Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, SK., Canada, S7N 0X2
The U.S. Food and Drug Administration distinguishes edible oils on the basis of their saturated fat content. Saturated fat content is a labelling requirement for foods sold in the U.S. Low saturated fat oil is defined as oil containing less than one gram saturated fat per fourteen grams of total fat, or less than 7.1%. Until recently canola has been the only oil that meets this criterion. However, with the significant shift in acreage of canola grown in Western Canada away from Brassica rapa to Brassica napus in recent years, this marketing advantage of canola is seriously threatened. As B. napus canola averages 7% saturated fat, a significant portion of commercially grown seed lots, depending on year and location, do not meet the low saturated fat criterion. Low saturated fat B. napus germplasm was identified in breeding populations of the Saskatoon Research Centre. The breeding material was derived from interspecific crosses of B. napus with B. rapa and B. oleracea. Lines were identified that had saturated fat levels similar to B. rapa (less than 6% of total fat content expressed as the sum of myristic, palmitic, stearic, arachidic, behenic and lignoceric acids; less than 5% expressed as the sum of myristic, palmitic and stearic acids). This population also segregated for low linolenic acid content. This material is now being used in the breeding program to develop low saturated fat B. napus varieties for western Canada. The results from two years of field trials are discussed.
KEYWORDS: fatty acid composition, Argentine canola
Canola is Canada's major edible oilseed crop. Its value is determined in large part by the value of the derived oil. High levels of saturated fats, such as palmitic and stearic acid, in the human diets have been positively correlated with cardiovascular disease. As a result edible oils have been categorised according to their level of saturated fat. The two lowest categories are preferred, ‘zero’ (less than 3%) and ‘low’ (less than 7%) saturated fat. Canola oil is in the ‘low’ saturated fat category. Canola oil has a well-deserved reputation as superior, ‘healthy’, edible oil because of its low level of saturated fat, high level of monounsaturated fat and moderate level of polyunsaturated fat. It is particularly recommended for its low level of saturated acids and good frying stability (Labell 1987). Its frying stability has been extended by the development of low linolenic acid cultivars (Eskin et al. 1989, Prevot et al. 1990, Przybylski et al. 1993 and Scarth et al. 1988). Canola oil has penetrated nearly all markets for edible oil, including the shortenings, margarine, cooking oil and salad oil markets. Its ability to keep products in the ‘low’ saturated fat category, which thereby alleviates nutritional concerns, is a major factor in this. However, improvements in the saturated fat level of canola oil have not been achieved. In fact in recent years the level of saturated fatty acid content in Canadian canola has been increasing until in 1998 the average total saturated fat (TSF) content for the crop was 7.0% (DeClerq et al. 1997). This is due to the shift in production in Western Canada from Polish (Brassica rapa) canola to Argentine (Brassica napus) canola. Historically, production was almost evenly split between the two species, but now production is more than 80% Argentine type. The level of TSF in canola oil varies from location to location, region to region and year to year, but Argentine canola averages nearly 7% (Raney, unpublished, DeClerq et al. 1996, 1997). Polish canola TSF is significantly lower, approximately 5.5%. The high saturated fat content in Manitoba canola (almost all Argentine-type) means that this canola oil needs to be blended with Polish canola, an increasingly rare commodity, in order to meet ‘low’ saturated fat requirements. As the Canadian crop continues to shift towards more Argentine and less Polish production for agronomic reasons, it will become more and more difficult for canola oil to meet the 7% standard. Even as Canadian canola oil risks losing its status as a low saturated oil, canola’s position as the only ‘low’ saturated oil is about to challenged by the development of low saturated fat soybean lines (Fehr et al. 1991 and Burton et al. 1994). Low linolenic acid lines of soybean have also been identified (Wilcox et al. 1984). The need to develop truly low saturated fat Argentine (B. napus) canola oil is urgent. This paper describes our identification of germplasm with saturated fat levels similar to B. rapa within a B. napus breeding population derived from interspecific crosses of B. napus with B. rapa and B. oleracea.
