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”.
“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?
“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.”
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).
“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. http://waynesword.palomar.edu/images/transptr.gif
“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”. http://sciencecommunityotago.com/