Resistance of Helminthosporium solani strains to the fungicides applied for tuber treatmentстатья
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Дата последнего поиска статьи во внешних источниках: 15 июля 2021 г.
Аннотация:Helminthosporium solani strains were isolated from potato tubers that were collected in Russia or taken from the imported German and Dutch seed tubers. Sequencing of the nuclear ribosomal genes and internal transcribed spacers (ITS) was done for all 16 tested strains. Obtained sequences for all 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 (azoxistrobin 250 g/l), Tecto 500 SC (thiabendazole 500g/l), Zeroxxe (colloidal silver particles (3 g/l) stabilized with amphoteric surfactant) was done. Pure cultures of the fungal strains were placed in the centre of Petri dishes containing malt agar with a fungicide at the rates of 0.1; 1; 10; 100 and 1000 mg/l (accounted for the concentration of the active ingredient). Malt agar without the 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<0.12 mg/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, azoxistrobin was effective against H. solani (EC50< 7mg/l), but there were several strains with resistance to this fungicide (EC50>100mg/l). Thiabendazole appears to be effective against the sensitive strains of H. solani (EC50 < 7,3 mg/l); however, 5 studied strains from Russia and the Netherlands were found to be extremely resistant to it (EC50>1000mg/l). The sequence of their β-tubulin gene contains a SNP mutation in 198 codon or 200 codon, translating to Gln (CAG) instead of Glu (GAG) or Tyr (TAC) instead of Phe (TTC), respectively. Thus, the resistance of the Russian, European, and American strains has the identical genetical background and is conferred by the same mutations.