The Effect of Cadmium Salts on the In Vitro Growth and Development of Sorghum (Sorghum)

Purpose. To determine the effect of different concentrations of cadmium salt on the growth and development of shoots of different sorghum species in vitro and to select tolerant forms for developing breeding genotypes resistant to abiotic factors. Methods. The study involved different sorghum species: grain, broomcorn, Sudan grass, and soryz. Sorghum bicolor cultivar 'Stepovyi 8' was used as a control. Nutrient media were prepared using the standard Murashige and Skoog (MS) formulation. Sorghum seeds were sterilized with a solution of Bilyzna (bleach). Clonal micropropagation was conducted through direct selection with the addition of cadmium chloride (CdCl₂) and cadmium sulfate (CdSO₄) at concentrations ranging from 1.0 to 45.0 mg/L. The resulting shoots were evaluated on days 3 and 7 for the percentage of viable, necrotic, and dead shoots, as well as their biometric parameters. Results. The tolerance levels of sorghum plants varied depending on the species, the type of cadmium salt, and the salt concentration. Sudan grass exhibited the highest tolerance, whereas broomcorn was the most sensitive. This trend was consistent for both cadmium chloride and cadmium sulfate. At a concentration of 10.0 mg/L CdCl₂, shoot viability remained high in all treatments (82–95%). Increasing the concentration to 15.0 mg/L reduced viability to 70–87%, while at a concentration of 20.0 mg/L, it dropped to 44–54%. Concentrations of 30.0 mg/L and higher were critical, reducing shoot viability to 2–12%. The maximum toxic concentration (45.0 mg/L) caused the death of broomcorn shoots. In comparison, CdSO₄ demonstrated lower toxicity under similar conditions. At a concentration of 10.0 mg/L, shoot viability was 90–98%, while at a concentration of 15.0 mg/L, it was 80–95%. Even at higher concentrations (20.0–25.0 mg/L), viability remained higher compared to CdCl₂, and the maximum concentrations provided survival of a small proportion of viable shoots (up to 6%). Necrotic shoots began to appear at CdCl₂ concentrations as low as 7.5 mg/L, with the highest percentage of necrosis recorded in broomcorn plants. CdSO₄ caused less necrosis, even at higher concentrations (10.0–17.5 mg/L), indicating its reduced toxicity. At low cadmium salt concentrations (1.0–5.0 mg/L), the number of newly formed shoots was high in all treatments. CdSO₄ promoted greater shoot formation compared to CdCl₂. At 1.0 mg/L, the number of new shoots ranged from 7 to 18, while at 15.0 mg/L, this number decreased to 2–10. Conclusions. CdSO₄ is a less toxic alternative to obtain viable sorghum shoots in cadmium-containing media. The best results were observed at concentrations up to 10.0 mg/L, particularly for Sudan grass and soryz. Breeding programs should consider the species-specific tolerance of sorghum to heavy metals, with special attention to Sudan grass as the most tolerant species.