Roses have gained the name of “queen of flowers” due to their floral characteristic and plant habits. Roses have been grown and bred to serve for indoor plants, cut flowers, landscaping, and essential oils. Miniatures are a group of rose families that have all the characteristics of a standard rose but are dwarfs in all respect. The roses sold for indoor use are known as “pot rose” that can be used more versatile than other roses. They have different flower types, colors, and forms (Rubert, 1977) and are among the ornamental plants whose demand has increased day by day. Pot roses rank among the top two pot flowers and are worth approximately 14.3 million euros, and 15.7 million pieces of pot miniature roses were sold in worldwide pot flower sales according to Royal FloraHolland (2020) (Flora Cultural International, 2021). The increasing consumer demand for potted miniature roses motivates the breeders into the breeding programs and successfully improves many new miniature rose cultivars.

The development of new rose varieties involves high investment and labor. Therefore, there is a constant need for genetically improved breeding to combat conditions and for scientifically rigorous evaluation of inheritance processes to adequately document rose breeding. Crossing between closely related varieties with common ancestry obtains better results, which is commercially desirable; however, compatibility barriers may limit crossing success (Younis et al., 2014). Other problems include sterility and non-fertility of pollen donor parents. Therefore, breeders desire to integrate fertile parents into gene pools. Flower color, flower size, the number of petals, plant habit, fragrance, the number of flowers per stem, and flower longevity are the primary selection criteria in potted miniature rose breeding. Many rose cultivars have been developed with classical breeding approaches until today. These cultivars certainly ensure the criteria of the breeder for desirable traits, but gene crossing was limited. As a result, less variation in cytology-occurred compatibility decreased among candidate cultivars. Moreover, genetic barriers to hybridization are often an obstacle to obtaining interspecific hybrids in rose (Abdolmohammadi et al., 2014; Dogan et al., 2022). Furthermore, potted miniature roses have not a rich source of pollen for pollinators, and miniatures are known for their difficult sexual reproduction from pollination to seed set and germination (Datta, 2018). Therefore, although some researchers have reported that miniature roses got mini roses when crossed with climber, floribunda, cut flowers, or bush roses (Datta, 2018), in miniature rose breeding, less attention has been paid to scientifically rigorous studies on the quantitative and qualitative traits in their hybrids.

The present study aimed to cross the potential of some miniature rose varieties to compare crossability among the cultivars and the morphology of hybrid progeny.

In breeding programs, the development of new rose varieties follows a sequence of processes such as fertilization, fruit set, seed formation, germination of seeds, and hybrid progeny after controlled pollination (Nadeem et al., 2013; Dogan et al., 2020). One of the most important steps in crossbreeding is the inclusion of fertile species and varieties in breeding programs. It is very important that the pollinator pollen, which is used as a male parent, is highly viable and germinating. In the studies carried out, the viability rates of some modern roses were found between 17.71% and 52.14% by Dogan (2022), and Pipino et al. (2011) reported that it ranged from 0% to 46.5%. The pollen germination rates of different hybrid tea roses were determined between 0% and 46.5% by Pipino et al. (2011), and Dogan et al. (2020) found that it varies between 24.61% and 45.24%. These studies show similarities with the present study. Although the fruit set, the number of seeds per fruit, and the seed germination rate of miniature roses are generally low, the miniature used as pollen parents and crossed with climbers, floribundas, and shrub roses is recommended (Datta, 2018; Dogan, 2022). In the present study, fertility of the parent cultivars ranged from low to high, most likely caused of multiple genetic factors, mitotic abnormalities, including lethal genes and their deleterious effects, incompatibility of gametes, the heterozygous polyploid, and interspecific factors of parent cultivars (Ogilvie et al., 1991). Overall, there was a satisfactory success rate of 39.58% among all possible crosses, which coincides with the findings of Dogan (2022) and Uran (2022) who observed that 30.3% and 37.92%, respectively, of all miniature crosses develop into mature hips, and the resulting seeds exhibit a germination rate of 18.49%. Cross-incompatibility and disparities at the ploidy level could cause low hip-set percentages in most tetraploid roses. In this regard, the present study is consistent with the findings of other researchers (Morey, 1959; Rajapakse et al., 2001; Kazaz et al., 2020; Dogan et al., 2022). Fagerlind (1954) reported that, although the union of gametes from both parents could occur, not all hybrids might necessarily have a good seed set or viable embryos. Otherwise, environmental conditions (daylight and daily temperature) might affect the seed set and the germination percentage (Gudin et al., 1990). Some growth inhibitors may develop in rose seeds that block seed germination. These inhibitors include abscisic acid in the pericarp and testa, which are physiological barriers in the embryo (Bo et al., 1993; Zhou et al., 2009). Some research studies have reported that hybrid tea roses have a low (below 50%) and non-uniform germination rate (Gudin, 2003; Ueda, 2003; Zlesak, 2005; Anderson and Byrne, 2007). In potted miniature rose breeding, the seed set of miniature roses is generally low. The situation is that the dwarf factor causes infertility in females (Datta, 2018). It has been reported that miniature roses produce few fruits and seeds per fruit when used as the female parent in breeding programs, and the seed germination rate is low. The reason why the seed formation rate of miniature roses is generally low in potted miniature rose breeding may be due to the fact that the dwarfness causes infertility in females. On the other hand, Datta (2018) stated that the fertility of miniature roses is high when used as pollen parents, and a good fruit formation, the number of seeds per fruit, and the germination rate can be obtained when hybridized with climbers, floribundas, or shrub roses. In addition, although many researchers reported that the difference in the number of seeds per fruit was due to different pollen viability and germination rates of the parents, it was reported that wild and old garden roses had a higher pollen quality than hybrid roses, which increased fruit formation and the number of seeds per fruit (Ueda and Hirata, 1989; Gudin et al., 1991; Zlesak et al., 2007; Kazaz et al., 2020). Love et al. (2016) reported that especially the compatibility of the parents affects the success of crossbreeding. In addition, studies have reported that high fruit sets and seed numbers are obtained in parallel with the increase in the amount of pollen applied to the stigma (Falque et al., 1995). Atram et al. (2015) determined that stigma diameter and fruit-bearing capacity affect especially the fruit set and the average number per fruit in roses.

