Objective To investigate the composition content and structure of carotenoids in yellow flower of native Dendrobium species and their biosynthesis pathways, thus proving references for further investigation of the floral pigment mechanism and molecular breeding of Dendrobium.

Method The flower color in yellow petals and labellum of Den. chrysotoxum, Den. densiflorum and Den. thyrsiflorum were observed according to the Royal Horticultural Society Color Card (RHSCC). Besides, the carotenoids in the petals and labellum in 3 Dendrobium species at full opening stages were determined using UPC²-MS/MS. Based on the results of UPC²-MS/MS, the biosynthesis pathways of carotenoids in Dendrobium were proposed.

Result The result indicated that the floral color of the 3 Dendrobium species could be divided into white group and pale yellow-yellow-golden yellow group. Totally, 8 kinds of carotenoids were detected from the petals and labellum in the 3 Dendrobium species, respectively, including β-carotene, α-cryptoxanthin, β-cryptoxanthin, violaxanthin, lutein, antheraxanthin, zeaxanthin and lutein-5, 6-epoxide. According to the results of quantitative analysis, white petals of Den. thyrsiflorum contained the lowest carotenoids (52.26 μg·g^-1). The content of carotenoid increased with the enhancement of yellow color and the carotenoid compounds in the golden yellow labellum of Den. thyrsiflorum was the highest, reaching 3 810.89 μg·g^-1. Among 3 carotenoids contained cultivars, the lutein was majorly contained in pale yellow petals of Den. thyrsiflorum, while golden yellow labellum of Den. densiflorum and Den. thyrsiflorum majorly contained α-cryptoxanthin, lutein and lutein-5, 6-epoxide. Yellow petals of Den. chrysotoxum contained violaxanthin, lutein and antheraxanthin.

Conclusion The carotenoids in pale yellow and golden yellow petals are mainly α-carotene and its derivatives, while that in bright yellow petals are mainly β-carotene and its derivatives. Regulation of the LCYE genes which may cause carotenoid biosynthesis will result in flower color change in yellow flower of Dendrobium.