By decreasing the expression of two genes encoding enzymes that regulate the fatty acid composition, the level of the healthy fatty acid (oleic acid) in the oil of the field cress seeds was increased from 11 to 84 percent. At the same time the unhealthy erucic acid was reduced from 20 percent down to 0.1 percent. The linolenic acid was decreased from 40 percent to 2.6 percent. Linolenic acid is a healthy polyunsaturated fatty acid, but it is unstable at high temperatures.
– This improved oil is suitable for food processing now, especially for frying, says Li-Hua Zhu, professor in plant breeding and biotechnology at SLU, who leads this research project.
She explains that we need to produce more oil from plants – to replace the fossil oil used, for instance, in the chemical industry, and to get more healthy oils for human consumption. There is no oil crop that could tolerate the cold winters in the north of Sweden today, but the field cress, after being completely domesticated, could be cultivated throughout Sweden, and other parts of the world as well in the future.
Field cress has the potential to become a crop that would be excellent in several respects. It is a biennial plant and can function as a catch or cover crop – it ”catches” the nutrient fertilizers from the field or cover the field during the winter when the arable land would otherwise be bare. Field cress can be cultivated together with for example barley or wheat. The plant has around 20 percent seed oil, but the oil quality in the wild type field cress is not useful for food consumption due to its high level of erucic acid.
Emelie Ivarson is a PhD-student in the research project.
– The field cress has a relatively high content of oil in the seeds, but the composition of fatty acids in the oil of the wild field cress is not suitable as foodstuff. Therefore, we have altered the oil composition, Emelie Ivarson explains.
The study shows the possibility to use the field cress for genetic engineering of oils as tailor-made for various end uses. Since fossil oil is environmentally non-sustainable and resources are depleting, it would be great if we could produce more plant oils for different purposes in our fields.
To develop the field cress into an economically viable crop, the researchers are now attempting to increase the oil content from 20 percent to levels around 30 percent. Winter oilseed rape is the major oilseed crop in Sweden and contains more than 40 percent seed oil, but it is only cultivated in southern Sweden due to its weak winter hardiness.
Ivarsson, E., Ahlman A., Lager I., & Zhu, L-H. 2016. Significant increase of oleic acid level in the wild species Lepidium campestre through direct gene silencing. Plant Cell Reports 35: 2055-2063
Visually, it is impossible to see any difference between feeds with or without field cress cake, when the feed is pelleted. And the pigs do not seem to feel any difference in the taste either, at least they didn’t prefer one feed over the other when served the different diets in this experiment. In the beginning of 2016 eight growing pigs were fed with feed containing the so called cake from field cress. The cake is the pulp that is left over after we have pressed oil from the seeds. The pigs were kept in one of the stalls at the Centre for Veterinary Medicine and Animal Science in Ultuna, and for six weeks we gave them feed with zero, four, eight or twelve percent field cress cake.
From this study we can conclude that field cress cake is a tasty feed ingredient to pigs and it does not seem to cause any harmful health effects. However, analysis of the feeds and fecal samples from the pigs showed a higher proportion of indigestible fiber in the feed containing field cress cake, which resulted in a lower digestibility than the control diet without field cress cake. Strategies like dehulling of husk or supplementation of enzymes could probably improve this new potential feed component. It would add an extra value to the future oil seed and catch crop field cress if also the cake from this plant could be used.
Researchers have found variants of thirty important genes in the genome of the oilseed plant field cress (Lepidium campestre) and its relatives. Those genes determine for example the time of flowering, oil quality, and how easily the seeds fall of the plant when mature. The researchers will be using this knowledge to choose the right plants in the domestication of the wild plant.
The project to tame the field cress has been running for about 20 years at SLU. This plant would be suitable for our northern fields in Sweden. As a biennial oil crop, field cress could function as a catch crop as well, by taking up the nutrients in the soil that otherwise would leak out into the lakes and oceans. But the plant has a couple of ”wild” traits that are not fit for cropping, and it is the variation in those that the researchers have identified.
The interesting variation was found both within the field cress species and between species belonging to the genus Lepidium. The idea is that this knowledge about the genetic variation can help to speed up the domestication of the oilseed crop. The identification of this variation in the genes also reveals something about how the species within the genus Lepidium have changed during the evolution. Field cress is more closely related to Smith’s pepperwort (Lepidium heterophyllum)than to the pepperwort Lepidium hirtum.
– We studied the closely related pepperworts Lepidium heterophyllum and Lepidium hirtum in order to exploit some of their good qualities by crossing them with field cress, explains Cecilia Gustafsson, one of the researchers behind the study.
Field cress is also fairly closely related to the model plant thale cress (Arabidopsis thaliana), a species that is very well studied in terms of which genes that controls different traits. This was something that the researchers could make use of. They looked for genes in field cress that was similar to known genes in thale cress, and thereby they could identify the genes for venalization, florescence, pod shattering and quantity and quality of oil.
Gustafsson, C., Willforss, J., Lopes-Pinto, F., Ortiz, R. & Geleta, M. Identification of genes regulating traits targeted for domestication of field cress (Lepidium campestre) as a biennial and perennial oilseed crop. BMC Genetics, 2018, 19:36 doi: 10.1186/s12863-018-0624-9