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Controlled pollination

Noelia Alvarez
4 November 2013

Our horticultural team is carrying out controlled pollinations in the Display Houses. Seed Collector Officer, Noelia Alvarez, from the Tropical Nursery Team explains how it is done and the reasons behind it.

Bags in the Palm House

Should you visit the wonderful Palm House conservatory at Kew (nice weather guaranteed all year around) you will come across some fabric bags hanging from some of the plants. Don’t worry, these are not early Christmas treats. These bags are part of a Seed Collection project carried out by horticulturists at Kew.

The living collections seed project

The project aims to bank seeds from the living collections held at RBG Kew. Priority is given to wild collected, conservation rated and historical specimens. The seeds are then safely stored in the Millennium Seed Bank at Wakehurst. This way we are safeguarding the collections for the future. It is a long-term insurance against the complete loss of the species and also provides a source of material for study of those species.

The bags are used to avoid cross pollination between closely related plants. This way the flowers which contain the reproductive organs of the plant are isolated from potential pollinators that transfer pollen in their search for rewards. The bags are made of very fine polyester (bridal veil) and they have been designed and made at Kew by volunteers skilled in this craft.

Hand pollinating

The next step is to hand pollinate the flowers inside the bags: this is the most fascinating part. There are so many plant families at Kew and understanding how the plant breeds in nature helps us with the pollination work. We have pollinated orchids, such as Gongora armeniaca, which in nature are pollinated by a group of bees called euglossine bees. The male bees collect the fragrant, oily compounds that the flowers secrete (these oils make them attractive to the female bees). It is an interesting symbiosis where the bees depend on the orchid fragrances they collect for their reproductive success and the orchids likewise depend on the euglossine bees for pollination.

We also pollinate plants which in their natural habitats are pollinated by geckos, for example Nesocodon mauritianus with its brightly red nectar - an attractive visual signal for lizards. And also plants pollinated by sunbirds like Aloe classenii - the birds tend to have long beaks adapted for extracting the copious nectar from the tubular flowers.

We use different tools to transfer the pollen from one flower to another, paint brushes (natural hair ones help with pollen adherence), tweezers, sewing pins, toothpicks, musical tuning forks, our fingers, and sometimes even our own hair.

Collection and storage

After pollination, if fertilization has been successful, a fruit is formed. The next step will be to collect the seeds at the optimum stage of their development when they are at their peak of maturity. This way the seed won’t lose viability when stored in the freezers at the Millennium Seed Bank. There are indicators of readiness for collection such as changes in fruit colour, fruits splitting, seeds rattling, changes of texture of the fruit wall, some seeds already dispersed, and so on.

Finally the seeds are collected into well-labelled cloth or paper bags which allow air flow and prevent mould formation and sent to the Seed Conservation Department at the Millennium Seed Bank where they are processed, tested and stored.

We have many examples of successful seed collections produced from our ex situ collections which are now safely stored at the Millennnium Seed Bank, for example:

  • Begonia salaziensis from Mauritius where the total population is recorded as being less than 50 individuals
  • Teline nervosa, endemic to the island of Gran Canaria (Canary Islands), where it is only present in two locations extremely threatened by exotic species, and urbanised areas

...and many, many more.

I expect the bags will be in the Palm House until the end of November, if not longer. We will be setting more bags in the Princess of Wales Conservatory and outside in the gardens from spring onwards.

Taking into account the large number of important living collections held at RBG Kew which we need to collect, you can expect to come across quite a few bags around the Gardens, each one helping us with the isolation and preservation of flowers around the garden.

- Noelia -

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