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The wild flora holds a number of plant species that, even though we might not be aware of it, represent an important part of what we call genetic resources. Often lacking the physical characteristics that otherwise would make us pay attention, such as e.g. spectacular flowers, they are regularly equipped with different types of defenses like spines or thorns, burning or sticky glandular hairs, or bitter flavors. A good example of this is prickly lettuce (Lactuca serriola L.).
The species belongs to the same genus as our commonly cultivated lettuce (Lactuca sativa L.) which includes garden lettuce (or the Capitata-Group that includes ‘iceberg’ lettuce), leaf lettuce (Crispa-Group) and cos lettuce (Romana-Group). The genus was named Lactuca because of the white milky juice (lac in Latin) that emerges when the cutting the stalk. Even today, we still find the word in lactose (milk sugar) as well as in the French lait and Italian latte. The species name serriola also comes from Latin with the word serra meaning a saw. This refers to the needle-thin spines of the main nerve on the under-side of the leaf and the lower part of the stem.
Prickly lettuce grows quite commonly in the Nordic countries, particularly in ruderal or ‘man-made’ areas, i.e. ‘wastelands’ surrounding industries, rail yards and ports. The species is annual or biennial, about 1 m high, and is characterized by small and quite bright yellow dandelion-like flowers. The seeds, carrying a small ‘parachute’ when ripe, spread efficiently with the wind like most other members of the family Asteraceae. The leaves are deeply lobed and positioned 90 degrees to the stem, making the species easy to recognize.
Many breeders, especially in the Netherlands where the development of new lettuce varieties is intense, have used prickly lettuce extensively. It has mainly served as a source of resistance to diseases and pests, of which troublesome pests include lettuce downy mildew and different species of aphids. The species has also been used as a crossing bridge to facilitate transfer of valuable resistance genes between garden lettuce and even more distantly related species such as wild lettuce (L. virosa L.). To begin with, crossings were made between prickly lettuce and wild lettuce and, thereafter, the resulting progeny could be further crossed with L. sativa. As an example, in 2010 commercial lettuce production in California alone valued 1.24 billion USD (cit. McCreight & Liu, 2012) so any measures to reduce losses by pests and diseases in lettuce pays well off.
This example clearly shows that crop wild relatives very often hold exciting and valuable genetic variation. However, valuable genes are unfortunately often difficult to access due to genetic incompatibilities between plant taxa. Closer collaboration between researchers and plant breeders can therefore only be warmly encouraged.
Text by Jens Weibull, photos by Ingemar Tönnby and Jens Weibull
Contact person: Anna Palmé, anna.palme@nordgen.org
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