Within DRIVE4EU we aim to produce rubber dandelions with a higher rubber and inulin (a polyfructane) yield. According to literature the maximum yield of wild Taraxacum koksaghyz (TKS) is 200 kg per hectare. A higher production can be achieved by improved agronomy and by breeding bigger plants with more rubber and inulin. It is interesting to compare the situation of the rubber dandelion now with that of the rubber tree, Hevea brasiliensis, in the past. At the end of the 19th century, rubber trees produced about 600 kg rubber per hectare. Nowadays, due to better agronomy, but mainly due to the selection for highly productive clones, Hevea rubber production can be up to 2500 kg per hectare.
TKS has been subjected to plant breeding in the past, in the Soviet Union and especially in Sweden. Progress in the Soviet Union was limited, due to the influence of Trofim Lysenko, who denied the existence of genes which was a major drawback for SU plant breeding. The Swedish rubber breeding program was carried out at the Svalof Plant Breeding institute in Southern Sweden. It run from 1945 until 1951. Plants were selected for high rubber content in the roots and the best plants were intercrossed. The results were spectacular; within 6 generations the percentage of rubber increased from 5 to 15 percent on dry weight basis. For comparison: this increase is steeper than the increase in sugar content in sugar beets in the 19th century.
Nearly all modern crops have a long domestication history. One of the most recent crops is root chicory, which was grown and selected for its roots 200 years ago as a surrogate for coffee, which was not available in Napoleon times, due to the British sea blockade. Interestingly chicory belongs to the Asteraceae family and is quite closely related to dandelion. Therefore it may serve as an example of what may be reached by plant breeding in rubber dandelions. Although this is still far away, it is well known that in wild species big improvements can be made, in contrast to already domesticated crops, in which progress is often incremental. The large improvements in Svalof TKS breeding program nicely illustrates this principle. Unfortunately nothing is left of this improved germplasm. In the beginning of the 1950’s there were great hopes for synthetic rubber and the breeding programs were terminated.
In DRIVE4EU we select the best rubber producing plants but also take other traits into account. For example the inulin content of the roots, since the fructoses in inulin can be used as building blocks for bioplastics and other biochemicals. In addition to plant breeding we also propagate seeds which are needed for the agronomical field trials and production plots.
Figure 1. Rubber dandelions grown in a seed nursery for seed production. At densities of 100 000 or more seeds per hectare many seeds are needed.
Figure 2. Variation between dandelion plants in pathogen resistance. The plant to the left is resistant to powdrey mildew while the plant to the left is highly infected and susceptible. Resistance is genetically determined and can be selected for is breeding programs to develop resistant rubber dandelion lines.