Sandra SimpsonBumblebee petunia & plant genetics

Petunia Bumblee has proved popular with Kiwi gardeners – a black flower that has a yellow stripe on each petal – that although it has novelty value is an attractive plants in its own right. However, gardeners and garden centres have been disappointed and frustrated by flowers reverting to all black or being only partially striped. Zealandia Horticulture in Christchurch is the New Zealand agent for the plant and the company’s national sales co-ordinator, Aaron Blackmore, admits there has been a problem with “reversion”.

bumblebee petunia

“Under certain growing conditions a lack of yellow pigment can occur in the Bumblebee flowers, especially in spring,” Aaron says. He suggests the reasons for this are:
Plants propagated outside their normal growing season when temperatures and light levels are lower, meaning there can be a period of adjustment for the plants
Spring’s varying temperatures, i.e., warm one day, pouring with rain and 10 degrees cooler the next.

So what can be done to “correct” the plant?

bumblebee petunia“Remove the all-black flowers and you should find the next flush will have the yellow stripe in them,” Aaron says. “If they come through pure black again, repeat this process.
“The plant can be cut back, removing all flower buds and let to grow and revegetate forming new buds that will come through with the yellow stripe in them.”

The advice has been tested in international markets after Petunia Bumblebee, which was released internationally in 2011, displayed these same reversion problems in other countries.

“We are finding that people who have removed the initial flowers are now getting the distinct yellow stripe, and I have found my ones at home are now performing the way they should when early on they were pure black also,” Aaron says.

Sophia Frentz, a fourth-year genetics student at Otago University, offers a scientific explanation that backs up Aaron’s assertion that the problem may stem from forcing the flowers.

“It’s an example of epigenetics when flowers do things like revert. Flower colouring is ‘crazy genetics’ and we don’t really know what is going on. But the black would probably be the normal (wild?) colour while the yellow stripe would happen only under good conditions.

“This is thought to be because stripes, etc., act like landing stripes for pollinators, and if conditions don’t seem like they’ll be ideal for seed-making, why would you have landing stripes? Partially striped flowers are because cells divide, basically, so are when a mutation happens in one spot.”

Bumblebee petunia hidden genes illustration by Sophie Frentz

Bumblebee petunia hidden genes illustration by Sophia Frentz

If the climate is making the plant unhappy this can make genes hide (or ‘be hidden’, by proteins that “hang out” on DNA) and so they don’t get expressed, Sophia says. “That’s why if you plant flowers at the wrong time they might not have some stripes. And part-striping can occur if one half of the flower is by chance colder/more acidic/damper/unhappier than the other and so the gene that makes the stripe gets hidden.”

An alternative might be that transposons, which can jump around the genome, have messed it up. They don’t do it very much because they’re hidden (the same way the genes are).

Bumblebee petunia transposons illustration by Sophie Frentz

Bumblebee petunia transposons illustration by Sophia Frentz

“A lot of fancy flower things are made by making transposons jump into particular places (i.e., making them jump a lot and hoping): this funky-patterned corn is due to that.
“So if the yellow stripe is made by a jumping transposon then if the plant is unhappy with the climate it might make the transposon jump out/not function like it usually does.”

So that’s clear, then.

Sophia manages a cool science blog, SciCo (Science Community of Otago) that deals with anything of interest in the huge field that falls under the general heading “science”.

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Sandra Simpson

About Sandra Simpson

Sandra Simpson is a long-time journalist who in 2008 was asked to write a weekly garden feature for her local daily newspaper in Tauranga, New Zealand. Since then she’s visited beautiful gardens, met great people and attended several shows. In 2012 she started her own blog, Sandra’s Garden to share more of the people, places and events that make her corner of the world so bountiful.

6 thoughts on “Bumblebee petunia & plant genetics

  1. Jumping transposons sounds like something in the Star Wars bar. But what an interesting post Sandra. There are quite a few striped petunia flowers – like red on a white background. I wonder if they similarly sometimes refuse to show their stripes? Or maybe a dark colour like black will always hide a lighter colour more easily?

  2. Yes I agree – great post, really informative and makes me want to rush out and find some Bumblebees. I’d be just as happy with the all black flowers though. Of course it is possibly more to do with how the Tigers are going in the footy than genetics! I am often asked questions about flowers changing colour – agapanthus and iris in particular seem to do it – and usually becoming white instead of the original blue (ag) or yellow (iris). I think the agapanthus is more related to seedling variation, but I am wondering about the iris.

    • Hello Jennifer,

      I’ve been talking to Kiwi plant breeder Ian Duncalf about your comment that agapanthus flowers change colour – Ian released Agapanthus Thunderstorm, a miniature, late last year through Anthony Tesselaar Plants.

      He says agapanthus never revert, so the cause of the colour “change” is mostly likely to be a seed that has fallen into the crown of a plant and flowers before the plant proper, hence the “change” from white to blue (or vice-versa). Ian guarantees there will be two separate plants involved and says: “I’ve been caught like this myself and am now very thorough when I inspect ‘interesting’ plants”.

      Hope that’s some help to you (although sorry I don’t have anything to offer on the iris situation).

  3. What an interesting post, Sandra. Thank you. Fascinating the things that can interfere with genetics in plants. Probably ditto in humans.
    Love those black petunias. Rich and dark. Gorgeous.

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