Pollination system and hybridisation of Tabernanthe iboga: successful crossing of two forms with different fruit morphology.
Tabernanthe iboga (family Apocynaceae) is native to Western Africa; Angola, Cabinda, Cameroon, Central African Republic,…
Plant mutation breeding applies to the use of either chemical mutagens (colchicine, oryzalin, etc) or ionising radiation (gamma or x-ray) to induce mutations (both beneficial and also deleterious) in seeds or other propagation material such as budwood or seedlings. The aim of mutation breeding is to rapidly acquire beneficial changes in the genome, changes in ploidy (polyploidy, increasing the number of chromosomes), increased alkaloid content, plant vigour, plant height, dwarfing, biomass yield, or seedless varieties in Citrus for example. Compared with acclimatisation, hybridisation or selection, mutation breeding can bring about rapid, as well as interesting, changes to the target species. Mutagenesis does not always occur easily, or can greatly affect a particular species. The amount of radiation, measured in grays (Gy), required to induce mutagenesis varies greatly. One gray (Gy) is the international system of units (SI) equivalent of 100 rads, which is equal to an absorbed dose of 1 Joule/kilogram. An absorbed dose of 0.01 Gy means that 1 gram of material absorbed 100 ergs of energy (an erg is one-ten-millionth of a joule) from NRC.gov. High doses of gamma radiation can have negative effects on different vital processes and growth characters with different species. Getting the dose right takes some experimentation and research into previous papers.
Trichocereus are very popular cacti among collectors and enthusiasts, for their horticultural and medicinal potential. I couldn’t find any particular studies or papers focusing on the mutation breeding of Trichocereus, so I thought this was a worthy project to look into. Many years ago my ex-partner and I used oryzalin to try and induce polyploidy in a few species, some of these were Trichocereus seedlings. Several survived and over the years they became mixed in with my collection and I lost track on them. I still think I know which ones they are and would like to get them tested one day to see if any changes occurred.
Thinking about using chemicals again for mutagenesis wasn’t appealing to me, so I looked into gamma irradiation, which can have good results and is less dangerous for the breeder. Working out doses to use was guesswork at best, but after researching papers I settled on three treatments for the seeds and three for small (2.5cm tall) seedlings. For the trials I used several lots of hybrid seeds and seedlings, which included HB02 x HB01 seeds and HB07 (open pollinated ‘OP’) seedlings. I also treated a T. peruvianus ‘Huarimayo monstrose‘ reverted cutting. Seeds were treated at 100, 150 and 200gGy. Seedlings (being more susceptible to radiation) were treated at 20, 40 and 60Gy. The material was sent way to a research facility for treatment. I potted the seedlings up on arrival back here and sowed the treated seeds as per normal, using the takeaway tek.
For the seeds it was clear that all of these doses were most likely too small. Normally you would look for reduced viability with increased radiation exposure. Seeds are more highly resistant to the effects of gamma irradiation, compared to seedlings. I can detect no observable changes in expression of the genome of seedlings grown from gamma treated seeds at these levels (so far). For further experiments with Trichocereus seeds, I would look at 250, 350, 450, 550 and up to 1000Gy treatments to work out the best dose.
The Trichocereus ‘HB07 OP‘ seedlings were a better success story. Many died and I am now left with 7 cacti that are growing very well, after initially struggling. None survived the 60Gy treatment, and only one survived the 40Gy treatment. All the rest were 20Gy treated. I would suggest further experiments using 20-40Gy doses. The roots are particularly affected by the radiation and it may be better to use small (~10cm) tip cuttings to avoid this, which displays as die off of the roots. It would also be advantageous to use the same clone so that you can observe changes more easily. The Huarimayo developed a patch of variegation after being treated, pictured below.
After a few set backs and slow growth rates initially, all seven cacti are now growing very well. In the coming years I will be reducing the number of cacti in my collection to focus on a smaller number of elite lines that show advantageous growth in our subtropical climate, better disease resistance, and are of more use medicinally in the future as the benefits of psychoactive plants are scientifically validated and utilised in modern medicine applications. These gamma irradiated Trichocereus will become a new line I will multiply, under the names HBG1 – HBG7 (if they perform well and survive!).
I hope this encourages further experimentation with plant mutation breeding among Trichocereus cacti and other psychoactive plant species, as a viable method to induce beneficial changes. Feel free to get in touch or leave a comment if you have a question.