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Breeding better beans for bees

Bombus pascorum tripping a bean flower. Photos by EB

This week I am very excited to have reached a big milestone in my scientific career: the publication of the first of my PhD research papers (Available open access at:! The research published forms part of a larger project I undertook at Cambridge University in Beverley Glover's lab, looking at how to optimise the flowers of the field bean (Vicia faba, also known as the broad bean) to increase bee visitation rates.

Pollinators and food production

Pollinators, especially wild bees, are extremely important for global food production. Over 70% of the most important crops worldwide have yields that are pollinator-dependent, ie. animal pollinators increase their yield compared with when no pollinators are available. The field bean is one example of a pollinator-dependent crop. Bee visitation can increase yield by as much as 50%. It has also been shown that bees are even more important in recovering yield after heat waves, an event that will become more frequent with climate change. In fact, growers of the field bean have commented on how the yield of the field bean has become increasingly variable over the past few years, which could be linked to declines in bee populations or changes in the climate over recent years.

​​Breeding for optimised flowers

Bumblebee visiting field bean flowers. Photo by EB.

​​When I began my PhD, I wanted to both work on pollinators and have an applied aspect to my research. Previous breeding efforts in the field bean have focused on traits such as disease resistance and nutritional value of the seeds for consumption by humans and livestock. In the process of breeding for these traits, plants with flowers that were less suitable for bees may have been selected. Flower traits such as nectar production or flower colour are extremely important in determining if/which pollinators visit a flower. Therefore, suboptimal flowers can decrease visitation rates and reduce crop pollination. Thus, for my PhD project I decided to investigate if flowers could be bred to improve visitation rates by bees to the field bean. If so, this could result in higher and more stable yields.

​​The reward of field bean flowers

One of the genetic lines that we investigated. Photo by EB.

​​In my latest paper we asked 1) how rewarding the flowers of the field bean were and 2) whether there was genetic variation in their reward? Genetic variation is important because it means we can breed flowers with a desired reward value? To do this we grew several plants each of 30 different genetic lines of beans. Beans were grown in glasshouse under controlled conditions, minimizing environmental variation. From these plants we took multiple measurements of flower traits that are known to affect bee visitation, including colour, size, shape, and pollen/nectar production. This was a substantial undertaking! The final dataset included measurements of the amount of nectar produced by 1874 flowers (I couldn’t have managed this without help from fellow PhD student Jonathan Pattrick), and pollen production from 172 plants. In the paper published today we show that there are substantial differences in the amount of pollen and nectar produced by different plant lines. These differences are the result of genetic differences between plants. One trait we believe could be particularly useful for improving visitation rates is optimizing the sugar concentration of nectar. Using bumblebees in the lab we showed that ~ 55 % sugar in nectar (by weight) is preferred by bees - compromise between the viscosity (not too treacley and hard to drink) and sugar content of the nectar. One of my favourite parts of this work was from a much smaller experiment though: two lines for which we measured the force required to open flowers using a contraption designed by Silvina Córdoba & Andrea Coccuci. We found that the force required to open flowers was roughly 1/10th of the force a bumblebee can exert on a flower, but could be a problem for weaker honey bee individuals or solitary bees, and is definitely worth investigating further!

Bean pods. Photo by EB.

Next steps

​The next big step for this work is to take plants with traits that will be preferable to bees (eg. a high nectar concentration) and see how their yield compared to plants with less favourable flowers in the field. There is also the potential to breed crops with a higher reward value (irrespective of its effect on yield) to increase forage for bees in agricultural land: if you are going to grow a crop its better to grow one that will be better for pollinators! This strategy will of course need to be combined with wild flower strips to prolong forage availability across the season, but could be highly beneficial.

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