In its long journey of Darwinian evolution, starting from an unknown and ancient progenitor, nature has been able to create, through the mysterious phylogenetic paths of speciation, the more than 600 of Passiflora currently living. Many have certainly become extinct, both due to natural phenomena and to the damage that man has produced and continues to produce to the environment.
I often wonder how it could be that it was this passiflora zero that gave rise to a large phylogenetic tree. Only a fortunate discovery of paleobotany could give us an image. I am curious and fascinated by it. However, we too can be small creators without having to wait the millions of years of evolution and without having to resort to genetic engineering. Thanks to hybridisation we can obtain new plants that have never existed before.
Currently there are about one thousand artificial hybrids, almost all created by man, with rare exceptions of natural hybrids which can be seen in this Hybrid Registry
The Passiflora flower lends itself very well to being used to obtain new varieties, as its reproductive structure is evident and easily accessible. Any one of us is able to fertilise a flower of one species or hybrid with the pollen of another passiflora.
I will explain my technique below.
The male genetic material is contained in the pollen grains, while that of the female is contained in the eggs present in the ovary. Both gametes possess half of the chromosomes present in the other cells of the plant; by adding together the chromosomes of the pollen and those of the egg cell, the complete genetic code is reconstituted; it will be present in the embryo contained in the seed and therefore in the new plant.
I have simplified, of course. This process occurs in most living beings that have sexual reproduction.
To obtain a hybrid it is necessary to deposit on the stigma of Passiflora A the pollen brought by the anthers of Passiflora B. The pollen deposited on the stigma and stimulated by the hormones of the same, wakes up and, through the stylus, introduces the pollen tubule containing its half of the genetic material genetic up to the ovary where it meets the egg with the other half and completes it. The seed containing the embryo formed by cotyledons, radicle, hypocotyl and endosperm will then form, enclosed in the integument which, once mature, will germinate to produce a new plant.
Following hybridisation, this new specimen will have characteristics that are different from those of the parents, unpredictable and, in many cross-breeds, really surprising.
It should be noted that not all passifloras are compatible with each other. There are species/hybrids that function as pollen acceptors and other are refractory. The same goes for pollen which works with some, while on others not. It is difficult to obtain hybrids between plants belonging to different subgenera, and even within the same subgenus there are incompatibilities.
Let us now take a look at the practical part.
When I am lucky enough to have two different flowering passifloras and I want to try to hybridise them, I just choose the mother plant (A) and the father plant (B) from among compatible species. Sometimes I also try reciprocal cross-breedings.
The choice depends on a number of
considerations. First of all, the flower of the father plant must have pollen
and that of the mother plant must have a well-formed gynoecium free from
I remove the anthers from the flower of the mother plant (A), immediately in the morning, before pollen has formed, to avoid self-pollination. I remove the five anthers when they have pollen from the flower of the father plant (B).
With simple tweezers I rub the anthers (B) on the stigmas of the mother plant (A) until the pollen is deposited. At this point, the stigmas of the passiflora are covered in pollen and there you have it.
I do not recommend using brushes to collect the pollen, because most of it will remain unused among the hairs. Sometimes I take the anther with two fingers and rub it on the stigmas. The use of tweezers facilitates the operation, especially for species that have very small anthers such as those ascribed to the subgenus Decaloba.
They pollute when the flowers of the mother plant (A) are wide open, the stigmas are still pointing upwards and the anthers of the father plant (B) are already supplied with pollen. I have equipped myself with a toolbox containing tweezers, a container divided into numbered sectors to place the anthers of different passifloras, labels progressively numbered with the indication of the year and an indelible marker. I attach a numbered label to the androgynophore on which I have written the name of the two parents (A x B) and the date. In hybrids the name of the mother should always be written first.
I prefer to use the androgynophore for applying the label, as this structure will become the petiole of the future fruit. In my experience, when the fruit is ripe, it detaches from the plant and the predetermined fracture zone is precisely the union between the androgynophore and the flower. Others prefer to put the indication of the hybrid on the flower petiole; however, when the fruit falls, the information about the hybrid will remain on the plant.
I have a habit of using buttonhole labels to which I apply a cotton thread so that I can easily make a loop wrapped around the androgynophore. I have seen that other devices are used, such as wrapping the stem with adhesive paper tape (the one used by coachbuilders) on which the information is written. Everyone can invent what they prefer. To avoid pollution with alien pollen brought by insects, it is advisable to cover the fertilised flower with a lightweight non-woven fabric.
I use this device to cover also the newly-opened parent flowers. In Italy there is an annoying dipteran, Episyrphus balteatus, which is greedy for pollen and capable of eating it all in a short time, thus nullifying the possibility of pollination.
You can see the whole hybridisation process well illustrated here.
If the pollination has been effective, the ovary will begin to swell and within two days you will see the difference. Otherwise the flower will fall. If we are lucky, the fruit will be ripe and full of hybrid seeds within no less than two/three months. It can happen that the fruit grows normally and creates illusions. Once opened it is empty. I call these 'hysterical pregnancies' which are due to the stimulation of fruit growth for hormonal reasons, but not because of successful fertilisation. This happened to me with a beautiful fruit of P. ‘Fata Confetto’ x P. vitifolia, on which I had placed much hope, so much so that I was already dreaming of a red 'Fata Confetto'.
Once the fruit has reached maturity, the seeds must be recovered, cleaned of the aril, sowing some immediately or storing them. To remove the aril easily and obtain clean seeds, you can use a normal kitchen strainer, preferably large, with a mesh such that the seeds cannot pass through. The fruit is opened and the contents are poured into the strainer. A piece of rolled-up cloth is taken, and the seeds with the aril are rubbed under running tap water so that they remain in the strainer, while the pulp and other material is removed by the water. This way the seeds will be perfectly clean. They can be dried and used immediately or stored in a cool place.
We finally have our hybrid seeds and now we have to germinate them, take care of the seedlings as they grow and bring them to bloom. On average it will take two years, but patience will be rewarded. The opening of the first flower of a new hybrid is always exciting and thrilling for me. Sometimes, but rarely, there are disappointments when the flower is of little significance or is a dejà vu.
Usually, however, flowers of extraordinary beauty and elegance open up. Some of these will have a bright future and will be cultivated around the world. I am left with the satisfaction of having enriched our planet with new flowering beauties.