Some plant genetics

Sophia Frentz, in her Honours year of a science degree with a major in genetics, has been in touch regarding the posting on the reversion of Petunia Bumblee to an all-black flower (instead of sporting yellow stripes on the petals). She writes:

“It’s an example of epigenetics when flowers do things like that. 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.

“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. 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.


Illustration: Sophia Frentz

“Or … transposons are things that can jump around the genome and mess it up. They don’t do it very much because they’re hidden (the same way the genes are). 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 unhappy climate might make it jump out/not function like it usually does.”


Illustration: Sophia Frentz

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”.

Petunia reversion

Some gardeners have been experiencing problems with Petunia Bumblee not doing what it says on the packet – a yellow stripe on each petal – and instead having partially striped flowers or all black flowers.

bumblebee petunia - Copy

Partially striped and black flowers on Petunia Bumblebee. Photo: Sandra Simpson

Zealandia Horticulture in Christchurch is the New Zealand agent for the plant and the company’s national sales co-ordinator, Aaron Blackmore, sent this email about the problem:

We have been experiencing some reversion with the flowers on the new Bumblebee petunia – this has meant that the initial flowers are coming out pure black. Under certain growing conditions a lack of yellow pigment can occur in the Bumblebee flowers especially in spring.

Reasons for this occurrence:

  • These plants have been propagated outsideĀ their normal growing season when temperatures and light levels are lower, meaning their can be a period of adjustment for the plants
  • Climatic variations which can be quite prevalent in early spring, i.e., warm weather one day, pouring with rain and 10 degrees cooler the next.

What can you do if this occurs?

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

These plants were first released in the international marketplace last year with similar reversion occurring. The advice given by the retailers and breeders in these markets is as above.

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