| Taraxacum kok-saghyz | |
|---|---|
 | |
| The Russian dandelion | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Asterales |
| Family: | Asteraceae |
| Genus: | Taraxacum |
| Species: | T. kok-saghyz |
| Binomial name | |
| Taraxacum kok-saghyz L.E.Rodin | |
Taraxacum kok-saghyz, often abbreviated asTKS and commonly referred to as theKazakh dandelion,rubber root, orRussian dandelion,[1][2] is a species ofdandelion native toKazakhstan,Kyrgyzstan andUzbekistan, notable for its production of high-qualityrubber.[3]T. kok-saghyz was discovered in Kazakhstan in 1932 bySoviet scientists seeking a domestic source ofrubber.[2][4]
Kok-saghyz is derived from the Kazakhkök-sağız (көк-сағыз), withkök meaning green andsaghyz meaning rubber or gum. Its latex was traditionally used as a kind of chewing gum.[5]
Taraxacum kok-saghyz is a perennial plant with a yellow composite flower characteristic of the genusTaraxacum. Each flower head may be approximately one inch in diameter and be made up for 50 to 90 florets.[6] Plants may contain 25 to 50 leaves arranged in one or more rosettes at the upper end of the root.Taraxacum kok-saghyz can be differentiated from the common dandelion (Taraxacum officinale) by its generally smaller, grayish green leaves and hornlike structures on the bracts surrounding the bud.[6] Flowers are hermaphrodite, insect-pollinated (entomophilous) and are on stalks that reach about a foot in height.Taraxacum kok-saghyz is usually in flower from May through June, with seeds ripening from June through July.[7]
It is adiploid species that reproduces sexually,[2] and produces good pollen.[1] Another species, a triploidapomict that also has horned bracts and produces rubber,T. brevicorniculatum Korol. has frequently been misidentified asT. kok-saghyz.[1][2]
TKS was cultivated on a large scale in theSoviet Union duringWorld War II. The Soviet Union cultivatedTaraxacum kok-saghyz, together withTaraxacum hybernum andScorzonera tau-saghyz, on a large scale between 1931 and 1950—notably duringWorld War II—as an emergency source of rubber when supplies of rubber fromHevea brasiliensis in Southeast Asia were threatened. TheUnited States, theUK,Germany,Sweden andSpain also cultivated the plant for the same reason. During this time period, the highest yields achieved by the U.S. reached 110 kg of rubber per hectare, while the USSR achieved yields of 200 kg of rubber per hectare. The Raisko sub-camp ofAuschwitz was a German-operated production factory for the plant. Some of the women deported on theConvoi des 31000 worked on its production there.[8] With the conclusion of World War II and the return of affordableHevea brasiliensisrubber (which has 8 to 10 times the yield[9]), the majority ofT. kok-saghyz programs ceased.
Taraxacum kok-saghyz does best in loose, well-drained soils with high moisture retention and apH between 5.5 and 8.5, in full or nearly-full sun.[7] The plant grows well intemperate climates.[10] The greatest growth is recorded in soils containing 2–8%organic matter.[11]
TKS produces about 1 million seeds per pound.[10] The seeds readily germinate but grow very slowly despite the early development of a strong root system. Because of their slow growth, the seedlings are vulnerable to being outcompeted by native weeds. Slow growth andweed control remain major challenges in successfully growingTKS today.[12] The direct seeding ofTKS has been identified by researchers as the preferred method for establishing a crop.[10] Field studies showed thatTKSgermination occurs in May.[13] The vulnerability during early life stages is the main reason why the pest risk assessment, conducted by theJulius Kühn institute, revealed little invasive potential forTKS in Germany.[14]
Currently, the main challenges of growingTKS include plantgermination, seedling vigor, growth rate, andweed control. Weed control is ineffective, as current availableherbicides often have undesired side effects such as slowing the plant development or cause plant injuries.[15] However, weed control is inevitable as uncontrolled weed pressure reduces crop survival and plant growth rate. In addition, the cultivation ofTKS in rows is impractical due to themorphology of the plant. Current studies of plantgenome aim to identifygenetic markers to improveTKSgermplasm. Moreover, the development of weed resistance through traditional plant breeding techniques is being investigated.[10]
In 2022, scientists have reported the firstrust disease onTKS in China, caused byPuccinia hieracii. It leads to moderate to high yield losses and poses a potential threat for large scale production ofTKS.[16]
TKS can be harvested after a single growing season.Rubber accumulation begins at germination, peaks at around one year, and then levels off or decreases due to older root tissues being shed and destroyed bymicroorganisms.[17]
Natural rubber (cis-1,4-polyisoprene) is a polymer produced by plants. Natural rubber is obtained from coagulating and refininglatex from plant species.[10] In many of its most significant applications, it cannot be replaced by synthetic rubber alternatives.[4] Some of the unique and unreplaceable properties include abrasion resistance, elasticity, tear and impact resistance, malleability at cold temperatures, and efficient heat dispersion.[18] The production of natural rubber is concentrated in the tropical areas of Asian-Pacific countries, and it comes from thePara rubber tree (Hevea brasiliensis).[19] The natural rubber market is coordinated by the Association of Natural Rubber Producing Countries (ANRPC). This intergovernmental association represents 92% of the world's natural rubber production.[20] There are a number of factors driving the search for alternatives to natural rubber production.