These findings suggest that even species or varieties with a high female crossability rate may not always exhibit great seed efficiency. These many parent–offspring connections and pairings highlight the significance of pollen fertility. However, as a female parent, in miniature roses, the fertility affected the crossing success as much as pollen fertility. Considering that miniature roses with small flower diameters may have less stigma, they had lower seed formation than other modern roses. It has been reported that fruit formation, the number of seeds per fruit, and seed formation are lower in interspecies crosses than that in intraspecies crosses (Kılıç, 2023). Successful results were obtained in fruit formation, the number of seeds per fruit, and seed formation by crossbreeding between species in miniature roses with limited fertility. Considering that seed formation is negligible from hybridization of miniature roses with miniature roses, it can be said that seed formation is related to cross-compatibility rather than the stigma number and pollen germination rates. Both the germination rates of seeds obtained from the combinations of R. centifolia and those of Black Baccara did not differ from one another. However, the embryo rescue procedure will improve the likelihood of producing additional hybrids if the old garden roses have post-pollination barriers. The study showed the crossing success of the miniature roses as seed parents. Moreover, there were limited studies in miniature rose breeding. It is thought that this parameter is important for evaluating breeding studies. The inbreeding tendencies of new cultivars could be derived from a small number of productive genotypes with above-average progeny (De Vries and Dubois, 1996). Treatment results in inbreeding depression due to increased homozygosity in the resulting lines and consistency of lethal alleles (Ogilvie et al., 1991). Seedling growth took only 8 weeks to complete vegetative growth and flowering thereafter. Miniature rose progenies (F₁) of set flowers on completion of juvenility last for 4 to 5 weeks. According to the study, there was a significant association between the weight of the fruit and the quantity of seeds present in each fruit. This is to be expected because the fruit will be heavier with more seeds. Although less strong, there was still a significant relationship between the fruit set and seed germination. This shows that the fruit set and germination have a genetic component but shows that other factors, such environmental conditions, also play a role.

