Resistance of Helminthosporium solani strains to selected fungicides applied for tuber treatment

Helminthosporium solani strains were isolated from potato tubers collected in Russia or taken from imported German and Dutch seed tubers. Sequences of the nuclear ribosomal genes and internal transcribed spacers (ITS) for all 24 tested strains were identical and had 100% similarity to the sequences from GenBank identified as Helminthosporium solani. The obtained molecular data confirmed the morphological identification based on the width and length of conidia, the shape of conidiophores and the colony morphology. Screening for resistance to the fungicides Score 250 SC (active ingredient difenoconazole 250 g/l), Quadris (azoxystrobin 250 g/l), Tecto 500 SC (thiabendazole 500g/l), Zeroxxe [colloidal silver particles (3 g/l) stabilized with amphoteric surfactant] was done. Agar blocks with pure cultures of the fungal strains were placed in the centre of Petri dishes containing malt agar amended with fungicide concentrations of 0.1, 1, 10, 100 and 1000 mg/l (accounted for the concentration of the active ingredient). Malt agar free of fungicide was used as the control. Growth inhibition of 50% (EC50) compared to the control was detected based on the dose-response curves. Difenoconazole (EC50 < 0.12mg/l) and colloidal silver (EC50 < 76 mg/l) were the most effective fungicides. No strains resistant to the aforementioned fungicides were found. In most cases, azoxystrobin was effective against H. solani (EC50 < 7 mg/l), but there were several strains with high resistance to this fungicide (EC50 > 100 mg/l). Thiabendazole appears to be effective against the sensitive strains of H. solani (EC50 < 7.3 mg/l); however, six studied strains from Russia and the Netherlands were found to be extremely resistant to it (EC50 > 1000 mg/l). The sequence of their β-tubulin gene contained a SNP mutation in the 198 codon or 200 codon, translating to Gln (CAG) instead of Glu (GAG) or Tyr (TAC) instead of Phe (TTC), respectively. Thus, the resistance to thiabendazole of the Russian, European and American strains had the same genetic background and was conferred by the same mutations. © 2017, Edizioni ETS. All rights reserved

First report of Phomopsis phaseoli on tomato

[No abstract available

Resistance of Helminthosporium solani strains to selected fungicides applied for tuber treatment

Helminthosporium solani strains were isolated from potato tubers collected in Russia or taken from imported German and Dutch seed tubers. Sequences of the nuclear ribosomal genes and internal transcribed spacers (ITS) for all 24 tested strains were identical and had 100% similarity to the sequences from GenBank identified as Helminthosporium solani. The obtained molecular data confirmed the morphological identification based on the width and length of conidia, the shape of conidiophores and the colony morphology. Screening for resistance to the fungicides Score 250 SC (active ingredient difenoconazole 250 g/l), Quadris (azoxystrobin 250 g/l), Tecto 500 SC (thiabendazole 500g/l), Zeroxxe [colloidal silver particles (3 g/l) stabilized with amphoteric surfactant] was done. Agar blocks with pure cultures of the fungal strains were placed in the centre of Petri dishes containing malt agar amended with fungicide concentrations of 0.1, 1, 10, 100 and 1000 mg/l (accounted for the concentration of the active ingredient). Malt agar free of fungicide was used as the control. Growth inhibition of 50% (EC50) compared to the control was detected based on the dose-response curves. Difenoconazole (EC50 < 0.12mg/l) and colloidal silver (EC50 < 76 mg/l) were the most effective fungicides. No strains resistant to the aforementioned fungicides were found. In most cases, azoxystrobin was effective against H. solani (EC50 < 7 mg/l), but there were several strains with high resistance to this fungicide (EC50 > 100 mg/l). Thiabendazole appears to be effective against the sensitive strains of H. solani (EC50 < 7.3 mg/l); however, six studied strains from Russia and the Netherlands were found to be extremely resistant to it (EC50 > 1000 mg/l). The sequence of their β-tubulin gene contained a SNP mutation in the 198 codon or 200 codon, translating to Gln (CAG) instead of Glu (GAG) or Tyr (TAC) instead of Phe (TTC), respectively. Thus, the resistance to thiabendazole of the Russian, European and American strains had the same genetic background and was conferred by the same mutations. © 2017, Edizioni ETS. All rights reserved

