Development of naturalizable lettuce by self-seeding through hybridization with its wild ancestor (Lactuca sativa subsp. serriola).
First published: December 3, 2023
On Joran's Seeds & Research blog:
Last modified: December 22, 2024
Joran Marechal
Joran's Seeds & Research
Saint Vincent de Durfort, Ardรจche department, France.
Email address: joransseedsresearch@gmail.com
Joran's Seeds & Research blog: https://joransseedsresearch.blogspot.com
Abstract:
In an agroecological approach of permaculture or agroforestry, it is desirable to cultivate plants capable of naturalizing.
However, cultivated lettuce (Lactuca sativa subsp. sativa) presents a very strong barrier to spontaneous propagation: its flower heads remain closed after the seeds have matured, so the latter cannot fly away as those of their wild ancestor would do. (Lactuca sativa subsp. serriola).
While this characteristic resulting from human selection is essential in conventional cultivation systems since it facilitates the harvesting of seeds and avoids the uncontrolled propagation of plants, it is however less relevant in the context of an agroecological culture, based on the processes and ecosystem functions.
This trait can be eliminated through hybridization with it’s wild ancestor: Lactuca sativa subsp. serriola.
As part of this project, in 2022, four lines resulting from hybridizations between wild and cultivated lettuces were produced by Joran's Seeds & Research.
Four open-growing, seed-reproducible lettuce cultivars were used as maternal parents, and wild lettuces (Lactuca sativa subsp. serriola) from the local flora of the Ardรจche department in southern France as paternal parents.
Both botanical varieties of the serriola subspecies were used: var. serriola and var. integrifolia, in different combinations.
Ultimately, this project aims to produce naturalizable winter lettuce lines.
Developed for sowing in autumn, very easy to grow in open fields, they will not require irrigation or treatment during cultivation; and will be able to naturalize thanks to the release of their seeds.
Harvested leaf by leaf, as “looseleaf” lettuce at the rosette stage, they can then:
- either be consumed in the “celtuce” type, once erected 30-40cm.
- either be left in place, as reproductive plants, to re-seed themselves according to the wind.
However, the production of commercial quantities of seeds remains possible by growing plants under cover. It will then be possible to harvest almost all of the seeds.
The four combinations and the resulting hybrids are shown in the following photographs:
Buy seeds:
The seeds of the plants mentioned in this article are for sale:
- Lactuca sativa subsp. serriola var. serriola
About 100 seeds (0.1g) / €5
- Lactuca sativa subsp. serriola var. integrifolia
About 100 seeds (0.1 g) / €5
--------
- Light green oakleaf x Lactuca sativa subsp. serriola var. serriola
F2 (harvest 2023)
25 seeds / 5€
- Green canary tongue x Lactuca sativa subsp. serriola var. serriola
F2 (harvest 2023)
25 seeds / 5€
- Light green romaine lettuce x Lactuca sativa subsp. serriola var. integrifolia
F2 (harvest 2023)
25 seeds / 5€
Contact me:
Payments by Paypal
International delivery.
Full article:
Introduction:
In an agroecological approach of permaculture or agroforestry, it is desirable to cultivate plants capable of naturalizing.
However, cultivated lettuce (Lactuca sativa subsp. sativa) presents a very strong barrier to spontaneous propagation: its flower heads remain closed after the seeds have matured, so the latter cannot fly away as those of their wild ancestor would do (Lactuca sativa subsp. serriola).
While this characteristic resulting from human selection is essential in conventional cultivation systems since it facilitates the harvesting of seeds and avoids the uncontrolled propagation of plants, it is however less relevant in the context of an agroecological culture, based on the processes and ecosystem functions.
This trait can be eliminated through hybridization with it’s wild ancestor: Lactuca sativa subsp. serriola.
Description of the serriola subspecies:
The serriola subspecies is the wild ancestor of domestic lettuce.
The plants are thorny: the stem as well as the midrib on the underside of the leaves.
The taste of their foliage is bitter.
The serriola subspecies is subdivided into two varieties:
Besides the morphology of the leaves, the two varieties differ in many ways:
- their root system: the var. serriola has a more robust root system than the var. integrifolia (visible in the photographs above).
- their growth behavior: var. serriola has a biennial or annual habit similar to winter lettuces, with germination in fall or early spring, followed by flowering in late spring/early summer.
While var. integrifolia has an opportunistic annual behavior: new generations of plants can germinate throughout the summer. It is common to see them germinate thanks to the rain in August, and complete their cycle during the fall.
- their vascularization: var. serriola has much more resistant vascular bundles than var. integrifolia. This can be observed by pruning (pulling downwards by hand) the lowest lateral branches of a plant (moreover one meter high). Those of the var. integrifolia are easy to pull out, unlike those of the var. serriola.
- their coloring: result of the presence, or not, of anthocyanins in the tissues. The var. serriola has a purplish stem. While that of the integrifolia variety remains green.
