Historically, annual flax has been an important source of fiber for cloth and specialty papers, and of linseed oil for the production of paints, oil-based coverings, and the manufacture of linoleum. The importance of flax diminished in the 20th century with the invention of synthetic fibers and oils. However, interest in flax is being renewed with findings of health benefits of oils high in omega-3 fatty acid and demand for natural fibers. Flax oil contains a large proportion of omega-3 fatty acids (about 50 % of total oil as linolenic acid, 18:3) (White, 2000). Clinical studies in humans have shown that diets rich in flaxseed oil result in decreased aggregation of blood platelets and improved cardiac health (Allman et al., 1995).
It is notable that oils found in seeds of annual and perennial blue flax are quite comparable in quantity and quality of oil. Seed yield of annual flax is 2 to 3 times that of perennial flax, consequently L. usitatissimum is the dominant agricultural species for seed production purposes. At present the role of perennial flaxes such as Linum perenne and Linum lewisii is limited to horticultural and renovation purposes. When grown, they do provide a number of ecosystem services. Cold hardy perennial species retain green vegetation late into the fall and begin regrowth early in the spring, contributing to soil stabilization and water retention where they are present (Colson, 2005). They provide a source of nutrition to local fauna, the vegetation is nutritious to livestock and wildlife (USDA, 2007), and the extended flowering period of many of the perennial species provides forage for bees, flower flies and butterflies.
The objective of this research is to develop a perennial flax variety with good seed yield. Two strategies are being attempted to achieve this objective. A) Improvement of seed yield and agronomic characteristics with recurrent selection of wild perennial species of flax. B) Introduction of the perennial trait to cultivated annual flax by interspecific crosses with wild perennials.
Breeding and Selection
For our purposes, the most useful method of categorizing species within the Linum genus is by genome size. Linum species generally fall into two categories: species with 2n=2x=18 chromosomes and species with 2n=2x=30 chromosomes. Annual cultivated flax (Linum usitatissimum) is a diploid species in the group with 2n=30 chromosomes (Gill, 1987), while most of the perennial blue flax species such as (L. perenne) fall into the group with 2n=2x=18 chromosomes. It has been generally observed that species with the same chromosome number are cross-compatible.
For development of a perennial flax variety we assembled a germplasm pool of fifty-five wild perennial and biennial flax accessions from 13 species. Evaluated species originated from North America, Europe, and Asia. Species evaluated from the 2n=30 group, the group most genetically compatible with L. usitatissimum, include: L. bienne, L. flavum, L. tauricum, L. campanulatum, L. sulcatum, and L. thracium.
The 2n=18 group includes perennial blue flax species that are less likely to cross successfully with L. usitatissimum, but tend to be very winter hardy : Linum altaicum, L. austriacum, L. baicalense, L. hirsutum, L. lewisii, L. perenne, and L. tenufolium.
These accessions were grown for two seasons and survived two winters to ensure overwintering ability. Those that overwintered well were used as parents in crosses to develop interspecific flax hybrids. In general, the crosses were made between parents of the same genome size, however some crosses were attempted between 2n=18 and 2n=30 parents.
Initial crosses within the 2n=18 group were successful in several combinations and viable hybrids were obtained of L. austriacum x L. baicalense, L. austriacum x L. lewisii, L. austriacum x L. perenne, L. baicalense x L. hirsutum, L. baicalense x L. lewisii, and L. lewisii x L. perenne. Sixty viable F1 plants were produced as a result of these crosses.
Initial crossing attempts with L. usitatissimum with other 2n=30 species were less successful. With putative hybrid seed developed with crosses of L. usitatissimum x L. flavum, but seed was not viable.
Strategy for the development of 2n=18 flax species into a perennial flax variety with good agronomic characteristics
Flax species with the 2n=18 genome are self-incompatible, making them ideal for domestication and improvement by recurrent selection. The recurrent selection program for this group was initiated with the random mating of the sixty F1 hybrids generated from initial crosses. The progeny of these matings formed the first generation of random mated seed (RM1). RM1 Seed was germinated in the green house and transplanted to the field in space plantings. The plants that survived the winter were intermated to produce the second generation of random mated seed (RM2). Seed of 180 RM2 families carrying germplasm of up to six 2n=18 perennial species were planted into selection rows at 3 locations, St Paul, Lamberton and Carrington, ND. Plants in these RM 3 nurseries were evaluated for height, branching, lodging, flowering habit (determinate, indeterminate), susceptibility to rust, winter hardiness, seed dehiscence, seed yield, and seed size. After evaluation of the data, the seed from the best 10% of RM3 families will be advanced to RM4 nurseries at multiple locations in 2016. Selections to be included in RM4 nurseries are heavily weighted toward yield potential and winter hardiness, but plants with other desirable characteristics such as large seed size will also be included.
Strategy for the development of 2n=30 flax species into a perennial flax variety that retains agronomic characteristics of cultivated annual flax
Crossing attempts within the 2n=30 group will be attempted again in the summer of 2016. The tentative strategy for developing a perennial variety derived from 2n=30 germplasm is to cross annual cultivated flax (L. usitatissimum, 2n=30) to a winter hardy perennial species with a 2n=30 genome, such as L. flavum. To date this cross has not been verifiably achieved. If an interspecific hybrid with L. usitatissimum can be produced, the plan will be to confirm the validity of the hybrid by *cytological method*. The F1 plants, if confirmed as hybrids, will be grown in the field and allowed to naturally self-pollinate, producing F2 seeds. These seeds will then be grown either in the greenhouse or in a winter nursery to produce F3 seed. A sample of F3 seed will then be grown either in the greenhouse or the winter nursery to produce F3:4 seed. The lines derived from these single F3 plants, 200 to 300 of them, could then be used to perform the first year of evaluations in 2006 under certified organic conditions at one or two locations. Plots will be allowed to overwinter to determine winter survival. The best lines based on seed yield, oil quality, and agronomic fitness will be chosen for evaluation in subsequent years.
Kevin Betts, Senior Scientist, Department of Agronomy and Plant Genetics
Brent Hulke, Research Geneticist, USDA-ARS, Fargo, ND
Michael Kantar, Assistant Professor, University of Hawaii
Don Wyse, Professor, Department of Agronomy and Plant Genetics