1Agriculture and Agri-Food Canada, Saskatoon Research Centre
107 Science Place, Saskatoon, SK, Canada, S7N 0X2
2Department of Plant Sciences, University of Saskatchewan 51 Campus Drive, Saskatoon, SK, Canada, S7N 5A8
The inheritance of hydroxybenzyl glucosinolate content in S. alba was studied in F1, BC1F1, and F2 progeny of a cross between the high glucosinolate variety Sabre (>140 μmoles/g seed) and the low glucosinolate line WD96-2 (<1 μmoles/g seed). Segregation patterns indicated that hydroxybenzyl glucosinolate content in S. alba was controlled by a single gene exhibiting dominance of high over low glucosinolate contents.
KEYWORDS canola-quality meal, hydroxybenzyl glucosinolate
Yellow mustard (S. alba) has the potential to be a major oilseed crop for Canada. It has many advantages over the currently grown canola species Brassica napus and B. rapa including heat and drought tolerance, resistance to blackspot (Alternaria brassicae Berk. Sacc) (Brun et al. 1987), and tolerance to flea beetle attack (Phyllotreta cruciferae Goeze)(Bodnaryk and Lamb 1991). Other desirable characteristics of S. alba include early maturity, pod shatter resistance, large seed size allowing deeper seeding of the crop compared to shallow seeding of the Brassica species (Brandt 1992), and yellow seeds in which chlorophyll levels are not masked in immature seed. Currently, S. alba is grown for condiment mustard purposes in western Canada and its meal contains high levels of glucosinolates while canola-quality meal requires glucosinolate content to be less than 30 :moles/g oil-free meal. Low erucic acid, low glucosinolate forms of S. alba have been developed at the AAFC Saskatoon Research Centre (Raney et al. 1995). The objective of this study was to determine the inheritance of the content of the predominant glucosinolate in yellow mustard, hydroxybenzyl (HObenzyl) glucosinolate. Knowledge of the genetic control of this trait will assist in developing strategies for the breeding of canola-quality S. alba varieties.
Parents for the study of HObenzyl glucosinolate content inheritance in S. alba were the high glucosinolate variety Sabre and the low glucosinolate line WD96-2. Both genotypes were developed at the AAFC Saskatoon Research Centre.
F1, BC1F1, and F2 populations were developed using bud pollination techniques in a controlled environment. F1 seed was produced by reciprocally crossing Sabre with WD96-2. BC1F1 seed was produced by reciprocally crossing F1 plants with each parent. BC1F2 seed was produced by self-pollination of BC1F1 plants. Bulked samples of 10 seeds from parent and F1 plants and 20 seeds from BC1F1 and F2 plants were analysed for glucosinolate content using a modification of the gas chromatographic method of Thies (1980) as described by Raney et al. (1995).
HObenzyl glucosinolate content of Sabre, WD96-2, and F1 plants
The HObenzyl glucosinolate content of seed borne on Sabre was 173 μmoles/g seed and that of seed borne on WD96-2 was <1 μmoles/g seed (Fig. 1). The F1 seed was similar in HObenzyl glucosinolate content to selfed parent seed which indicated maternal control of this trait.
The F2 seed and BC1F1 seed derived from the backcross to either parent borne on the same F1 plant contained similar levels of HObenzyl glucosinolate. The seed borne on all F1 plants contained high levels of HObenzyl glucosinolate (136-181 μmoles/g seed) which indicated dominance of high over low HObenzyl glucosinolate contents (Fig. 2).
HObenzyl glucosinolate content of BC1F1 plants
The frequency distribution of HObenzyl glucosinolate content of BC1F2 seed borne on BC1F1 plants derived from the backcross to WD96-2 segregated into two classes: plants with 1) <1 and 2) >90 μmoles/g seed (Fig. 3). In three of four reciprocal backcross populations, there were no significant differences between the observed ratio and the theoretical segregation ratio for one gene control. However, heterogeneity among the four populations was significant.
The HObenzyl glucosinolate content of BC1F2 seed borne on BC1F1 plants derived from the backcross to Sabre was high (80-185 μmoles/g seed). The frequency distribution was continuous and no segregation ratios were tested (Fig. 4).
HObenzyl glucosinolate content of F2 plants
The HObenzyl glucosinolate content of F3 seed borne on F2 plants ranged from <1 to 188 μmoles/g seed. The frequency distribution of HObenzyl glucosinolate contents of F2 plants segregated into two classes: plants with 1) <12 and 2) >70 μmoles/g seed (Fig. 5). The segregation ratio of 1(low):3(high) for a one gene model with dominance was tested and there were no significant differences between the observed and theoretical segregation ratios in reciprocal F2 populations.
Similar HObenzyl glucosinolate contents of selfed parent seed and F1 seed borne on parent plants indicated that this trait in S. alba seed was controlled by the genotype of the maternal plant. Dominance of high over low HObenzyl glucosinolate contents was indicated by the high level of HObenzyl glucosinolate in all seed borne on F1 plants.
Segregation patterns of HObenzyl glucosinolate content of BC1F1 plants derived from the backcross to the low glucosinolate parent and of F2 plants indicated that HObenzyl glucosinolate content in S. alba seed was controlled by a single gene.
The results of this study indicated that the low glucosinolate trait in S. alba was highly heritable and simply inherited and therefore, could easily be reselected following backcrossing in a breeding program.
Financial support from the following sources is gratefully acknowledged: Saskatchewan Canola Development Commission, Canada-Saskatchewan Agri-Food Innovation Fund, Canadian Seed Growers’ Association, University of Saskatchewan, Canada.
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