Breaking the barrier of interspecific recalcitrance: a unified and efficient in vitro conservation system for Passiflora germplasm

BACKGROUND : Passiflora germplasm, characterized by rich genetic diversity, play a pivotal role in the evolutionary history of tropical crops. With the expansion of commercial passion fruit cultivation, germplasm conservation faces multiple challenges. Establishing efficient in vitro preservation systems is crucial for protecting the crop’s genetic diversity, ensuring a stable supply of breeding materials, and supporting sustainable industry development. RESULTS: This study achieves dual breakthroughs in the field of Passiflora in vitro conservation. First, a unified induction protocol was developed, enabling synchronized regulation of axillary bud induction and clustered shoot proliferation across five genetically divergent Passiflora species including edible, ornamental, and medicinal types. This breakthrough overcomes the prevalent interspecific recalcitrance that plagues in vitro culture of multiple species. The optimal conditions for axillary bud induction were identified as MS medium supplemented with 1.5 mg/L 6-Benzylaminopurine (6-BA), 0.03 mg/L Zeatin (ZT), and 0.05 mg/L indole-3-butyric acid (IBA). A modified MS-based subculture medium containing 1.75 mg/L 6-BA with the same ZT/IBA ratio achieved efficient proliferation of shoots. Second, a high-efficiency soil substrate conservation system was established for long-term conservation. Through periodic MS nutrient supplementation, the survival rate of all species exceeded 67% after 180 days conservation, with the edible species Passiflora edulis f. flavicarpa (yellow passion fruit) maintaining a survival rate at 66.1% even after 545 days. This represents a 4-fold extension of longevity compared to the traditional agar-based method, where all specimens died within 90 days. CONCLUSIONS: This technical system is simple, easy to operate, and highly efficient. It marks the first establishment of a reliable in vitro conservation method for Passiflora and provides a reference solution for the long-term in vitro conservation of clonally propagated crops.