The ornamental sunflower (Helianthus annuus), native to North America, is an annual herb of the genus Helianthus in the Asteraceae family (Ogunsanya et al., 2022). The stem is upright and hollow, and the height of ornamental sunflower is about 80-100cm, a few dwarf varieties are 30-50cm, and a few tall stalk varieties are up to 200cm. The whole ornamental sunflower is setae, the leaves are ovate, helix arrangement with long stalk (Ramos et al., 2020). The head is borne at the top of the stem, also known as the flower disk. The flowers are shaped like the sun, and the flowers are huge. The flower disk has ligulate and tubular flowers (Bredeson et al., 2022). The ligulate flowers are borne at the edge of the flower disk and are asexual. The colors of ligulate flowers are yellow, milky white, orange, reddish-brown, purplish-black and other monochromatic flowers, and there are also red and yellow or mixed color flowers (Crowell et al., 2016). The petals are single or double, and the brilliant color entices insects to pollinate. The tubular flowers are located inside the ligulate flowers, are bisexual. The colors of tubular flowers are orange yellow, reddish brown and other colors (Zou et al., 2020). The tubular flowers are 15-20cm in diameter, with positive. The growth habits of ornamental sunflower are quite different from the common sunflower. The common sunflower can grow normally in the environment of temperature not less than 10℃. The normal growth of ornamental sunflower requires a daytime temperature of 21–27℃ and a nighttime temperature of not less than 10℃ (Zheng et al., 2021). The ornamental sunflower is a long-day crop, enough light to make the ornamental sunflower bloom normally. The ornamental sunflower is drought tolerance and seedling stage of the ornamental sunflower should be kept the soil moist, humidity is easy to cause the base leaves yellow. In addition, the ornamental sunflower is a cross-pollinated crop with low self-pollination rate and easy to be mixed (Wang et al., 2020).
The production cycle of ornamental sunflower is short, and it is not limited by season when planted in greenhouse. The ornamental sunflowers can be supplied every year and used as fresh cut flowers or potted ornamental plants in hotels, weddings and other places for flower arrangement (Wang et al., 2022). At the same time, the ornamental sunflower, is drought resistance and soil conditions are not strict requirements, can be planted in pieces, is a new crop for pot, courtyard and garden layout of excellent herbaceous flowers, has a high ornamental and application value (Su et al., 2019). Furthermore, the stem and flower disk of the ornamental sunflower can be used as drinking, fuel or medicine (Welcker et al., 2022).
In the early 1880s, the ornamental sunflower was used for ornamental cultivation in Europe (Shin et al., 2020). Although the cultivation history of ornamental sunflower was not long, the cultivation of ornamental sunflower developed rapidly (Sarhan et al., 2020). Dwarf, orange double petals and small flower species with strong branching had been selected from the single petal ornamental sunflower varieties. After that, European breeders turned the breeding target of ornamental sunflower to multi-color direction, and ornamental sunflower was also introduced to the international market from the European, and widely cultivated and applied around the world (Ogunsanya et al., 2022). Since the 1950s, botanical gardens in China began to introduce the ornamental sunflower from Europe, and began to focus on specimens. Since the National Flower Exposition was held in 1987, people paid attention to the small batch cultivation of the ornamental sunflower (Yang et al., 2019). However, due to the short cultivation history of ornamental sunflower in China, almost all the existing varieties are introduced from abroad or Taiwan, and the research mainly focuses on the adaptability, cultivation, radiation breeding and so on (Zhang et al., 2021).
In recent years, with the development and application of biological technology, modern breeding technology represented by molecular markers breeding has gradually become an important means of crop genetic improvement. Researches on ornamental sunflower biotechnology breeding have been carried out in China (Wang et al., 2020). The first genetic linkage map of sunflower was constructed by Genzbittel using the molecular markers of restriction fragments length polymorphism (RFLP) in 1995 (Soriano et al., 2021). Liu et al. used the random amplified polymorphism DNA (RAPD) and amplified fragments length polymorphism (AFLP) to study the genetic variation of sunflower germplasm resources, and constructed the fingerprints of sunflower with different genotypes (Koech et al., 2019). Tang et al. constructed a genetic map of sunflower recombinant inbred lines (RILs) using simple sequence repeat (SSR) markers (Ma et al., 2019). In recent years, Huang et al. constructed genetic maps of different populations of sunflowers using different molecular markers. So far, several genetic linkage maps of sunflowers have been reported at home and abroad. The purpose of continuous construction and encryption of genetic maps is to enrich the loci of the maps of sunflower, so as to provide a theoretical basis for quantitative trait locus (QTL) mapping and genetic breeding of related traits in the future. At present, there are few related reports on QTL mapping of ornamental sunflower genetic map, which needs further study.
Biological traits can be divided into quantitative traits and qualitative traits (Nakano et al., 2021). The economic traits (such as yield, stress resistance, quality) and agronomic traits of crops are mostly quantitative traits, and the locus controlling quantitative traits is called QTL (Ma et al., 2019; Marondedze et al., 2018). Classical quantitative traits are the study of multiple genes as a whole, not for single gene associated with quantitative traits of chromosomes to locate and correspondingly effect estimating. With the development of science and technology, QTLs of crops can be studied like quality traits in constructing the genetic map, effectively solved the two problems (Zhou et al., 2020). The QTL mapping is performed by locating the QTL and estimating the genetic effect of the QTL. QTL mapping is actually to detect the linkage relationship between molecular markers and loci related to quantitative traits. The basic principle is as follows: based on the genetic variation and phenotypic variation, namely by molecular markers to mark the genotypes, and to measure the phenotypic values of population traits. If the frequency distribution represents a significant difference between the groups, genotype markers and QTL are the existence of chain relationship.
In this study, we studied the related traits of ornamental sunflowers QTL mapping and the systematic analysis of genetic map, the aim is to accurately grasp the traits of ornamental sunflower varieties in best ornamental viewing period, and try to prolong the flowering through different agronomic ways, and combine with the morphological traits for different collocation display form to show the best of ornamental effect.