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Evaluation of pollination and reproductive success in red clover (Trifolium pratense L.)

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

  • Shuxuan Jing
Seed production of red clover (Trifolium pratense L.) largely depends on bumble bees’ pollination. Compared to diploids, the lower seed yield of tetraploids limits the commercial exploitation despite a higher forage yield, persistence and disease resistance. Inadequate pollination was previously suggested as a reason for the low seed yield in tetraploids. However, pollination conditions are complex, making it difficult to compare the pollination between diploid and tetraploid red clover.

This study aimed to evaluate pollination and reproductive success in red clover using three pollination approaches: hand pollination, honey bee and bumble bee pollination. Pollination by hand and honey bees was used to investigate the optimal visitation rate and flowering stage to maximise reproductive success. Diploid and tetraploid red clover cultivars released from different years were used to explore the influence of breeding improvements. Pollinator performance among different bee species visiting diploids and tetraploids was investigated under field conditions. Collectively, the reproductive success between diploids and tetraploids was compared among different pollination approaches.

Results showed that pollination conditions were poorly described in previous studies and my review emphasised the importance of linking pollination and reproductive success. With the increase of “visitation rate” in hand pollination, the seed number per floret was reduced. Pollination at the full flowering stage obtained a higher seed number per floret than the early flowering stage. When comparing three pollination approaches, hand pollination in general obtained lower reproductive success than both honey bee and bumble bee pollination, depending on the pollen diversity. Furthermore, these findings emphasise the importance of multiple bee visits in order to maximise reproductive success. Bumble bee species of Bombus hortorum L. and Bombus pascuorum Scopoli were the dominant pollinators during the early flowering stage, whereas the latter was active throughout the flowering season. Stigmatic pollen deposition was found not different among pollinator species or plant ploidy levels. Visit frequency and visitation rate did not vary between the two ploidy levels but among bee species. However, relative abundance differed between diploids and tetraploids, probably related to corolla tube length. Compared to diploids, tetraploids had lower reproductive success in terms of seed set, pollen viability and pollen germination. Reproductive success of tetraploids seems improved with breeding over the past 50 years.

This study provides insights towards understanding the role of pollination in red clover reproductive success. Future research perspectives in terms of crop pollination management, pollinator conservation and plant breeding for seed crops were considered. To conclude, tetraploid red clover has lower reproductive success compared to diploid red clover, regardless of pollination approaches.
ForlagAarhus Universitet
Antal sider145
ISBN (Trykt)978-87-93148-94-9
StatusUdgivet - jun. 2021

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