Comparison of Biochemical Constituents and Contents in Floral Nectar of Castanea 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 (Castanea 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.

Keywords: Castanea; amino acid contents; nectar secretion; sugar content; volatile organic compounds.

Figure 1

Picture of a chestnut tree including shape of tree (A), male and female flowers (B,C). The secretion of nectar is mainly from male flowers [11], and it can be found that male flowers are much more abundant than female flowers.

Figure 2

(A) Total amount (μg/g) of VOCs and (B) relative content (%) of VOCs classes in floral nectar of Castanea spp. The different letters on the bars indicate significant differences among Castanea spp. based on One-way ANOVA with Duncan’s multiple range tests (p < 0.05). Each value represents the mean ± SEM (n = 3). Abbreviations; CCK, C. crenata (Korean cultivar ‘Mipung’); CCJ, C. crenata (Japanese cultivar ‘Ungi’); CDA, C. dentata (American chestnut); CMC, C. mollissima (Chinese chestnut); CSE, C. sativa (European chestnut).

Figure 3

Score (A) and loading (B) plot of volatile compounds according to Castanea spp. Abbreviations; CCK, C. crenata (Korean cultivar ‘Mipung’); CCJ, C. crenata (Japanese cultivar ‘Ungi’); CDA, C. dentata (American chestnut); CMC, C. mollissima (Chinese chestnut); CSE, C. sativa (European chestnut).