Optimization of in vitro propagation and virus eradication using meristem culture and thermotherapy in two geranium species Pelargonium X hortorum ('Zonal') and Pelargonium × domesticum ('Regal').

BACKGROUND

Geraniums (Pelargonium) are among the most popular flowers worldwide. Viral infection is one of the main problems of the genus Pelargonium, and the production of virus-free mother plants is necessary for large-scale geranium propagation and exchange. Meristem culture and thermotherapy are two effective procedures that have been widely adopted to produce healthy virus-free plant stocks. The present study explores the efficiency of a combination of these two methods for virus eradication in two important Pelargonium species, Pelargonium X hortorum ('Zonal') and Pelargonium × domesticum ('Regal').

METHOD

For this purpose, RT-PCR have been performed using universal and specific primers of Tombusviridae and Bromoviridae virus families as well as Pelargonium Flower Break Virus (PFBV). Bud explants were taken from 'Zonal' and 'Regal' and were cultured in MS medium supplemented with different compositions of plant growth regulators (PGRs) as follow: A: (1 mgl Kin, 1 mgl BA, and 0.2 mgl NAA), B: (0.5 mgl Kin, 0.5 mgl BA, and 1 mgl NAA), and C: (1.5 mgl Kin and 1.5 mgl BA). After 10 days (16:8 h of light and dark photoperiod) incubation at 38 °C, the meristem (0.3 mm) of the in vitro raised plantlets were cultured on MS medium under sterile conditions. The ribonucleic acid of meristem derived plantlets was subjected to RT-PCR to detect any viral infections using universal primers for the Tombosviridae family and specific primers for PFBV species.

RESULTS

Pelargonium species exhibited varying responses to the PGR treatments. Specifically, the highest bud sprouting, plantlet regeneration, plantlet height, and root number were recorded in 'Zonal' and 'Regal' pelargoniums when cultured in media A and C, respectively. Although viral infection was confirmed in bud-derived plantlets using RT-PCR, thermotherapy and meristem culture resulted in the generation of 70% and 60% tombusviridae-free plantlets in 'Regal' and 'Zonal' Pelargoniums, respectively. The virus-free plantlets were propagated using the approved protocol.

CONCLUSION

These findings underscore the significance of utilizing suitable PGRs for in vitro regeneration of each Pelargonium species. The results of this investigation revealed that RT-PCR using universal and specific primers is a reliable sensitive virus detection procedure that coupled with culturing the heat-treated meristem can result in successful viral eradication in Pelargonium species.