Effect of BTH (benzotiadiazol in Bion 50 WG) was tested against S. sclerotiorum on cv. Iregi szürke csíkos (ISZ) and on hybrid PR64H41 (PR64) by spraying the cotyledons or true leaves of plants infected in different time scale in the greenhouse. In addition, BABA (beta-aminobutyric acid) and INA (isonicotinic acid) inducers were applied to ISZ seedlings with different concentrations (BABA 1000 and 2000 ppm, INA 100 and 200 ppm respectively). Treated (either sprayed or seed-treated) sunflowers were inoculated by placing mycelial discs (d=8 mm) on the basal part of the plants. Disease development was rated using a 0–3 scale. In the field experiment BTH was applied on cv. ISZ, PR64 and Croplan hybrids at 4–6 true leaves stage. Mycelium discs (d=5 cm) were placed on the basal part of the plants at 14 days after BTH-treatment. Disease rate was measured at 7, 14 and 28 days after inoculation (dpi). Healthy sunflower heads were also evaluated before harvesting.
According to our results in the greenhouse, spraying the cotyledons with BTH effectively restricted fungal development in PR64 hybrid but not in cv. ISZ. Applying BTH on true leaves was ineffective in this experiment against the disease. ISZ sunflowers treated at seedling stage with BABA and INA inducers showed reduced disease rates comparing to control plants. Considering results obtained in the field experiment with BTH spraying the development of sclerotinia rot was restricted at the beginning in cv. ISZ and hybrid Croplan but not in hybrid PR64. Ratio of dead plants, however, was significantly lower in all sunflower genotypes treated with BTH and infected with the fungus compared to control plants. BTH also supported the development of healthy heads (by 3–7%) in Croplan and PR64 sunflowers.
Considering our present and earlier results on the effectiveness of plant inducers to constrain Sclerotinia rot, it seems that it is highly dependent on the genotype of the host plant. Therefore, applying activators as combinations (e. g. chemical and biological) is recommended in future plant protection, but further research is essential to be carried out in order to harmonise their usage. Integrated approach (e. g. crop rotation, genetic resistance, seed dressing etc.) is crucial as well for the effective protection against S. sclerotiorum in sunflower.
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