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Katrina J.M. Hodgson-Kratky and David J. Wolyn

Russian dandelion (Taraxacum kok-saghyz) is a candidate species for introducing natural rubber production into North America, and its domestication is currently underway to create an economically viable crop. Development of hybrid cultivars is essential to maximize the yield potential of the species, and cytoplasmic male sterility (CMS) is an important breeding tool that can facilitate this process. Male sterility was discovered in two full-sib russian dandelion families, and additional crosses were performed to create F2, F3, and backcross generations to assess inheritance of the phenotype. A sterility-inducing cytoplasm (S) that could be restored to fertility by a dominant allele at a single nuclear restorer of fertility (Rf) gene and a fertility-inducing cytoplasm (F) were identified. Characteristics of the CMS system were 1) (S)rfrf × (F)rfrf crosses produced only sterile progeny, 2) crosses where the female parents were (F) produced only fertile progeny, and 3) segregation was observed only when the maternal parent had (S). Sterility was not stable in all plants; some with sterility-inducing cytoplasm produced small amounts of pollen or formed both sterile and fertile flowers simultaneously. On the basis of seasonal differences in the frequency of partially sterile plants, sterility was stable at low temperatures and unstable at high temperatures. This germplasm can be of central importance for development of stable CMS lines for hybrid production.

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Katrina J.M. Hodgson-Kratky and David J. Wolyn

Russian dandelion [Taraxacum kok-saghyz (TKS)] is a latex-producing, temperate species that has the potential to be grown as a source of natural rubber in North America. Flowering habit varies within the species; winter-type plants require a cold period or vernalization to flower, whereas spring-type plants flower without this treatment. Because flowering habit is correlated with rubber yield, understanding the genetic factors governing the trait would be useful for breeding. The objective of this research was to determine the inheritance of vernalization requirement in TKS. Winter-type and spring-type plants were intercrossed to create the F1, F2, and backcross generations and progeny segregation ratios were analyzed. A genetic model with three major genes is proposed, where a dominant allele at locus A, in combination with homozygous recessive alleles at either or both of two loci, B and C, confers winter type, whereas spring type is conferred by homozygous recessive alleles at A, regardless of genotype at B or C, or dominant alleles at A, B, and C.

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Katrina J.M. Hodgson-Kratky, Olivier M. Stoffyn and David J. Wolyn

Russian dandelion [Taraxacum kok-saghyz (TKS)] is a promising alternative to the Para rubber tree (Hevea brasiliensis) as a source of natural rubber; however, rubber yields must be improved for this undomesticated species to become a profitable new crop. Half-sib family recurrent selection was conducted for four cycles to increase rubber yield, estimated as the product of rubber percentage, and root dry weight per plant. Two distinct populations were developed for adaptation to sand and loam soil types. Rubber percentage increased from 4.17% for the cycle 0 (C0) population to 6.40% for the C4-loam population. Rubber yield also increased from 0.15 to 0.22 g/plant after four selection cycles. Although phenotypic variation was observed, selection had no effect on root weight; all populations averaged 3.70 g/plant. Rubber yield and percentage and root dry weight were not increased after four selection cycles on sandy soils, likely because of poor adaptation and high environmental variation. Year and soil type affected rubber yields; however, rubber percentage was more stable than root dry weight. Overall, russian dandelion can be improved for rubber yield, and further studies with increased error control should be considered to enhance root dry weight.

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Katrina J.M. Hodgson-Kratky, Olivier M. Stoffyn and David J. Wolyn

Russian dandelion [Taraxacum kok-saghyz (TKS)] is a promising candidate for introducing natural rubber production into North America. Seeds normally germinate in a humid microenvironment, such as the thatch layer of a lawn or under a canopy of grass; however, 5% to 15% establishment is often observed on bare soil, presumably due to water stress. Phenotypic selection and half-sib family recurrent selection were conducted for three cycles to improve germination in vitro, under low osmotic potential (Ψs), using a polyethylene glycol (PEG) solution. Populations were then tested for establishment on bare soil in the greenhouse and field. Germination under water stress in vitro increased from 5.8% for the cycle 0 (C0) population to 40.8% and 47.8% for the C3-phenotypic and C3-half-sib family populations, respectively. Soil establishment in the greenhouse and field was improved up to two- and 4-fold, respectively, compared with the C0, in two of four greenhouse experiments and three of eight field experiments. Overall, recurrent selection for germination under water stress in vitro has potential to improve establishment in the field and can be incorporated into current breeding programs to support the overall goal of creating cultivars with high-rubber yield.