# Flowering Stage and Daytime Affect Scent Emission of _Malus ioeensis_ \"Prairie Rose\"
## 1 Introduction  
Floral scent compounds are secondary metabolites released by plant flowers. These are mainly volatile compounds with low molecular weight (generally less than 300 Dalton), such as terpenoids, benzes/phenylpropanoids, aliphhtics, and some nitrogen- and sulfur-containing compounds [1]. The floral scent is an important expression signal for plants to induce insect pollination, as well as an important quality indicator for evaluating ornamental plants and cut flowers [2]. Studies had shown that floral scent had a greater influence on consumers than flower color and shape [3]. However, most of the common flower-breeding goals are concentrated on flower shape, flower color, and flowering time, with the result that flowers are not bred for fragrance [4], and many cultivated flowers have gradually lost their aroma [5].  
Flowering crabapple (_Malus_) is an important ornamental flower in the northern temperate zone [6]. China is the distribution center of _Malus_[7; 8], but the long-term and widespread use of cultivars is mainly limited to a few species, such as _M. hulliana_, _M. micromalus_ and _M. Inupensis_. Many precious crabapple germplasm resources have not been fully applied. The traditional view in China is that flowering crabapple flowers is beautiful but not fragrant [9]. However, long-term natural selection and artificial breeding have resulted in more than 700 crabapple cultivars worldwide [10; 11; 12], most of which are aromatic [9]. [PERSON] et al. [9] measured the floral compounds of 17 crabapple cultivars and found that the main compounds were 3-methyl-1-butanol, octene, benzyl alcohol, 3-methyl-4-oxo-penta acid, and heptane. [PERSON] [13] examined the floral and leaf compounds of _M. bracata_ and found that the compounds responsible for the floral scent were mainly butylated hydroxytoluene, heptadecane, hexadecane, \(\alpha\)-farnesene and \(\beta\)-octene. [PERSON] et al. [14] used electronic nose and gas chromatography-mass spectrometry to measure the different aroma intensities of crabapple and initially explored the relationship between the scent compounds and the electronic nose. At present, research on crabapple floral scent is far behind research on the flowering period [15], flower color [16; 17], flower shape [10] and pollen [18], and there are no reports on the release characteristic of crabapple floral scent. In fact, a plant often has more than one dozen to hundreds of volatile compounds, and these compounds and the associated level of scent emission change with flower age, endogenous circadian rhythms, pollination status, and environmental conditions (such as moisture, light, and temperature) [19; 20; 21]. There are no two floral scents that are exactly the same, even among plants with similar flower shape and color, due to the large diversity of volatile compounds and their relative abundance and interaction [22; 23]. Thus, when carrying out fragrant flower breeding or floral regulation, even essential oil extraction, it is vital to understand the floral scent properties of a plant and the associated release dynamics.  
We used _M. ioensis_ \"Prairie Rose\" as materials, which has strong scent and beautiful rose-like flower shape, to compare the difference of volatile compounds of flower at different flowering stages and day-night times using headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS). Our objective is to explore the floral scent characteristics and release dynamics of _M. ioensis_ \"Prairie Rose\".