Abstract
Volatiles from flowers at three blooming stages of nine citrus cultivars were analyzed by headspace-solid phase microextraction (HS-SPME)-GC-MS. Up to 110 volatiles were detected, with 42 tentatively identified from citrus flowers for the first time. Highest amounts of volatiles were present in fully opened flowers of most citrus, except for pomelos. All cultivars were characterized by a high percentage of either oxygenated monoterpenes or monoterpene hydrocarbons, and the presence of a high percentage of nitrogen containing compounds was also observed. Flower volatiles varied qualitatively and quantitatively among citrus types during blooming. Limonene was the most abundant flower volatile only in citrons; α-citral and β-citral ranked 2nd and 3rd only for Bergamot, and unopened flowers of Ponkan had a higher amount of linalool and β-pinene while much lower amount of γ-terpinene and p-cymene than Satsuma. Taking the average of all cultivars, linalool and limonene were the top two volatiles for all blooming stages; β-pinene ranked 3rd in unopened flowers, while indole ranked 3rd for half opened and fully opened flower volatiles. As flowers bloomed, methyl anthranilate increased while 2-hexenal and p-cymene decreased. In some cases, a volatile could be high in both unopened and fully opened flowers but low in half opened ones. Through multivariate analysis, the nine citrus cultivars were clustered into three groups, consistent with the three true citrus types. Furthermore, an influence of blooming stages on clustering was observed, especially with hybrids Satsuma and Huyou. Altogether, it was suggested that flower volatiles can be suitable markers for revealing the genetic relationships between citrus cultivars but the same blooming stage needs to be strictly controlled.
Highlights
Floral fragrance has been studied over the last decade to understand the biosynthesis, emission, regulation and ecological impacts of emitted floral volatiles [1]
The amount of some volatiles, such as linalool in Huyou, γ-terpinene in Yuhuanyou, α-citral in Ponkan and Liubencheng, as well as β-elemene and (E)-ocimene in Qingjia, was high in both unopened and fully opened flowers but was low in half opened ones (Figure 3). These results provide clear evidence that the content of some major volatiles did not consistently increase during flower blooming, and that volatiles have a great influence during flower maturity, probably related to their different roles during development such as protection against pathogen and attraction of pollinating agent [27]
The profiling of flower volatiles from nine citrus cultivars at three blooming stages revealed significant differences between cultivars and blooming stages
Summary
Floral fragrance has been studied over the last decade to understand the biosynthesis, emission, regulation and ecological impacts of emitted floral volatiles [1]. Flower volatiles play important roles in communication between flowering plants and their pollinating agents [2,3], and repelling of herbivores [4,5]. Flower volatiles are important due to their commercial application in food, pharmaceutical, perfume, and cosmetic industries [6,7]. Terpenoids are the largest class of plant secondary metabolites, having many volatile representatives, and are important components of floral scent in a wide range of species [10]. They represent the largest and most diverse family of natural products, including over 30,000 individual compounds, half of which can be synthesized by plants [11]
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