MATERIALS AND METHODS
Parental materials and progeny
RSYN1-43 (Raney and Rakow 1995) was a ‘zero’ aliphatic glucosinolate selection from interspecific crosses between a yellow seeded B. napus line YN90-1016, the yellow seeded B. rapa cultivar AC Parkland and light-brown seeded B. alboglabra. TO95-1299 was derived from a cross between the low linolenic acid B. napus cultivar Apollo and YN90-1016. The high oil content, blackleg resistant parent N93-1526 was derived from a cross between an adapted B. napus canola line and Shiralee, a highly blackleg resistant cultivar from Australia. Reciprocal crosses were made between RSYN1-43 and TO95-1299. The F1 of this cross was then crossed with N93-1526. The F1 progeny of this three-way cross was then used for doubled haploid (DH) production via microspore culture and/or selfed and the succeeding generations selected for phenotypes combining the above mentioned traits of the parents. Over 400 DH lines were generated and 244 of these evaluated in the field in either 1997 or 1998; 79 lines were evaluated in both years. Additionally, another 387 F3, F4 and F5 progeny lines were evaluated in the 1998 field nursery. These lines had been selected for low linolenic acid, ‘zero’ aliphatic glucosinolate, light seed colour, and resistance to blackleg. Some of the F3 and F4 lines were pre-selected for low saturated fat content as well.
The fatty acid composition of bulk seed samples and germinated half-seed was determined by gas chromatography of the methyl esters (Thies 1971, Raney et al. 1995). Fatty acid content of individual fatty acids was calculated as percent of total fatty acid content (weight basis). Total saturated fat (TSF) was expressed as the sum of the percent contents of lauric, myristic, palmitic, stearic, arachidic, behenic and lignoceric acids. The field nurseries consisted of single rows three metres long with two replicates.
RESULTS AND DISCUSSION
Diploid progeny and inbred F4 and F5 progeny
The progeny of this cross segregated for TSF content in both nurseries (Figure 1). Analysis of variance indicated that there were significant differences between the lines in both years. In 1997 TSF content varied from 5.5 to 7.7% among lines. In 1998 it varied from 5.4 to 8.1%. Of lines (DH progeny and parents) that were entered in both years the average TSF content in 1998 was 6.85%, 0.48% higher than the 1997. As well, the average polyunsaturated fatty acid content was lower in 1998 than in 1997 (data not shown). Segregation for extremes of ‘aliphatic’ glucosinolate, oil and linolenic acid content, and seed colour was observed in both nurseries as well. The TSF content of the entries appeared to be unassociated with any of the other traits. In the 1998 nursery inbred progeny tended to have a lower TSF content than the DH progeny (Figure 1b), possibly because some prior selection of low TSF had occurred in these progenies.
Figure 1. Histogram of TSF content in progeny grown in field nurseries: a) 1997, b) 1998
Best lines and parents
Table 1 lists some of the best lines observed in the two nurseries. An additional 32 lines in the 1998 nursery had TSF contents less than 6.0% (data not shown). The progeny lowest in TSF, from both DH progeny and inbred progeny, had a TSF content similar to the B. rapa canola cultivar ‘AC Parkland’ about 1.5% lower than the average of the B. napus checks. Line ‘TO97-1299’ had the lowest TSF of the parents, averaging 6% over two years of testing. It was likely segregating for the low TSF trait and for low linolenic acid. Lines ‘TO97-3197’ and ‘TO97-3197-1’ are direct selections out of this parent. The linolenic acid in the low TSF lines varies from 2% to 14% so it appears that the low TSF trait can be selected in both low linolenic acid B. napus canola and in standard B. napus canola.
Table 1. Total Saturated Fat and Linolenic Acid Content of parents, selected lines and checks
The saturated fat content expressed as the sum of lauric, myristic, palmitic and stearic acids is consistently about 1% less than the TSF value (data not shown). In general the lower TSF content in these lines is not the result of any one particular fatty acid being dramatically lower, but rather the result of all saturated fatty acids being somewhat lower.
Lines of B. napus canola have been identified in a population resulting from interspecifc crosses with B. rapa and B. oleracea, which are significantly lower in total saturated fat content than standard B. napus canola. These lines have a TSF content similar to B. rapa canola well within the parameters set out by the U.S. Food and Drug Adminstration for ‘low’ saturated fat edible oil. The TSF content of these lines is less than 6% and if saturated fat content is calculated on the basis of fatty acids up to 18 carbon atoms long (Sum of lauric, myristic, palmitic and stearics acids) it is less than 5%. If the ‘low’ TSF trait of these lines is integrated into elite B. napus cultivars the world markets can be assured that Canadian canola oil will continue to be ‘low’ saturated fat oil. This work has been initiated at the Saskatoon Research Centre.
The authors acknowledge the support of the Canola Council of Canada and the Matching Investments Initiative program of Agriculture and Agri-Food Canada for this project.
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