Obtaining Alternaria-tolerant stevia breeding genotypes in vitro

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Purpose. To obtain breeding genotypes of stevia tolerant to Alternaria alternata in vitro. Methods. Shoots of different stevia varieties (‘Berehynia’, ‘Slavutych’, and ‘Halyna’) and lines (No. 3, No. 11, No. 14, and No. 16) were cultivated on modified Murashige and Skoog (MS) medium, supplemented with Alternaria alternata culture filtrate (CF) at concentrations ranging from 10 to 100%. ‘Berehynia’ variety served as the control. Cultivation was conducted at 24 ± 2 °C with a photoperiod of 16/8 hours. Shoot viability and biometric parameters were assessed on the 3rd and 7th days. Results. A 100% CF concentration led to the death of shoots across all varieties and lines. At 10% concentration, the impact on viability was minimal, with most shoots remaining healthy and showing no changes in biometric parameters. Concentrations of 15 and 20% ensured high viability (72–95%) in all genotypes, with the best results observed for ‘Berehynia’ and ‘Slavutych’. At 25% concentration, viability decreased to 70–91%, and at 30%, to 68–90%. Concentrations from 35 to 45% reduced shoot viability to 20–63% and 20–47%, respectively, with ‘Halyna’ exhibiting the lowest values. Necrotic changes were observed at 25–45% concentrations, with the number of necrotic shoots increasing as concentration rose. Concentrations of 15–20% did not induce necrotic changes in ‘Berehynia’ and ‘Slavutych’, while in ‘Halyna’ and the lines, the number of necrotic shoots remained low. Conclusions. The addition of CF to the medium at concentrations up to 20% did not critically affect shoot viability, shoot formation ability, or biometric parameters. Increasing concentrations above 20% led to reduced shoot viability and increased numbers of necrotic plants. The ‘Berehynia’ and ‘Slavutych’ varieties demonstrated the highest tolerance, whereas ‘Halyna’ proved the most sensitive, even compared to relatively tolerant stevia lines.