Comparative Assessment of Virus Elimination via Direct and Indirect Shoot-Tip Organogenesis in Purple Passion Fruit (Passiflora edulis Sims)

Three viruses, Telosma mosaic virus (TeMV), East Asian passiflora virus (EAPV), and Cucumber mosaic virus (CMV), were found to be widespread in Chinese purple passion fruit (Passiflora edulis Sims) growing regions, with co-infection by these three viruses confirmed in symptomatic field samples collected from Guilin. To evaluate the effectiveness of single shoot tip culture for virus elimination, in vitro organogenesis was examined, and both direct (DOR) and indirect (IOR) organogenesis pathways were observed. In the DOR pathway, organogenic buds and nodules were induced at a rate of 40.83%, and adventitious buds longer than 1 cm were produced by 14.86% of explants. In the IOR pathway, callus was induced at a rate of 26.67%, and a bud induction rate of 7.46% was obtained from callus-derived meristemoids. Semi-quantitative reverse transcription polymerase chain reaction (semi-qPCR) analysis revealed that viral RNA was undetectable in only a few regenerated plantlets, and none of the plantlets tested negative for two or three viruses simultaneously. The proportion of plantlets with detectable virus loss was comparable between the DOR and IOR pathways (TeMV: 5.56% vs. 11.11%; EAPV: 16.67% vs. 5.56%; CMV: 27.78% vs. 16.67%). All tested Simple Sequence Repeat (SSR) loci were monomorphic in the DOR pathway, whereas a polymorphism rate of 27.27% was observed in the IOR pathway. These findings indicate that the DOR pathway yielded only monomorphic bands at the assessed SSR loci while enabling the production of a small number of plantlets with viral RNA levels below the semi-qPCR detection limit, providing a basis for the subsequent application of more sensitive detection methods and combined treatment strategies.