk analysis for wild type and genetically engineered antagonistic Trichoderma and Fusarium spp.
No full textAlternaria Leaf Spot Caused by Alternaria Species: An Emerging Problem on Ornamental Plants in Italy
No full textSerious outbreaks of Alternaria leaf spot and plant decay have recently been recorded on several ornamental plants in the Biella Province (Northern Italy). Twenty-two fungal isolates were obtained from Alternaria infected plant tissues from 13 ornamental hosts. All the isolates were identified morphologically as small-spored Alternaria species. Multilocus sequence typing, carried out by means of ITS, rpb2, tef1, endoPG, Alt a 1, and OPA10-2, assigned 19 isolates as Alternaria alternata, two isolates as belonging to the Alternaria arborescens species complex, and one isolate as an unknown Alternaria sp. Haplotype analyses of ornamental and reference A. alternata isolates from 12 countries identified 14 OPA10-2 and 11 endoPG haplotypes showing a relatively high haplotype diversity. A lack of host specialization or geographic distribution was observed. The host range of the studied A. alternata isolates expanded in cross-pathogenicity assays, and more aggressiveness was frequently observed on the experimental plants than on the host plants from which the fungal isolates were originally isolated. High disease severity, population expansion, intraspecies diversity, and increased range of experimental hosts were seen in the emergence of Alternaria disease on ornamentals. More epidemiological and molecular studies should be performed to better understand these diseases, taking into consideration factors such as seed transmission and ongoing climate changes
and temperatures on rice bakanae disease under controlled conditions in phytotrons
No full textBakanae disease, caused by Fusarium fujikuroi, was investigated under different CO2 and temperature environments in order to simulate climate changes in the F. fujikuroi–rice pathosystem. F. fujikuroi-infected plants were grown under six phytotron conditions: low (18/22 °C night/day), medium (22/26 °C), and high (26/30 °C) temperature, at either ambient (450 ppm) or elevated (850 ppm) CO2 concentrations. Bakanae disease index (DI), seedling death incidence, fungal DNA quantity, and chlorophyll and carbohydrate contents varied significantly in infected plants as a consequence of changes in both CO2 and temperature. Plant height and dry weight were only influenced by single factors (temperature for height, and temperature or CO2 for dry weight), and not by the CO2 × temperature interaction. Medium and high temperatures (irrespective of the CO2 level) increased the DI significantly (range from 67.5% to 95.8%) compared to low temperatures (range from 45.8% to 47.5%). Under elevated CO2 levels, noticeable differences in the expression of four rice defence-related genes and fungal DNA quantity were observed between those plants grown at higher temperatures and those at lower temperatures. Overall, combined and single effects of elevated CO2 and high temperatures seem to be favourable for bakanae disease development in the Mediterranean basin
New Approaches for Postharvest Disease Control in Europe
No full textAlternative methods to fungicide treatments have been studied in order to prevent fruit losses in the postharvest phase. Within these methods the applications of: (a) biological control agents (BCAs), (b) plant bioactive compounds, and (c) physico-chemical methods showed interesting results but still far from a practical application in Europe. Actually, despite the substantial progress obtained with BCAs, any biofungicide has been registered in Europe to control postharvest pathogens, moreover because of their insufficient and inconsistent performance. The use of plant bioactive compounds has shown that the treatment conditions (concentration, form of application, formulation, exposure time, time of treatment, etc.) can deeply influence their efficacy. The different responses found in many studies indicate a cultivar specificity in the product-pathogen-volatile interaction. A barrier to use the plant bioactive compounds may not be efficacy, but rather the off-odours caused in fruits and vegetables and/or the phytotoxicity. Physico-chemical methods include heat, ionising and ultraviolet C irradiation, food additives inducers of resistance. Heat treatments by hot water dips, hot dry air, vapour heat or very short water rinse and brushing appear promising. To overcome the drawbacks that have arisen with the these methods, the integration of the antagonist with other treatments such as low toxic substances (GRAS), heat, etc. has been proposed; this strategy could produce an additive or synergistic effect on disease control and obtain satisfactory levels of disease reduction
First Report of Fusarium Wilt on Orange Coneflower (<i>Rudbeckia fulgida</i>) in Northern Italy
Full text linkOrange coneflower (Rudbeckia fulgida) of the Asteraceae family is widely used as an ornamental plant in public and private gardens. At the end of the summer of 2016, in a garden in Biella Province (northern Italy, elevation 850 m, 45°36′00′′ N, 8°03′00′′ E), a previously unknown wilt was observed on 7-month-old plants. The disease affected 70% of about 30 plants grown in mixed borders and in pots. Affected plants were stunted and developed yellow leaves followed by wilting of basal leaves and stems. A continuous brown to black streak in the vascular tissue of roots, crown, and basal stem was observed. Tissues were excised from the vascular system of the crown and stem of 10 symptomatic plants, immersed in a solution containing 1% sodium hypochlorite for 1 min, rinsed in sterile water, then cultured on potato dextrose agar medium (PDA) amended with 25 mg/liter of streptomycin sulfate. After 6 days at 23°C, 80% of the obtained fungal colony were similar and developed a cottony mycelium with a purple pigmentation. The fungus was morphologically identified as Fusarium sp. (Leslie and Summerell 2006) by combining the macroscopic observation on PDA, the type of high quality and quantity symptoms on diseased plants, and the part of the plants from which the strains were obtained using isolation protocols. One representative isolate (IT22) was subcultured onto PDA and a single-spore culture was obtained. On carnation leaf agar (CLA), these single-spore isolates produced 3-septate macroconidia of 23.1 to 33.9 × 2.9 to 4.5 (average 28.8 × 4.1) μm in orange sporodochia from monophialides (13.4 to 21.3 and 2.1 to 2.7) on branched conidiophores. Microconidia were elliptical or reniform (6.5 to 14.0 × 2.4 to 4.2, average 10.3 × 3.4 μm). Chlamydospores formed either terminally or intercalary and measured 7.1 to 9.6 (average 8.2 μm). DNA from isolate IT22 was obtained using E.Z.N.A. Fungal DNA Mini Kit (Omega Bio-Tek, Darmstadt, Germany), EF1/EF2 primers were used to amplify the elongation factor-1 alpha gene region from the extracted DNA (O’Donnell et al. 1998). The amplicon was sequenced (GenBank accession no. KY563701) at the BMR Genomics Centre (Padua, Italy). A BLASTn search of the 685 bp amplicon was 100% identical to that of the NRRL_52787 isolate of Fusarium oxysporum (JF740855.1). Pathogenicity tests were carried out on healthy, 60-day-old plants of R. fulgida inoculated by root immersion in conidial suspension (1 × 107 conidia/ml) of the IT22 isolate and transplanted into 2 liter pots filled with steam-sterilized soil. Noninoculated plants served as control. Plants (six per treatment) were kept in a glasshouse at an average temperature of 24°C (minimum 20, maximum 28°C). The pathogenicity test was carried out twice. Wilt symptoms and vascular discoloration in the roots, crown, and veins developed within 20 days on all inoculated plants, while noninoculated plants remained healthy. F. oxysporum was consistently reisolated from infected plants only. F. oxysporum has been reported on R. hirta in Florida (Alfieri et al. 1994). Marois and Norcini (2003) also isolated an F. oxysporum from seeds of wild plants of R. hirta, providing the evidence of the role of contaminated seed source in survival of the pathogen. This is the first report of F. oxysporum on R. fulgida in Italy, as well as in the world. Further studies are needed to identify the host range and the forma specialis of the Italian isolates
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