Study on key techniques for virus-free rapid propagation of Xinjiang Zaohuang fig using apical meristem tissue culture

【Objective】Xinjiang Zaohuang fig (Ficus carica L.) is a predominantly cultivated variety in Atux, Xinjiang, prized for its thin-skinned, seedless fruit, tender flesh, sweet flavor, and high nutritional and medicinal value, garnering widespread acclaim in both domestic and international markets. In response to the severe viral disease affecting the Xinjiang Zaohuang fig and the urgent need to establish a shoot tip culture system for virus elimination, efforts have been made to detoxify the fig through shoot tip culture. The aim is to establish a shoot tip culture system for virus elimination in figs, providing technical support for further exploration of fig viral diseases and the cultivation of virus- free seedlings. 【Methods】The preliminary detection of virus types carried by fig seedlings was conducted using highthroughput sequencing. The initial virus screening revealed that figs mainly harbor eight types of viruses, including FBV-1 (Fig badnavirus 1), FBV-2 (Fig badnavirus 2), and GBV (Grapevine badna FI virus). Shoot tip culture for virus elimination was performed on the detected viruses. The test materials were tissue- cultured seedlings after three generations of subculture. Under a microscope in a clean bench, the apical meristem tips were excised using a dissection needle, with a length of 0.8 to 1 mm. Af-ter excision, the tips were transferred to callus induction medium for callus induction culture. The medium composition was: MS + 1.5 mg ·L-1 TDZ + 0.1 mg ·L-1 NAA. The study investigated the effects of different concentration ratios of hormones such as 6-BA and NAA on apex induction to screen out the optimal concentration for the apex tissue culture system. Finally, the detoxification effect of the apex was detected using high-throughput sequencing. In the acquisition of explants, the innovation of this experiment laid in initially subjecting the collected stem segments to primary subculture under sterile conditions before taking shoot tips from the healthy tissue-cultured seedlings. This method not only significantly reduced the contamination rate of the explants, but also decreased the workload of explant disinfection. The tissue-cultured seedlings thus cultivated provided ample raw materials for the shoot tip tissue culture experiments.【Results】In the shoot tip induction experiment, the optimal medium type was MS; the optimal concentration ratio for callus induction was MS + 1.5 mg·L-1 TDZ + 0.1 mg·L-1 NAA, with an induction rate of 88.6%. The callus morphology was favorable, predominantly light green, and the callus formation primarily occurred inside the explants in contact with the medium. The optimal concentration ratio for adventitious bud induction was MS + 2.0 mg·L-1 6-BA + 0.05 mg·L-1 NAA, resulting in bright green adventitious buds with robust growth and a proliferation coefficient of 3.60. The optimal concentration ratio for adventitious bud rooting induction was 1/2 MS + 1.0 mg·L-1 IBA + 0.5 mg·L-1 NAA, achieving a rooting rate of 67.68%, with an average root number of 3.55. The root growth was excellent, with lateral and fibrous roots developing. After shoot tip detoxification, only three viruses showed removal effects. FBV-1 had the best removal effect, with a detoxification rate of 52%, while FBV- 2 and GBV had detoxification rates of 43% and 50% , respectively. The detoxified seedlings screened after detoxification detection underwent rooting and transplanting experiments. Fig tissue-cultured seedlings that had undergone 40 days of rooting induction were acclimatized in a greenhouse for 10 days before being transplanted into nutrient pots. It was observed that a significant number of fig tissue-cultured seedlings began to die 7 days after transplanting, with mortality increasing over time. After 30 days, the mortality rate stabilized, with a survival rate of 54.86%. The surviving plants grew well, with an average plant height of about 9 cm and an average root length of about 7 cm. After 60 days, the roots were robust, and the plant height increased to about 16 cm, with an average root length of about 11 cm, achieving full soil stabilization. By 70 days after transplanting, the average plant height was about 19 cm, and the average root length was about 12 cm. At this stage, the survival rate of the fig seedlings was 44.34%, with overall robust growth.【Conclusion】In the acquisition of explants, the innovation of this experiment lies in initially subjecting the collected stem segments to primary subculture under sterile conditions before taking shoot tips from the healthy tissue-cultured seedlings. This method not only significantly reduces the contamination rate of the explants, but also decreases the workload of explant disinfection. The tissue-cultured seedlings thus cultivated provide ample raw materials for the shoot tip tissue culture experiments. Additionally, the successful acclimatization and transplantation of detoxified seedlings have been achieved. Through proliferation and expansion, a large number of detoxified seedlings can be obtained in a relatively short period of time, thereby meeting the demands for large scale production. However, this process requires a lengthy cultivation cycle as a foundation, supplemented by a stringent inspection system to ensure the quality and health status of the detoxified seedlings.