Natural rubber is an essential material used in more than 50,000 products, including tires and medical equipment, because of its intrinsic properties such as impact resistance and high elasticity (Cornish, 2017). This strategic commodity is mainly produced by the Para rubber tree, which has specific climate requirements, limiting most cultivation to Southeast Asia (Fox, 2014). Production has been constrained over the past 30 years by conversion of land to palm oil plantations (Dallinger, 2011), and trees are vulnerable to environmental threats, such as disease and climate change, due to low genetic diversity (van Beilen and Poirier, 2007). Increased demand for natural rubber in the future may not be satisfied by rubber tree production alone (Cornish, 2017); therefore, alternative crops are being developed worldwide.
Russian dandelion (TKS) is a promising alternative to the rubber tree (Cornish, 2017). Specialized cells, laticifers, in fleshy tap roots produce milky latex in which rubber particles are suspended (Whalen et al., 2013). Coagulated latex produces solid rubber with properties similar to that derived from the rubber tree. The species is suited to a temperate climate and can be grown in parts of Europe and North America along latitudes similar to those of its native habitats in Kazakhstan, Uzbekistan, and northwestern China (Cornish, 2017). Unlike many dandelion species, TKS is diploid (2n = 16) and sexually reproducing with enforced outcrossing through self-incompatibility (Warmke, 1943). Although a perennial, the plant can be easily incorporated into annual cropping systems.
Extensive TKS cultivation and research was conducted during World War II, during a natural rubber shortage (Whaley and Bowen, 1947). Rubber from this species accounted for 30% of that consumed in the USSR in 1941 (Ulmann, 1951, as cited in van Beilen and Poirier, 2007); however, the species proved difficult to grow and yields were low. Rubber percentage and rubber yield in wild accessions averaged 4.4% of dry weight and 110 kg·ha−1, respectively, across trials conducted in Minnesota, Wisconsin, and Michigan (Whaley and Bowen, 1947). Breeding was initiated for development of high-yielding lines; however, research was suspended after World War II when rubber shortages ceased, and improved TKS germplasm was lost (Kirschner et al., 2013). Thus, initiation of breeding programs today requires access to wild germplasm.
Increasing both root weight and rubber percentage is important for improving rubber yield (Cornish et al., 2016). These traits were not correlated or correlated negatively in both TKS (Cornish et al., 2016; Filippov, 1941, as cited in Whaley and Bowen, 1947), and guayule (Parthenium argentatum), a rubber-producing desert plant (Dierig et al., 1989; Ray et al., 1993; Thompson et al., 1988); consequently, selection for only one parameter may not always improve rubber yield. In guayule, single-plant selection for both root weight and rubber percentage increased rubber yield 300% (Ray et al., 2010). Four years of selection in Russia during World War II produced TKS germplasm with 24.5 g/plant root weight and 15% rubber (Koroleva, 1940, as cited in Whaley and Bowen, 1947).
Although TKS can be grown on sandy soils, those with loam to silty clay loam classifications are optimal for productivity (Whaley and Bowen, 1947). Development of germplasm adapted to different soils could expand acreages suitable for this crop and decrease demand on land used for food production. In areas such as the sandplains of Southern Ontario, where profitable replacement crops for tobacco (Nictotiana tabacum) can benefit growers, breeding TKS for adaptation to light-textured sandy soils could have positive impacts. The objective of this research was to assess the effectiveness of recurrent selection for increasing rubber yield in populations selected separately on sandy and loam soils.
Bowley, S. 2015 A hitchhiker’s guide to statistics in biology: Generalized linear mixed model edition. Plants et al., Guelph, ON, Canada
Cornish, K., Kopicky, S.L., McNulty, S.K., Amstutz, N., Chanon, A.M., Walker, S., Kleinhenz, M.D., Miller, A.R. & Streeter, J.G. 2016 Temporal diversity of Taraxacum kok-saghyz plants reveals high rubber yield phenotypes Biodiversitas (Surak.) 17 847 856
Dallinger, J. 2011 Oil palm development in Thailand: Economic, social, and environmental considerations, p. 24–51. In: M. Colchester and S. Chao (eds.). Oil palm expansion in south east Asia: Trends and implications for local communities and indigenous peoples. FPP and SW, Moreton-in-Marsh, England
Dierig, D.A., Thompson, A.E. & Ray, D.T. 1989 Relationship of morphological variables to rubber production in guayule Euphytica 44 259 264
Falconer, D.S. 1981 Introduction to quantitative genetics. Longman, London, England
Fox, J. 2014 Through the technology lens: The expansion of rubber and its implications in Montane Mainland southeast Asia Conserv. Soc. 12 418 424
Hodgson-Kratky, K.J.M., Stoffyn, O.M. & Wolyn, D.J. 2015 Harvest date, post-harvest vernalization and regrowth temperature affect flower bud induction in russian dandelion (Taraxacum kok-saghyz) Can. J. Plant Sci. 95 1221 1228
Hodgson-Kratky, K.J.M., Stoffyn, O.M. & Wolyn, D.J. 2017 Recurrent selection for improved germination under water stress in russian dandelion J. Amer. Soc. Hort. Sci. 142 85 91
Hoffman, A.A. & Parsons, P.A. 1991 Evolutionary genetics and environmental stress. Oxford University Press, Oxford, United Kingdom
Kirschner, J., Stepanek, J., Cerny, T., De Heer, P. & van Dijk, P.J. 2013 Available ex situ germplasm of the potential rubber crop Taraxacum koksaghyz belongs to a poor rubber producer, T. brevicorniculatum (Compositae-Crepidinae) Genet. Resources Crop Evol. 60 455 471
Moussavi, A., Cici, S.Z.H., Luocks, C. & van Acker, R.C. 2016 Establishing field stands of Russian dandelion (Taraxacum kok-saghyz) from seed in southern Ontario, Canada Can. J. Plant Sci. 96 887 894
Ontario Ministry of Agriculture, Food and Rural Affairs 2014 Vegetable production guide 2014–2015. OMAFRA Publ. 838
Ray, D.T., Dierig, D.A., Thompson, A.E. & Diallo, M.M. 1993 Parent-offspring relationships in apomictic guayule J. Amer. Oil Chem. Soc. 12 1235 1237
Ray, D.T., Foster, M.A., Coffelt, T.A. & McMahan, C. 2010 Guayule: Culture, breeding and rubber production, p. 384–410. In: B.P. Singh (ed.). Industrials crops and uses. CABI, Cambridge, MA
Thompson, A.E., Ray, D.T., Livingston, M. & Dierig, D.A. 1988 Variability of rubber and plant growth characteristics among single-plant selections from a diverse guayule breeding population J. Amer. Soc. Hort. Sci. 113 608 611
Tysdal, H.M., Kiesselbach, T.A. & Westover, H.L. 1942 Alfalfa breeding. Univ. Nebraska, Agr. Expt. Sta. Bul. 124
van Beilen, J.B. & Poirier, Y. 2007 Guayale and russian dandelion as alternative sources of natural rubber Crit. Rev. Biotechnol. 27 217 231
Whalen, M., McMahan, C. & Shintani, D. 2013 Development of crops to produce industrially useful natural rubber, p. 329–345. In: T.J. Bach and M. Rohner (eds.). Isoprenoid synthesis in plants and microorganisms: New concepts and experimental approaches. Springer-Verlag, New York, NY
Whaley, W.G. & Bowen, J.S. 1947 Russian dandelion (kok-saghyz) an emergency source of natural rubber. Misc. Publ. No. 618. U.S. Govt. Printing Office, Washington, DC