Wetenschap - 10 oktober 2013

Bumblebee protects spuds

Roelof Kleis

Isn’t it every scientist’s dream? To be engrossed in your research when something strikes you as remarkable. An oddity in the margins of your field of study. You could call it an added bonus. Serendipity. In searching for A, you find B, which is something much more important. This is pretty much to what happened to Albert Corporaal, an ecologist at Alterra.

Corporaal is fascinated by fritillaries. He has been studying them for years. Why is this fritillary pollinated by bumblebees and that one not? Corporaal discovered what was driving their choosiness: UV light. In ultraviolet light bumblebees see exactly where to go to get the best nectar. But he was struck by something else. Pollinated fritillaries are fitter than the rest. They are less likely to succumb to the soilborne fungus Pythium. How is that possible?, he wondered. And then the bumblebee entered the picture. Corporaal set up a series of tests that established indisputably that somehow or other the plant’s protection is due to the bumblebee. A real find. And he went further. After all, why should this talent apply only to the fritillary? ‘Is there an organism that has a similar systemic relationship with bumblebees? Could I think of a plant with a similar bulb or tuber system, a plant moreover that is troubled by a related fungus?’

Corporaal soon came up with the potato and its biggest threat: Phytophthora, the notorious potato blight. ‘Potatoes the world over are sprayed more heavily than any other food crop. Half of all fungicide use is directed at Phytophthora. Imagine for a moment that bumblebees could protect potatoes.’ Together with fellow biologist Anton Stortelder, Corporaal set to work with a sack of fertile Bildstar seed potatoes. Notice the word ‘fertile’ in the preceding sentence. For this trick to work, the potato has to be capable of being pollinated.

And right there is the reason why the potatoes we put on our plates can’t be helped by the bumblebee. We eat varieties that are infertile, that have no flowers. Flowers come at the expense of the potato. The plant mustn’t expend its energy on flowers. Corporaal set out two cages covered in bee-proof netting, each measuring 5 by 5 metres and containing a hundred plants. One with bumblebees and one without. A third field, open and thus exposed to the natural (insect) environment, served as a control. The results were abundantly clear. ‘Above ground the difference was 100 percent. Underground only two plants were infected with Phytophthora in the bumblebee cage, compared with ten times that number in the other cage. What’s more, in the cage without bumblebees 90 percent of the plants were troubled by click beetles, which drill holes in the potatoes, making them unfit for sale.’

New variety
How does the bumblebee do this? Corporaal thinks it is a question of hormones. ‘Fritillaries that are pollinated live a month longer than the others. That month is crucial to the formation of berries. When the bumblebee pollinates the flower, something changes in the flower’s chemistry. A chemical signal is released that says, “Stay alive, we still have a month to go.”’ Evidently, this signal also ensures that the plant’s defence against disease remains intact. However it works, it really does. And, in all likelihood, not only for fritillaries and potato plants.

Corporaal thinks that this relationship between plant and pollinator is at work in some 40 food crops worldwide. The protection provided by bumblebees works only for fertile crops. So to get natural protection we need to start developing entirely different varieties. In other words: away with the infertile spud . ‘I think so,’ says Corporaal. ‘We will have to seek varieties that both appeal to bumblebees and are high-yielding. This should not be too difficult. Worldwide, I believe, there have been no fewer than 2000 different varieties of potato. It has taken us a hundred years to develop today’s potato. So using current techniques, we should be able to find an appropriate potato within ten years.’ This creates a win-win situation. A spud like this with natural protection is good for the world’s food problems since it removes the need for expensive chemical protection. And it is good for the landscape too since pollinators like the bumblebee and the honeybee thrive in small-scale flora-rich landscapes with embankments, canals, verges and the sides of ditches.

Photo; Adriaan Holsappel