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Case study of crop pollination – Courgettes

Dr Jessica Knapp talks to us about the pollination of courgettes.
My name is Dr. Jessica Knapp and I’m a pollination biologist, and my research has looked at pollination of courgette crops. So courgette is dependent on pollination for its fruits and they’re actually pollinated by two key bee species One bumblebee species and a honey bee species. Courgettes are grown globally and in other parts of the world there’s some other really important pollinators for these crops.
So the squash bee for example, which is native to North America is an important pollinator too This courgette field that we’re in now is part of a farm which produces nearly a third of the courgettes in the United Kingdom and the pollination levels here in this farm are really good and there’s really no yield deficit and that means that the plants are producing pretty much maximal yields which is really good and the reason for that is because there’s lots of natural habitats surrounding these fields which are offering the bees really important food resources which are boosting their populations and allowing them to pollinate the courgettes So although pollination is important for courgette fruit set, courgette can actually produce some fruit without pollination all together and that’s around 56% that’s by a process known as parthenocarpy which is fruit set in the absence of fertilization and this trait is really important in the growing industry because some plants have being selectively bred for this trait say for example the Cavendish banana because the need for pollination is removed because the plants can produce their fruit without any fertilization and it means that growers are able to produce fruits in countries that would otherwise be adverse to pollinators and a further advantage of this as well as that the fruit will be seedless

Dr Jessica Knapp talks to us about the pollination of courgettes.

Plants in the Cucurbitaceae family provide a good example of crops benefiting from insect pollination. This diverse plant family includes fruit widely available today in our supermarkets such as melons, cucumbers, squashes and the courgette or ‘zucchini’. The flowers have hundreds of ovules which must be pollinated to produce the large fruits which contain hundreds of seeds. In their native range, cucurbits are visited by a variety of bee species, and the ‘squash bees’ are specialist on these crops and very effective pollinators.

When these crops are grown outside their native range, for example courgettes in the UK, then the local pollinator population need to do the job. To confirm whether pollination is being carried out successfully, we can compare the yields of flowers that have been hand pollinated or exposed to pollinators, with those that have not (flowers protected with mesh bags).

We then test whether there is a pollinator deficit i.e. whether the local population of pollinators are pollinating the crop for maximal yield. The difference between these two yields demonstrates whether there is a pollination deficit that could be reduced by increasing the number of pollinators in the field artificially (by introducing bees for instance).

For courgettes in the UK, our group found that the flowers could set fruit without any pollination at all, but insect pollinators increased courgette yield by 39%, and there was only a 3% pollination deficit, suggesting the local pollinator populations (mostly bumblebees) were doing a really good job!

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