The nothovariety resulting from the hybridization of these two varieties presents a variable leaf morphology:
Sometimes similar to the integrifolia variety at the beginning of their development, then, when the plants rise during their flowering, then present a cut foliage, characteristic of the serriola variety. Or sometimes, leaves with cut and uncut blades are distributed irregularly on the plant.
The hybrids show traces of anthocyanins, but these are attenuated compared to the serriola variety.
Materials and methods:
Sowing took place directly on site, in open fields, at the beginning of September 2021.
Four cultivars of domestic lettuce were used as maternal parents: all open-growing, looseleaf-type, and reproducible seed.
- Three cultivars of the botanical variety crispa:
- And a cultivar of the var. longifolia:
The wild lines used as paternal parents come from the local flora of the Ardรจche department in the south of France. They were collected by Joran Marechal of Joran's Seeds & Research.
Both varieties of the serriola subspecies have been used as paternal parents in different combinations.
Domestic lettuce cultivars, used as maternal parents, were distributed among a large number of wild lettuces, open-pollinated, under field conditions.
The seeds of the lettuce used as maternal parent were harvested during the summer of 2022.
All seeds were sown under cover during the fall of 2022.
Results :
F1 hybrids were identified on the basis of morphological characteristics, and in particular by the presence of spines on the midrib of the lower surface of the leaf as well as on the stem.
Their phenology was intermediate between the two parental lines: the leaf morphotype of their domestic parent remained clearly identifiable, and their rosette was almost as leafy. But they had thorns and a bitter taste.
And their seeds flew away, like those of wild lettuce.
Trait dominance in F1 hybrid:
These four F1 hybrid lines were isolated and self-pollinated.
The F2 hybrids presented a great phenotypic variability:
They presented a relative parity between a leaf morphology very close to wild lettuces, and others, very close to the parental domestic lines.
These two leaf morphologies could be randomly accompanied by a shiny or dull, green or glaucous epidermis; also in a relatively equal manner.
Thorny vegetation was the majority compared to the spineless character. Thorns could appear late in certain plants, sometimes only from the time of the shoot.
The proportion of plants with the trait of “free seeds” versus “closed capitula” could not be counted. However, the free seed trait seems to be in the majority (out of 3 elite plants kept during the winter of 2023-2024, one was found to have closed capitula).
Bitterness also seemed to be in the majority.
Thus, several hundreds, even thousands of individuals from each F2 line had to be observed in order to select “elite” individuals, closest to the desired phenotype.
These individuals were then reproduced in an autogamous manner.
During the winter of 2023-2024, F2 seeds from the lines (Oakleaf X var. serriola) and (Romaine X var. integrifolia) were sown and an elite individual could be selected in each line.
They were self-pollinated.
During the winter of 2024-2025, F2 seeds of the lines (green canary tongue X var. serriola) and (purple canary tongue X var. serriola) were sown and elite F2 plants were also able to be identified and self-fertilized.
Some unintentional hybrids between the different lines have been identified, and thus new morphotypes have been discovered and preserved.
Like this one, which reveals a counterintuitive dominance of the non-lobed morphotype over the lobed one:
Or these, with another type of anthocyanin expression: "blood spots":
Next objectives and purpose:
The selection objectives on the F3 will be: the stabilization of these lines, a selection to eliminate bitterness, the increase in yield and the delay in flowering; while maintaining a very high general resistance.
Ultimately, this project aims to produce naturalizable winter lettuce lines.
Developed for sowing in autumn, very easy to grow in open fields, they will not require irrigation or treatment during cultivation; and will be able to naturalize thanks to the release of their seeds.
Harvested leaf by leaf, as “looseleaf” lettuce at the rosette stage, they can then:
- either be consumed in the “celtuce” type, once erected 30-40cm.
- either be left in place, as reproductive plants, to re-seed themselves according to the wind.
However, the production of commercial quantities of seeds remains possible by growing plants under cover. It will then be possible to harvest almost all of the seeds.
Discussion:
In the description of the varieties of the subspecies serriola, I mention the greater resistance of the vascular bundles of the var. serriola compared to those of the var. integrifolia.
This may explain why the majority of lettuce cultivars grown for their stems (Lactuca sativa subsp. sativa var. angustana) have foliage that is not cut.
Buy seeds:
The seeds of the plants mentioned in this article are for sale:
- Lactuca sativa subsp. serriola var. serriola
About 100 seeds (0.1g) / €5
- Lactuca sativa subsp. serriola var. integrifolia
About 100 seeds (0.1 g) / €5
--------
- Light green oakleaf x Lactuca sativa subsp. serriola var. serriola
F2 (harvest 2023)
25 seeds / 5€
- Green canary tongue x Lactuca sativa subsp. serriola var. serriola
F2 (harvest 2023)
25 seeds / 5€
- Light green romaine lettuce x Lactuca sativa subsp. serriola var. integrifolia
F2 (harvest 2023)
25 seeds / 5€
Contact me:
Payments by Paypal.
International delivery.