THE DEVELOPMENT OF LOW ALIPHATIC, LOW INDOLE GLUCOSINOLATE BRASSICA RAPA
D.S. HUTCHESON1, K.C. FALK2 and G.F.W. RAKOW2
1Western Grower Seed Corp., 144 Jessop Ave., Saskatoon, SK., Canada S7N 1Y4
2Agriculture and Agri‑Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, Saskatchewan, Canada S7N 0X2
Glucosinolates are sulfur-containing compounds present in many plant families but most often associated with the Cruciferae. The discovery of the reduced aliphatic glucosinolate trait in the B. napus cultivar Bronowski resulted in the development of B. napus and B. rapa cultivars with glucosinolate concentrations less than 30 :moles g-1 oil free meal. Subsequent breeding efforts at the Saskatoon Research Centre of Agriculture and Agri-Food Canada have reduced the levels of the aliphatic glucosinolates to approximately 2 :moles g-1 oil free meal in the B. rapa strain BC86-18. However, the 4-hydroxy-3-indolylmethyl glucosinolate content remained unchanged. B. rapa strains with reduced indole glucosinolate content were also developed at Agriculture and Agri-Food Canada and subsequently crossed with BC86-18. Selection for reduced aliphatic and indole glucosinolates began in the F2 generation and continued to the F6. Meal from the low aliphatic, low indole strain, with 4.2 :moles g-1 total glucosinolates, is currently being evaluated in feeding trials in collaboration with the Canola Council of Canada.
KEYWORDS: Turnip rape, canola, glucosinolate, protein meal
Defatted rapeseed meal contains approximately 45% protein on a dry weight basis. The amino acid composition of the protein is well balanced and considered equivalent in quality to soybean protein. However, rapeseed meal utilization is limited by the anti‑nutritive effects of the breakdown products of glucosinolates. Glucosinolates are sulfur‑containing compounds present in many plant families but most often associated with the Cruciferae.
The discovery of the reduced aliphatic glucosinolate trait in the Brassica napus cultivar Bronowski (Krzymanski 1970) resulted in the development of B. napus and B. rapa cultivars with less than 30 Fmoles glucosinolate per gram of oil free meal. The first low glucosinolate summer rape, cv. Tower, was registered in 1974 (Stefansson and Kondra 1975) and the first summer turnip rape, cv. Candle, was registered in 1977 (Anonymous 1977). Subsequent breeding efforts have reduced the levels of the aliphatic glucosinolates to approximately 2 Fmoles g-1 oil free meal in the Agriculture and Agri-Food Canada B. rapa strain BC86‑18. However, the 4‑hydroxy‑3‑ indolylmethyl glucosinolate content, which now constitutes approximately 75% of the residual glucosinolates in canola seed, remained unchanged.
BC86-18 is a canola quality strain derived from the B. rapa cultivar Tobin. Low glucosinolate plants with good yellow seed colour were selected from Tobin and evaluated in progeny rows in 1985. Selected progeny with very low glucosinolate content were inter-crossed and progeny were selected on the basis of glucosinolate content. Five plants from each selected cross were inter-pollinated, bulked and sown in a composite crossing block in 1986. Two cycles of recurrent selection involving 800 progeny in 1987 and 1847 progeny in 1994, respectively, were evaluated in replicated nurseries. A total of 151 progeny were selected on the basis of high seed oil content, average height, ultra-low glucosinolate content (<2 Fmoles g-1), and good agronomic performance following the second cycle of recurrent selection.
DLY is a strain derived from crosses between a population closely related to the B. rapa cv. Candle and the high glucosinolate high erucic acid cultivar R500 (B. rapa ssp. sarson Prain). Sixty-seven yellow seeded F2's were selected and bulked for a field increase and 1000 single plants were harvested. Fifty single plants were selected for low glucosinolate content using the rapid glucose test strip method. From these 50 plants, 99 zero erucic half-seeds were grown, inter-pollinated and harvested individually. Twenty-five individuals were selected from these plants for low glucosinolate content and bulked for a field increase in 1985. Thirty low glucosinolate plants from the field increase were selected, and twenty progeny of each were bud-selfed and inter-pollinated in the greenhouse. Open-pollinated seed was analyzed using a modification of the gas chromatographic method of Thies (1980) as described by Raney et al. (1995). Seven families were identified with low glucosinolate content. Ten reserve seeds of each plant were used to sow the next two cycles of selection. Finally, seven very low glucosinolate plants were selected and crossed in a half-diallel, inter-pollinated and bud-selfed. Seed from one plant was selected on the basis of low glucosinolate content and designated as DLY.
TR4 was derived from crosses between BC86-18 and DLY (Figure 1). Twelve field grown F2 plants were selected with an average aliphatic + indole glucosinolate content of 1.63 Fmoles g-1 oil free meal. Fifteen seeds from each were sown in the greenhouse, inter-pollinated and bud-selfed. Open-pollinated seed was analyzed for glucosinolate content in this and all subsequent cycles of selection. Selfed seed from selected low glucosinolate F3 plants was bulked and sown in a field isolation. Approximately 900 F4 plants were harvested individually and subsequently screened for low glucosinolate content. Twenty-two low aliphatic, low indole glucosinolate plants were identified and 10 F5 seeds from each were sown in the greenhouse, bud-selfed and inter-pollinated. Open-pollinated seed from each F5 plant was assessed for seed colour and glucosinolate content. Seventeen plants were selected with good quality seed, yellow seed coat colour and low glucosinolate content. Again, ten F6 seeds from each plant were sown in the greenhouse and plants were bud-selfed and inter-pollinated. Each plant was also visually assessed for bud and flower abnormalities. Open-pollinated seed from each plant was analyzed for glucosinolate content and approximately 114 F6 plants were selected for progeny row evaluation. Final selection was based on low glucosinolate content (4.2 Fmoles g-1 total aliphatic + indole) and good plant vigour.
TR4 is the first B. rapa strain essentially free of glucosinolates. Meal from TR4 is currently being evaluated in animal feeding trials in collaboration with the Canola Council of Canada.
Developmental work was funded entirely by Agriculture and Agri-Food Canada, Saskatoon Research Centre. Funding for the commercial increase of TR4 was provided by the Canola Council of Canada. Dr. J.P. Raney is gratefully acknowledged for developing the method to determine indole glucosinolate content. The technical assistance of Patricia Tampe, Darryl Petersen, S. Gore, D. Williams, N. Suttill, D. Rode and C. Powlowski are gratefully acknowledged.
Anonymous. 1977. Description of a cultivar: >Candle=. License No. 1754 issued March 29, 1977. Agriculture Canada Production and Marketing Branch, Plant Products Division, Ottawa, Ontario.
Krzymanski, J. 1970. Inheritance of thioglucoside content by rapeseed (Brassica napus). Journees Internationales sur le Colza. C.E.T.I.O.M. pp.212-218.
Raney, P., G. Rakow and T. Olson. 1995. Development of low erucic, low glucosinolate Sinapis alba. Rapeseed today and tomorrow. 9th International Rapeseed Congress, Cambridge, UK. 4-7 July 1995, Vol.2:416-418.
Stefansson, B.R. and Kondra, Z.P. 1975. Tower summer rape. Can. J. Plant Sci. 55:343-344.
Thies, W. 1980. Analysis of glucosinolates via Aon-column@ desulfation. Proceedings of Symposium AAnalytical Chemistry of Rapeseed and its Products@ Winnipeg, pp. 66-71.