How to prevent thornless berries reverting to thorny

Thornlessness in brambleberries appears to be influenced by at least three different factors.  Scientists and plant breeders have understood these factors reasonably well for quite some time.  Each of them has different advantages and disadvantages.   But how do you keep a thornless berry thornless, and how do you prevent a brambleberry from reverting to being thorny?

First, let me tell you about my experience growing a "thornless youngberry", then let me explain the three different ways that brambleberries can be thornless, then I will explain what you do about each of the three types.

Thornless youngberry starting to ripen

In blackberries, raspberries and their many hybrids the ‘thorns’ are botanically known as ‘prickles’, but most people refer to these prickles as ‘thorns’ and most people refer to the lack of prickles as ‘thornless’, so to reduce confusion that is what I will refer to them as for here on.

The youngberry was still completely thornless in this picture

My thornless youngberry
I wanted to get a boysenberry.  I don’t have a lot of space, and pruning/disposing of thorny canes in town is problematic, so I prefer thornless plants.   Youngberries taste amazing, they are like a boysenberry but the berries are slightly smaller, darker, and they crop a few weeks earlier and more prolifically.   I would prefer a boysenberry, but could not find a thornless boysenberry for sale in Australia, so I paid more and got what was described as a "thornless" youngberry.

The dormant plant that arrived was indeed thornless and did appear to be a youngberry.   As it sent up new canes they were all completely thornless.   As the canes grew longer, some of the higher leaves started to get little hairs on the backs where the thorns would have been on a thorny plant.   The lower canes and leaves were still entirely thornless.   I was concerned that this may have been reverting to thorny so I sent an email to the company (New Gippsland Seeds) and asked about this, they never replied. Very poor form New Gippsland Seeds, very poor form indeed!

As the canes grew longer the hairs got thicker and longer and more numerous the further from the roots they were, these thicker hairs started to get curved and look like soft thorns.  These hairs were on the backs of leaves and started to appear along the cane itself.   I was more worried so sent another email to New Gippsland Seeds and asked about this, but was ignored again.  No reply whatsoever. Poor customer service New Gippsland Seeds, I am not impressed.

Eventually the parts of the cane furthest from the roots had large thorns, while lower down on the same cane the plant was completely thornless.  I was confused, I had a pretty good understanding of two of the three factors that influence thornlessness in brambleberries, and this did not fit with either of these explanations.   Then I learned of a third thing that can influence thornlessness in brambleberries.   Unfortunately this third factor appears to fit with my plant.  I emailed New Gippsland Seeds to ask about this, but they have not replied.  This is dreadful service, it isn't difficult to reply to my emails.

It is the fact that New Gippsland Seeds knowingly sell thornless plants that they know will revert to thorny, plus the fact that the company keeps ignoring my emails and won’t send any form of response, that defines this company.  This is the reason that I will not buy from them again.   I also think that with this kind of deception and poor customer service that you should also refuse to buy from New Gippsland Seeds.

Thornless berry flowering

Three factors that influence thornlessness in brambleberries

The first and simplest to understand is genetic thornlessness, in which the entire plant will be thornless no matter what as it lacks the genes required to produce prickles.   These plants will lack epidermal hairs and cuttings taken from them will always remain thornless.   Breeding new varieties of genetically thornless plants can take time due to the often recessive nature of thornless genes and the polyploid nature of many brambles so there are very few varieties of these in existence.  Genetically thornless are the ideal thornless plants as they can never revert to being thorny. You don’t need to prevent these from reverting to thorny as they can’t grow thorns.

The second group are thornless periclinal chimeras.  Plants are made up of several layers of tissues, sometimes each layer will contain slightly different genes.  Only the epidermal layer of tissue is genetically thornless in periclinal chimeras and all the other layers carry genes for thorns.  Only the epidermis is capable of growing prickles, as long as the other layers are not exposed the plant will remain thornless.  These plants can revert to thorny states easily enough, if a root gets damaged by an insect or growing past a rock and sends up a cane it is probable that one of the other layers will be on the outside, that part of the plant will likely be thorny from then on.   Sometimes a cane will get damaged in some other way and it will grow thorns from that point on.  Any part that reverts to thorny will not grow thornless again, so it is best to remove any thorny canes if you see them.   Some can revert to thorny quickly, others take many years, and some apparently stay thornless for a very very long time.  To prevent periclinal chimeras from reverting you need to remove any thorny canes, try to prevent any root damage from stones or insects, and hope for the best.  Thornless periclinal chimeras are not ideal, over a long enough timeline or without putting in work they generally revert to thorny phenotypes.

The third type is hormonally induced thornlessness.   I have only learned of this recently and have a basic understanding of how it works.  I hate that this third type exists and feel like the people who knowingly sell these are dishonest.  I believe that this is what happened with my thornless youngberry!   In this type of thornlessness the plant is treated with hormones, it then stops growing thorns for some time while this hormone is present in the correct concentration.  This hormone eventually wears off as the plant grows and the plant slowly reverts to being thorny.  Once that happens you are left with a thorny plant.  This sounds exactly like what happened with my youngberry.   I don’t see any reason these exist other than to trick people into buying something that is different from what was described.  You can’t prevent these from reverting, it is just a matter of time and the clock started ticking before you even thought about ordering your so called thornless berry plant.

Thornless youngberries and thornless blackberries, they have grown huge since this photo

To summarise how to prevent thornless berries from reverting to thorny:

1. You don’t need to do anything if the plant is genetically thornless as it can’t and won't produce thorns;
2. You should remove any thorny parts of periclinal chimeras, try not to damage the roots, hope for the best; and 
3. You can’t do anything if it is hormonally induced as it will wear off and produce thorns sooner or later.

Where to buy thornless berries in Australia
Don't EVER buy seeds of thornless plants from ebay, you could get sent seeds of anything and won't know until it is far too late.  I wouldn't buy 'thornless' berries from New Gippsland Seeds as it appears that the ones they sell are hormonal induced and will revert pretty quickly.  I am not sure if this is just the youngberry or if it is all of their so-called thornless berries, they won't respond to any of my emails so I can't know for sure, which is why it is best to avoid buying from them.

Over winter I sell some raspberries including some that are thorny, some thornless, some primocane, some floricane, and some yellow fruited for sale.  The thornless raspberries are genetically thornless.  I may sell blackberries and other berries at some stage and I will be clear if they are thornless what type of thornlessness they carry.  Everything I have is listed on my for sale page.