Inbreeding affects ornamental traits by increasing homozygosity, and in many cases, inbreeding depression due to selfing. This study was conducted to investigate the impact of inbreeding on the expression of traits in five different genotypes of Petunia. Seeds of Petunia hybrida grandiflora Burgundy, Petunia hybrida grandiflora Blue, Petunia hybrida supercascade White, Petunia hybrida supercascade Red, and Petunia hybrida milliflora Rose morn, along with seeds from three successive selfing generations (S1, S2, and S3), were cultivated. The experiment was conducted in the greenhouse of Ferdowsi University of Mashhad from 2021 to 2023. Comparisons among different generations were performed for the five genotypes. The results indicated a significant impact of inbreeding on the reduction of flower diameter, flower count, germination percent, and total flavonoid and anthocyanin contents. This reduction became more pronounced with an increase in inbreeding generations to the extent that the most significant decrease occurred in S3. In contrast, inbreeding resulted in increased corolla tube length, stem height to the first flower, and mean germination time. Petunia hybrida supercascade white was significantly affected by selfing, with reductions of 26.17 %, 71.32 %, and 77.77% in flower diameter, flower count, and germination percent, respectively, due to inbreeding.

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