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Flax flowers

Flax Breeding Project Objectives

1) Develop and evaluate genetic material to improve yield potential while maintaining resistance to pests, maintaining oil content and oil quality and maintaining other agronomic characteristics for potential cultivars.
2) Develop and maintain populations with useful genetic variability.

Breeding Background

Excellent genetic and breeding reviews have been published (Kenaschuk, 1975;  Gill, 1987).  Flax has been domesticated for a long period of time with unique characteristics.  The main breeding objectives of most flax improvement programs are increased seed yield while maintaining or improving other characters.  Present cultivars have good to excellent resistance to flax rust [incited by Melampsora lini (Ehrenb.) Desmaz.] with adequate tolerance to wilt [incited by Fusarium oxysporum Schlechtend.: Fr. F. Sp. Lini (Bolley) W.C. Snyder & H. N. Hans.] and other diseases.  Processors would appear to prefer high oil content and high linolenic acid (no direct price advantages reported for the producer).  Flax has been seeded later than the date for maximum seed yield production (Stoa and Smith, 1948).  Improvement in seed yield of late seeded flax has been a part of the flax program at North Dakota State University for many years, but progress has been very slow.  Seed yields in late seeded trials are frequently very low.  Differences in genetic potential are difficult to identify in low response growing conditions.  Date of sowing studies (Flor, 1954) indicate that the yield of flaxseed becomes progressively less with delayed seeding.  However, growers continue to seed flax after other crops are seeded in the spring. Cultivars recommended for early seeding frequently are not satisfactory when seeded late.  Additional effort must be expended to produce early maturing cultivars as well as the more desirable late maturing, and likely high yielding, cultivars.

Physiological specialization of Melampsora lini was first demonstrated by Flor (1935).  Studies on the inheritance of reaction to flax rust and on the genetics of pathogenicity in the rust organism have indicated that for each gene conditioning resistance to rust in the host there was a specific gene for pathogenicity in the pathogen.  Utilizing existing germplasm, evaluation of cultivars of flax resistant or immune to North American races of rust should involve only routine greenhouse testing.  In 1973, the change of races of flax rust attacking flax generated interest in the development of cultivars with more than one source of resistance to known local races.  A system was proposed (Hammond, 1978) to utilize races of rust in the development of two-gene cultivars.  At that time, only selected genetic backgrounds with selected gene combinations could be evaluated without extensive backcrossing. Cultivar development with two effective genes conditioning resistance to all known North American races of rust have resulted in the release of several cultivars including 'Flor' and 'Linton'.  The development of cultivars with at least two genes for resistance is more time consuming and requires greater cooperation with plant pathologists than breeding for single gene resistance.  Statler (1981) developed races of flax rust to assist the breeding of multiple gene lines.  With rust races now available for testing, two-gene sources of resistance can be incorporated into a wider background of material.

Much of the soil in the North Central flax growing area is infested with the wilt organism.  An established testing program of seeding in infested soils is available for evaluation of wilt tolerance.  ‘Plot 30' was established as part of a rotation study in the 1880s.  The continuous flax plot has been grown to flax every year since 1884.  Bolley was successful in using the ‘Plot’ to select wilt tolerant flax cultivars.  All cultivars grown in the flax growing region of North America have used the ‘Plot 30' in the development phase or final testing prior to release for production.

Pasmo (Septoria linicola Speg. Garass), a disease generally considered to be of minor importance, has caused considerable damage to flax in certain areas in the flax growing area.  Although no cultivar of flax is classified as resistant to the pasmo organism, cultivars vary in degree of susceptibility.

Population Improvement Background

With the increased interest in flax as a human food, several areas of population improvement are needed.  The USDA flax collection has been screened for lines that have low accumulation of seed Cd (Hammond et al., 1999).  Selected high and low lines have been crossed with various sources of yellow-seeded flax parents.  The F1 seed has been sent for grow out and seed Cd determination.  From these initial crosses and evaluations, selected lines will be intercrossed to form a diverse population for agronomic improvement while breeding for low Cd accumulation.

Several sources of yellow seed coat color are maintained in the USDA flax collection (Miller et al., 1982).  Lines have been selected for crossing in the Cd study.  These materials should also prove useful in describing the genetics of seed color.  The goal would be to develop a population of a stable bright yellow seed coat color for the human food market.  Presently, the yellow-seeded cultivar ‘Omega’ has a small percentage of non-yellow seeds.  Attempts to purify Omega have not been successful.

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