One threat toHevea brasiliensis rubber production is the South American Leaf Blight (SALB) caused byPseudocercosporaulei fungi, which has afflicted conventional rubber production inSouth America since 1934. This blight may spread to theHevea brasiliensis trees inSoutheast Asia, which are genetically very similar to each other and to those of South America. Furthermore, land used for rubber production is being converted topalm-oil plantations in order to producebiofuel, and labor costs reduce the profitability ofHevea brasiliensis plantations, as each tree must be manually tapped in order to harvest itslatex. Rising oil-prices limit the economic viability of synthetic rubbers, and synthetic equivalents often cannot pragmatically replace natural rubber.[4][2] In May 2019 German tire-makerContinental AG announced it was about to begin production of the "first bicycle tyre made with sustainable rubber from dandelions", which it intended to grow on the grounds of its own manufacturing plants, avoiding several of the traditional issues withH. brasiliensis latex—from the long lead-time between planting and cultivating (only six months for the dandelion, rather than seven years for the rubber tree) and volatile prices of the product due to the long transport-distances between places where the rubber can be grown and the company's factories.[21]
Additionally, there are increasing evidence of allergenic reactions to Hevea rubber used in medical devices (gloves, condoms, catheters, and other medical products), potential shortages of supply due to increasing demand (The global market of natural rubber increases annually by 1–3%.[20]), changes in land use, and a general trend towards the replacement of petroleum-derived chemicals with renewables, which are pushing the search for new sources of natural rubber.[1][4]
One of the alternative options isTKS. It contains on average 12% natural rubber and has an average yield of 225–750 kg/ha. Compared tohevea brasiliensis, the yield ofTKS is not enough to cover the cost of both collection and processing.[20] Researchers have started to developTaraxacum kok-saghyz cultivars which are easier to cultivate and which produce more and better rubber as part of a large research project at many institutions.[9][22][2]
An important stage of the rubber production that also plays a role in the success of theTKS as a crop, is the storage of the roots. They should be stored and handled differently depending on the dimension of the roots and the harvesting season. In general, dry roots can be stored for at least nine months in a dry environment. In order to maximise the productivity, small roots (under 10 g fresh weight) are processed or dried immediately after harvesting. For large roots it is better to store them fresh in a refrigerated room. Cold conditions, besides stabilizing the rubber content, also increase the rubber content in the roots due to the cold induction of the rubberbiosynthetic pathway. This is especially important if the harvest time is before the cold season.[23]
Right after harvesting, the roots are washed from dirt and soil. If roots are not directly processed, because of transportation reason, they must be dried and then can be stored for several months under appropriate conditions.
The process of rubber-extraction follows this pattern:
This process recovered well over 90% of the totalrubber in the roots. Another processing option would be the extraction of rubber aslatex.[4]
Inulin produced byTKS is asugar that could be used in non-food applications or be turned intobioethanol through fermentation. The remaining plant biomass could be used to producebiogas.[4] If the plant is cultivated for this by-product, it is important that the roots are not stored in refrigerated conditions, because the roots degrade inulin to provide the substrates for rubberbiosynthesis.[23]
The growing interest innatural rubber increases the interest ingenetically modified organisms. This need is explained by the decrease of natural rubber world resources, the indispensability of natural rubber for industry, and the strategic necessity of a national industry to be independent of the import . The mainbreeding goals are increasing both the percentage of rubber content in the plant and the vegetative mass of the plant.[20] Compared to other rubber producing plant, theheritability of yield related traits are lower, implying a slower breeding progress forTKS.[24]
The rubber percentage and the size of the roots could be increased through open pollinated polycrosses, resulting in doubled rubber yields. The rubber percentage inTKS could potentially be increased through breeding to 15 to 25% of dry weight.[4] Three genes are mainly responsible for the biosynthesis of rubber: REF (rubber elongation factor), SRPP (small rubber particle protein) and CPT (cis-prenyltransferase). The role of thesegenes was proved in 2016 by the Heveagenome sequence analysis. With the insertion of these genes into the nuclearDNA ofTKS, it is possible to increase the content and the quality of rubber in the plant. Genetic engineering allows to increase the rubber content ofTKS in two ways: either through inulin degradation by gene 1-FEN expression or through knockdown of the gene fructan 1-fructosyl transferase (1-FFT), which codes for the fructose involved in inulin synthesis.[20] Regarding the competitiveness with weeds, creating herbicide resistantTKS plants is a possible strategy to solve this problem.Hybridization between rubber dandelionTKS and common dandelion (Taraxacum officinale) has been proposed as a possible way to achieve this resistance.[25]
{{cite journal}}:Cite journal requires|journal= (help)The EU-PEARLS consortium links stakeholders in the EU and elsewhere in the development, exploitation and sustainable use of guayule and Russian dandelion, aiming to establish complete new value creation chains for natural rubber and latex from these plants.
{{cite web}}:Missing or empty|url= (help)Authority control databases: National |
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