Chilean regulations on metal-polluted soils: The need to advance from adapting foreign laws towards developing sovereign legislation

Chile as a major international Cu producer faces serious soil contamination issues in mining areas. Currently Chile does not have any specific law governing the maximum permissible concentrations of metals in soils to protect ecosystems and human health. Chile heavily relies on the use of environmental laws of 14 foreign countries; the choice of the country depends on the similarity of its environmental conditions with those in Chile. In this study, we used an online database to compare the similarity of Chilean rocks to those in foreign countries. Likewise, we performed soil sampling and determined the background concentrations of Cu, As, Pb, and Zn in soils of the Aconcagua basin, the largest river basin in the Valparaiso Region of central Chile. The results showed that geochemical patterns in Chile have the greatest resemblance to New Zealand, Mexico, and Italy. The background Cu concentration in the Aconcagua basin (134 mg kg−1) exceeded the legislated limits of New Zealand (100 mg kg−1) and Italy (120 mg kg−1), whereas the background Zn concentration (200 mg kg−1) exceeded the legislated limit of Italy (150 mg kg−1). Due to the elevated natural abundance of Cu and Zn in Chile, international laws should not be applied in Chile for the assessment of soil contamination. In addition, we assessed ecological risk using the results of our previous studies obtained by analyzing native field-contaminated soils of the Valparaiso region. In the Aconcagua basin, Cu posed high risk for plants in 11% of the samples, whereas As posed high risk for earthworms in 48% of the samples. We suggest that future studies are required to search for other organisms that can serve as biomarkers of metal toxicity because our previous studies were limited to plants and earthworms. Importantly, As posed high risk to human health in 25% of the samples in our study. There is a need for future studies to demonstrate empirically an association between soil As and children's blood As in order to establish the national threshold values of soil As to protect human health. We conclude that there is an urgent need in Chile to advance from the current approach of adapting foreign laws to developing Chilean sovereign environmental legislation. © 2020 Elsevier Inc

Microbial responses are unreliable indicators of copper ecotoxicity in soils contaminated by mining activities

Metal contamination of soil has become a serious environmental problem worldwide. Many studies have attempted to infer metal ecotoxicity from soil microbial responses. However, much of the data from these studies tends to be inconsistent and difficult to interpret. We hypothesized that microbial response would be a useful indicator of metal toxicity in soils contaminated by copper mining in Chile. Eighty-four topsoils (0–20 cm) were collected from three areas historically contaminated by copper mining (total Cu: 46–1106 mg kg−1, soluble Cu: 0.05–2.3 mg kg−1, pCu2+: 6.3–10, pH: 5.1–7.8, organic matter: 1.1–10%, clay: 0–28%). Based on soil metal concentrations and ecotoxicity thresholds, Cu was expected to be toxic to microorganisms in the studied soils, while the effects of other metals (total Zn: 79-672, As: 1.9–60, Pb: 19-220, Cd: 0.4–5.1 mg kg−1) were expected to be minor. Soil microbial responses (microbial biomass and numbers, nitrogen mineralization and nitrification, and community-level physiological profiles) were also measured. The results showed that the different responses of soil microbes were not correlated with each other. Furthermore, the soil microbial responses were mainly influenced by the physicochemical properties of the soil, not by the metal concentrations in the soil. The effect of copper on the microbial response was either stimulating (positive) or toxic (negative). Of the soil microbial responses measured in this study, only the microbial biomass was useful for calculating dose-response curves. However, the microbial biomass response was not consistent among the different soil copper pools (total copper, soluble copper, and activity of free Cu2+ ions). It is important to emphasize that the thresholds obtained for copper toxicity cannot be adopted in a robust manner because of the different microbial responses in different sampling areas. Thus, in the copper-contaminated soils under study, microbial response was found to be an unreliable indicator of metal toxicity. © 2022 Elsevier Lt