## 1 Introduction  
Tea, as a widely consumed non-alcoholic beverage, is associated with various health benefits, such as anti-inflammatory, anti-tumorigenic, and cardio-protective effects [1]. It is made from the fresh leaves of tea plants (_Camellia sinensis_. L) that contain abundant secondary metabolites. In addition to the taste sensory of tea, the aroma is also an important factor in consumer preference. There are many types of aroma characteristics of different teas, such as toasty, floral, fruity, nutty, fresh and brisk aroma, etc. [2; 3; 4], the formation of which are impacted by various factors, such as processing method, tea cultivar, growing conditions, and harvest season [5; 6; 7; 8; 9; 10; 11]. Green tea (non-oxidized tea) and black tea (fully oxidized tea) are widely consumed over the world and have different sensory properties. Even for the same type of tea, there are many different scent types. For example, green tea has scent types of floral, fruity, nutty, chestnut-like fragrances, and so on [3; 8]. Generally, the aroma quality of dry teas is associated with processing techniques, considering the chemical conversions that occur during processing, resulting in the lost or postharvest synthesis of endogenous volatiles [6; 12]. Many attempts have been made to improve the aroma quality of dry teas through optimization of processing methods and parameters [13; 14; 15]. Withering is an important step to release unwanted aroma compounds, such as green and grassy odor, and fruising is crucial to forming favorable fragrances such as floral scents [16; 17; 18]. Nevertheless, the chemical components of fresh tea leaves provide the material basis for forming the aroma of final dry teas. The tea cultivar is an important factor in the chemical composition of fresh tea leaves and the enzymatic activities of aroma volatile-related enzymes [11]. In China, there are hundreds of cultivars with their very own phenotypes and characteristic metabolite profiles. Some are suitable for processing green tea, and some are suitable for processing black tea or oolong tea. The scent type of tea is related to the volatile profiles of tea cultivars [11]. Moreover, the aromatic precursors and the activities of glycosidase enzymes that modulate the formation of odorants also vary with tea cultivars [11]. The floral aroma is associated with the value and quality of tea products. Under the same processing procedures, the dry tea prepared from tea cultivar 'Foshou' had a more intense floral aroma compared with 'Zhenong139' [16]. Tea cultivars suitable for processing oolong tea are usually characterized by floral fragrances, such as 'Jinguanyin', 'Tigeuanyin', and 'Jinmudan' [19; 20]. 'Chunyu2', a tea cultivar suitable for processing green tea, is also well-known for its orchid-like fragrance due to its genetic background. However, the respective contributions of cultivar and manufacturing procedure to the floral scent type of dry teas are still unclear, and the key odorants responsible for floral scent need further expatiation. Understanding the role of tea cultivar in the formation of the floral aroma of dry teas and the correlations of floral volatiles between fresh tea leaves and dry teas provides important guidance for tea breeding work. There are many factors associated with the scents of teas, and finding out the key factor is important to understanding the formation of characteristic features. The hypothesis of the present study is that the tea cultivar is the crucial factor in the formation of floral ascents of green and black teas, supplying the abundant floral odorants in the fresh leaves as raw materials. Here, green tea, black tea, and freeze-dried samples were produced from different tea cultivars, including 'Chunyu2' and 'Jinguanyin', which are associated with floral scents, as well as 'Chunyu1', 'Zhenong117', and 'Longjing43'.