| Sumario: | White yam (Dioscorea rotundata) is an important staple food and an income-generating crop in tropical regions. However, its genetic improvement via classical breeding is challenging and time-consuming due to an erratic flowering pattern, poor seed set, dioecious nature, low pollen fertility, and low seed germination rates. These constraints limit the genetic gains achievable in each generation and prolong the breeding cycle to approximately 10 years, underscoring the need to implement faster biotechnological approaches. This study presents an optimized protocol for producing friable embryogenic callus (FEC) in yam, which serves as an ideal tissue type for transgene delivery and genome editing using site-specific nucleases. The various factors influencing FEC induction were optimised, including basal salt composition, tissue wounding, washing treatments, and medium supplementation with antioxidants. The results demonstrated that reducing the concentration of nitrogen supplements and enriching the medium with 10 mg/L thiamine, 1000 mg/L proline, and 600 mg/L casein hydrolysate increased callus fresh weight to 498.4 mg per explant and enhanced the embryogenic competence to 76.2%. Callus wounding by crushing through mesh further improved FEC induction, and washing the crushed callus with 10 mg/L ascorbic acid reduced browning and necrosis, reducing recovery time from 25 to 13 days. The optimized FEC induction medium (FIM) induced somatic embryos in over 77% of cultures. This protocol provides a robust platform for yam genetic transformation, offering an excellent starting material for protoplast isolation, regeneration, and genome editing to enhance crop resilience and productivity.
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