Putrescine-Mediated Modulation of Morphological and Reproductive Differentiation During Direct In Vitro Regeneration of Rosa chinensis cv. Old Blush

In vitro regeneration and flowering systems provide valuable platforms for rose breeding and biotechnological applications. Although the effects of plant growth regulators (PGRs) on Rose regeneration have been extensively studied, the contribution of growth additives, either alone or in combination with PGRs, remains insufficiently understood in Rosa chinensis. This study investigated the effects of PGRs (6-Benzylaminopurine (BAP), 1-Naphthaleneacetic acid (NAA), and indole-butyric acid (IBA)) combined with three growth additives, putrescine (Put), phloroglucinol (PG), and casein hydrolysate (CH), at different concentrations on the vegetative and reproductive responses of R. chinensis in an in vitro system. No flowering occurred in media without PGRs, regardless of the growth additive treatment, highlighting the essential role of PGRs in floral induction. However, the integration of growth additives with PGRs significantly enhanced regeneration and flowering performance. Among the tested additives, Put showed the strongest stimulatory effect, increasing in vitro flower production and improving floral characteristics. PG promoted several morphological traits, including shoot regeneration and flower stem elongation, but was less effective than Put. CH exhibited limited effects on both vegetative growth and reproductive development. These findings indicate that Put supplementation in PGR-based media is an effective approach for improving regeneration and flowering efficiency in R. chinensis, with potential applications in rose biotechnology and breeding programs.