Cymbidium kanran can deceptively attract Apis cerana for free pollination by releasing specialized volatile compounds

Abstract

Cymbidium kanran is classified as a second-level protected plant in China and is also listed in the World Genetic Conservation Plant Registry. Pollen flow is an important factor influencing the genetic structure of plant populations, holding significant relevance in the conservation of endangered plants. In this study, we present a comprehensive exploration of the pollination biology of Cymbidium kanran, encompassing investigations into its flowering phenology, breeding system, floral volatile components, and interactions with pollinating insects. The results showed that: 1) C. kanran exclusively relies on external pollination mechanisms, as automatic self-pollination or apomixis mechanisms are conspicuously absent. Consequently, the natural fruit set rate is significantly lower compared to artificial pollination, highlighting a pronounced pollination limitation. 2) Apis cerana emerges as the primary effective pollinating insect for C. kanran, adeptly carrying both pollinia and anther caps during the pollination process. Notably, C. kanran does not provide any rewards, such as nectar or edible pollen, to entice the pollinators. 3) Contrary to expectations, our glass cylinder experiment demonstrates that the flower color of C. kanran lacks significant attractiveness to pollinators (p=0.1341>0.05). However, the scent emitted by the flowers exhibits considerable allure (p=0.0004<0.05), despite C. kanran boasting one of the most diverse color variations within the Cymbidium genus. 4) Based on dynamic fluctuations in floral volatile components during different flowering stages, we hypothesize that hexanal, heptanal, octanal, 2-pentyl furan, 4-methyl-2-pentanone, and 1,4-cyclooctadiene may serve as pivotal volatile compounds responsible for attracting pollinators. This study establishes a robust scientific foundation for the conservation efforts concerning C. kanran, thereby facilitating the sustainable management and protection of its wild resources.