Epsilon Archive for Student Projects

Abstract

Red clover (Trifolium Pratense L.) is an important crop grown for two purposes: it is a nutrient-rich fodder, and it is beneficial in crop rotations as nitrogen fixator. Sweden is a major producer of red clover seeds in Europe facing excessive seed yield fluctuations between 236 and 650 kg/ha. One of reasons of that is inadequate pollination as red clover is a cross-pollinated species. The most efficient pollinators of red clover are long-tongued bumblebees, but their populations are declining in Sweden. Floral scent is an important cue for bumblebees to locate flowers so ability of prolongated floral scent emission will increase chances of red clover to be pollinated.

The current study explored the composition and amounts of floral scent compounds in red clover inflorescences and differences between varieties. Two developmental stages of inflorescence were in focus: 1) late flower stage recognized as 100% open florets to 5 wilted florets and 2) end of pre early senescence stage recognized as the latest possible day until 50% wilted florets. Late flower stage was perceived as a possible period of the highest floral scent emission while the end of pre-early stage represented a possible situation in future when flowers would have to wait longer for pollinators. All flower heads were kept bagged since the bud stage to exclude pollinators.

Acetophenone and (E)-ocimene were identified as the main components of red clover's floral scent. Remarkably, ageing flower heads from all varieties continued to produce scent 7-12 days after entering the late flower stage, even with up to 50% wilted florets. The average scent emission levels from these ageing flower heads were significantly higher than those from recently opened ones. Varieties differed in their aging rates and floral scent emissions. It appears that the tetraploid variety Betty wilted more quickly and produced less floral scent than other varieties, while the diploid variety Yngve had the longest late flower and pre early senescence stages and the highest floral scent emission. The findings of this study could help identify promising genes for future breeding, aiming to develop the tetraploid varieties that are both high in biomass and seed yield.