The marigold (Tagetes erecta L.) is an ornamental plant with high economic value. The generation of the white flower marigold phenotype could proceed through genetic transformation with the InMYB1-CCD4ɑ gene. This study aimed to evaluate a) the regeneration of marigold leaf through indirect organogenesis, b) the transformation of callus with the InMYB1-CCD4ɑ gene, and c) analyze the InMYB1-CCD4ɑ gene presence in transgenic plantlets. Testing of shoot formation from callus continued in MS medium containing indole-3-acetic acid (IAA, 0.5 mg L^-1) with the addition of different levels of Thidiazuron-TDZ (0.25, 0.5, 0.75, and 1 mg L^-1), and 6-Benzylaminopurine, or BAP (2.5, 5, and 7 mg L^-1). BAP (7 mgL^-1) produced the highest number of shoots (six shoots per explant). In genetic transformation with A. tumefaciens harboring InMYB1-CCD4ɑ, the explants entailed pre-culturing in a bacterial suspension for one hour, co-cultivating in MS medium containing acetosyringone for 2–3 days, washing, and eliminating the Agrobacterium. Afterward, transferring explants to resting media ensued before selecting transgenic callus in the medium containing hygromycin (20 mg L^-1). The results showed the PCR analysis confirmed six plants regenerated from 24 calluses passed antibiotic selection (2.5%) and harbored the InMYB1-CCD4a gene.

Keywords: Marigold (T. erecta L.), 6-Benzylaminopurine (BAP), callus, cytokinins, hygromycin, leaf explants, Thidiazuron (TDZ), transformation efficiency

Key findings: In marigold (T. erecta L.), the optimum BAP concentration (7 mg L^-1) medium for indirect shoot organogenesis through callus of marigold leaf explants produced the highest number of shoots with shooting explant (100%) and rooting explant (11.1%). Genetic transformation protocol by using Agrobacterium was successful in establishing with the 4% of transformation efficiency at the antibiotic selection and 1% at the PCR confirmation.