# Comparison of Biochemical Constituents and Contents in Floral Next of _Castanae_ spp.
###### Abstract  
Pollination is essential for efficient reproduction in pollinator-dependent crops that rely on the attraction of pollinators to flowers. Especially, floral nectar is considered to be an important factor attracting pollinator like honey bees, but differences among major chestnut species (_Castanae crenata_, _C. mollissima_, _C. dentata_, and _C. sativa_) are still little explored. This study aims to evaluate the value of honey source by analyzing floral nectar characteristics and comparing the composition of volatile organic compounds (VOCs) that mediate plant-pollinator interaction. In this study, we analyzed nectar samples obtained from male flowers using HPLC and HS-SPME/GC-MS. The five chestnuts showed significant differences between the volume of secreted nectar, free sugar composition, amino acid content and VOCs composition. Furthermore, _C. crenata_ (Japanese cultivar 'Ungi') was revealed to emit the highest total amounts of VOCs and high levels of benzenoid compounds that are generally associated with flower-visiting insects. The sugar content per catkin, which is used to determine the honey yield, was the highest in _C. crenata_, suggesting that _C. crenata_ 'Ungi' can be highly valued as a honey tree. Therefore, a better understanding of the relationship between pollinator and nectar characteristics of _C. crenara_ could contribute to a prospective honey plant. C 2020254225  
Castanea (Chestnut), belonging to the family Fagaceae, is distributed in over ten species in temperate climate regions, including Asia, Europe and North America. Among chestnut trees, _C. crenata, C. dentata, C. sativa_, and _C. mollissima_ are important species consumed as a crop. In Korea, a chestnut pest (_Dryocosmus kuriphilus_) infection occurred in 1958, putting chestnut trees on the verge of extinction. To overcome the decline of the chestnut tree population, various chestnut tree species were introduced in 1965 from Japan, China, North America, and Europe to improve insect-resistance and fruit production. Currently, chestnut trees are distributed over about 77,440 ha and account for 21.3% of major non-timber products in Korea [9; 10]. Chestnut trees are valuable not only as a food, but also as a honey source plant, being already classified as major honey plants in many countries [11]. The inflorescence is composed either of male or female flowers, or staminate and pistillate flowers occur together. Only the male flowers produce nectar that is secreted on the surface of the disc located at the base of filaments in staminate flowers (Figure 1), from which is possible to produce 27.2 kg of honey per 100 trees [11]. Chestnut honey was also identified to contain functional and specific substances: The content of kynure acid which shows anti-inflammatory and anti-oxidant effects was high in _C. sativa_ honey [12]. Additionally, 1-phenylethanol and 2-aminoacetophenone are considered marker compounds of unifloral chestnut honey [13; 14]. Volatile organic compounds (VOCs) that mediate plant-pollinator interaction has been evolved by pollinator behavior for reproductive success [15], and the VOCs of the chestnut flower have been reported in several studies to date [16; 17; 18]. Even though floral nectar is considered to be an important factor attracting pollinators like honeybees, little is known about pollinator attractant factors in major chestnut species yet. Hence, this study aims to evaluate the value of honey source by analyzing floral nectar characteristics, as well as comparing the composition of VOCs. We collected floral nectar in _Castanea_ spp., such as _C. crenata_ (Korean cultivar 'Mipung', CCK; Japanese cultivar 'Ungi', CCJ), _C. dentata_ (America sweet chestnut, CDA), _C. mollissima_ (Chinese chestnut, CMC), and _C. sativa_ (European chestnut, CSE), from extension forest in National Institute of Forest Science (Suwon, Republic of Korea) that were planted in 1995. Our work could contribute to a comprehensive understanding about breeding for high-quality and increasing honey production within chestnut trees.