Some parameters in qualitative and quantitative traits were evaluated in parents and hybrid cultivars. These features were evaluated by statistical analysis and the creation of a dendrogram for various qualitative and quantitative characters. Some features have improved positively achieving the purpose of the study, whereas some features remained unchanged. Using the dendrogram approach given in the current study, yield characteristics of some rose varieties were investigated in terms of morphological characteristics and other quantitative characteristics and get similar findings to found in progenies (Nadeem et al., 2015). The plant heights of the F₁ plants obtained in the combinations showed variation. Although the pollen parents in these combinations were tall, the reason why the F₁ plants remained between 20 cm and 26.62 cm might be due to the dominant effect of the dwarf gene. Indeed, it has been reported that a dwarf gene locus is controlled by a dominant (D) allele gene (Debener, 1999) and, when crossed with miniature, 90% of progeny are expected to be miniature (Datta, 2018). In addition, Byrne (2009) determined that additive genes are effective in terms of plant height that is inherited by polygenic genes. Although the data obtained in the present study in terms of flower diameter are generally similar to the flower diameters of commercial potted miniature roses, the differences in the lower and upper values of the flower diameter size may be caused by the climatic conditions in which the plants are grown, the pot size, the growing environment, the plant growth regulator application, and the differences in cultural processes. In addition, flower diameter is directly related to the number of petals, and the number of petals is controlled by dominant genes (Morey, 1959; Zlesak, 2007). In the present study quantity of petals were double flowers in all roses. Double flowers were all inherited through a single dominant allele, and additive genes stated the number of petal in double genotype (Debener, 2003). The data also reveal that the F₁ hybrids and their parents had significantly different heights of the plants, flower diameters, and number of petals. The F₁ hybrids had more petals and greater flower diameters than their parents, and they were often taller than their parents. This shows that the F₁ hybrids have heterosis or hybrid vigor. Some of the F₁ hybrids had longer flower persistence life than the parents, whereas others had shorter flower persistence life. Overall, the F1 hybrids in the study had a number of desirable traits, such as larger flower diameters and more petals. These traits are likely due to heterosis or hybrid vigor. However, the data also suggest that the flower persistence life is a more complex trait that is influenced by multiple genes.

Rose colors are due to the presence of pigments like anthocyanin, carotenoids, and flavonols. The anthocyanidins (peonidin, pelargonidin, and cyanidin) ensure a typical color, specially red-colored or purple-colored flowers. The flower color is commonly due to additive gene action of several genes or different kinds of pigments. Rose color has a complex inheritance due to the additive gene action. For instance, the inheritance of the pink flower of R. multiflora is controlled by one or two complementary genes. Whereas the pink color is dominant to the red or dark red color, similarly, the light yellow is dominant to the dark yellow and white color is recessive to light yellow and cream (Lammerts, 1945). Debener and Mattiesch (1999) obtained F₁ plants with 22.12% white and 77.88% pink petal leaves by crossing two different pink rose genotypes and also determined that pink color may have monogenic or oligogenic inheritance. In a study conducted by crossing pink and white rose genotypes, it was determined that 31.58% of F₁ genotypes had white petals and 68.42% had pink petals (Shupert, 2005). These study findings were consistent with those in the present study.

The fact that F₁ progeny often has a similar height to the phenotypic of the main parent can be considered an important component in the production of this characteristic, and the use of tiny roses as the seed parent in miniature rose breeding plays an important part in parent selection. The use of R. centifolia as pollen parent resulted in obtaining fragrant rose genotypes. Genotypes with large buds were generated by using the Black Baccara variety, which is one of the cut rose varieties, and the use of cut roses in miniature rose breeding as parents can be provided to the offspring in terms of attractive flower color and leaf brightness.

Breeding studies require a long time and more labor and are costly. The development period for potted miniature roses is 4–5 years; therefore, the characteristics and fertility situations of parents are very important in the selection of hybrid combinations. The present study shows high rates of fruit, many seeds per fruit, and a low germination ratio, a few progeny were obtained while these genotypes had dwarf and large flower diameter plants. In the combinations where R. centifolia was used as a pollen parent, fragrant plants get the result that Rose Bling Love Star and Rose White Star have the potential to be utilized as a seed parent, as evidenced by the high fruit set and the number of seeds per fruit. Moreover, qualitative and quantitative of the progenies and calculations of heterosis and heterobeltiosis had proven to be useful tools in evaluating the performance of the offspring on the parents, thus facilitating the selection of cultivar candidates with better-performing traits. Because of the fact that cross-combinations can be determined using the information on parental performance that is now accessible, this study is assumed to help with the breeding success of the miniature roses. In comparison with a random decision, the combinations chosen in this manner are more likely to be successful. Breeders can swiftly adopt the practice of choosing their cross-combinations and parents more carefully to increase the efficacy of their breeding programs and offer more new types to their market.

The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author.

The author confirms being the sole contributor of this work and has approved it for publication.