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Crop Science 41:26-29 (2001)
© 2001 Crop Science Society of America

CROP BREEDING, GENETICS & CYTOLOGY

Combining Ability in Loci for High Oleic and Low Linolenic Acids in Soybean

Shaikh M. Rahmana, Takehito Kinoshitab, Toyoaki Anaic and Yutaka Takagic

a Dep. of Genetics and Breeding, Rajshahi Univ., Rajshahi 6205, Bangladesh
b Saga Prefectural Agricultural Research Center, Kawasoe, Saga 840-2205, Japan
c Lab. of Plant Breeding, Fac. of Agric., Saga Univ., Saga 840-8502, Japan

Corresponding author (takagiy{at}cc.saga-u.ac.jp)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Two soybean [Glycine max (L.) Merr.] germplasm lines have been identified for unique fatty acid content. The contents of oleic and linolenic acids in HOLL are controlled by ol and fan loci, respectively, and the very low content of linolenic acid in LOLL is controlled by fan and fanxa loci combined. The fan locus is identical for both HOLL and LOLL. Therefore, if ol and fanxa loci are independent, soybean germplasm could be developed with more unique and useful combinations of these fatty acids. The objectives of this study were to combine the loci of high oleic and low linolenic acids, and determine the effects of altered contents of oleic and linolenic acids on other fatty acids. HOLL was reciprocally crossed to LOLL. The data from F2 seed indicated that the ol locus controlling high oleic acid was independently inherited from the fanxa locus controlling low linolenic acid. Thus, the germplasm (DHL) with the high oleic acid trait from HOLL, and very low linolenic acid trait from LOLL, was easily developed. The increases in oleic acid due to ol was associated completely with changes in linoleic acids, indicating a pleiotropic effect of the ol locus. Decreases in linolenic acid due to fan and fanxa were associated primarily with increases in linoleic acid. The development of DHL with increased contents of oleic acid and decreased contents of polyunsaturated fatty acids could open new markets for soybean oil.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
COMMON SOYBEAN CULTIVARS produce oil with an average of 240 g kg-1 oleic, 540 g kg-1 linoleic, and 80 g kg-1 linolenic acids (Schnebly and Fehr, 1993). Generally, an oil with a high content of monounsaturated fatty acid (i.e., oleic acid) is less susceptible to oxidative changes during refining, storage, and frying. This oil can be heated to higher temperatures without smoking, so that food is cooked faster and absorbs less oil (Miller et al., 1987). Furthermore, the quality of this oil is retained longer during storage than that of oil with a high content of polyunsaturated fatty acids, which is important to processors (Robertson and Thomas, 1976). On the other hand, the high content of polyunsaturated fatty acids (i.e., linoleic and linolenic acids), and especially linolenic acid, limit the utility of an oil for cooking unless it is hydrogenated (Rakow and McGregor, 1973). During this chemical treatment, not only are unsaturated fatty acids converted into saturated fatty acids, but also many positional and transisomers not normally found in nature are produced. There is evidence that the intake of these artificial fatty acids is related to the risk of developing heart disease (Willet and Ascherio, 1994). Consequently, there is an increasing interest from food industries and consumers in producing oil crops with high contents of oleic acid and low contents of polyunsaturated fatty acids that would present a highly nutritional oil. Some rapeseed [(Brassica napus L.), (B. rapa L.)] lines were developed toward this goal by Auld et al. (1992).

Since oleic acid in soybean oil was found to be quantitatively inherited (Burton et al., 1983; Hawkins et al., 1983; Carver et al., 1987), research has been limited on this fatty acid. Recently, Rahman et al. (1994) developed a mutant (M23) with about 500 g kg-1 oleic acid. Takagi and Rahman (1996) first observed that the oleic acid content in this mutant was controlled by a single recessive allele, designated as ol. Another allele ola at the same Ol locus was found in mutant M11 that contains about 380 g kg-1 oleic acid (Rahman et al., 1996a).

Soybean germplasms with a low content of linolenic acid were developed from treatment with x-rays or chemical mutagens and further hybridization of mutants (Takagi et al., 1990; Fehr et al., 1992; Rahman and Takagi, 1997; Rahman et al., 1998). Inheritance studies showed that low linolenic acid was controlled by either a single locus or two loci. The single locus fan was found in C1640 (Wilcox and Cavins, 1985); PI 361088B (Rennie et al., 1988); PI 123440 (Rennie and Tanner, 1989); A5 (Rennie and Tanner, 1991); and M-5 (Rahman et al., 1996b). Fan2 was found in A23 (Fehr et al., 1992); fanx in KL-8 (Rahman and Takagi, 1997); and fanxa in M-24 (Rahman et al., 1998). Evidence of two loci were found in A16 and A17 (fanfan2, Fehr et al., 1992); MOLL (fanfanx, Rahman and Takagi, 1997); and LOLL (fanfanxa, Rahman et al., 1998). The germplasms A16, A17, and LOLL contain 250 to 280 g kg-1 linolenic acid, which is the lowest reported in soybean oil.

The genetic relationship of the loci for high oleic and low linolenic acids in soybean is still unknown, although studies on relationships of low linolenic acid with low and high palmitic acid in soybean (Nickell et al., 1991), and with high palmitic acid in flax (Linum usitatissimum L.) (Ntiamoah et al., 1995), were conducted and soybean and flax cultivars were successfully developed. If the loci for high oleic and low linolenic acids are independently inherited, a soybean cultivar with desired contents of these fatty acids can easily be developed, and this oil will have high nutritional value. Therefore, this investigation was undertaken to combine the loci of high oleic and low linolenic acids, and determine if changes in contents of oleic and linolenic acids would affect contents of other fatty acids in these genetic systems.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
The recombinant lines HOLL and LOLL were used for the present study. The line HOLL is a high oleic and low linolenic acid selection from the cross M23 x M-5. LOLL is a very low linolenic acid selection from the cross M-5 x M-24. The fatty acid composition and genotype of HOLL, LOLL, their parental lines, and the original cultivar Bay (Takagi et al., 1990) are shown in Table 1.


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  		Table 1. Average (± SE) fatty acid composition and genotype of the original cultivar (Bay) and the soybean lines selected for high oleic or low linolenic acids

 
The lines HOLL and LOLL were reciprocally crossed in the glasshouse at Saga University. Seed of parents and reciprocal F1 seed was planted in the field in August 1997. Each of the parent and F1 plants were harvested individually. To reduce the environmental effects on fatty acid composition, seed of parents and F2 seed of each F1 plant were collected from pods of similar maturity on the fifth to seventh nodes of the main stem. Fatty acid composition was determined from 48 F2 seeds of each reciprocal cross and 20 seeds of each parent. The F2 seed was cut into two parts with a razor blade. The portion containing the embryonic axis was stored, and the portion containing a section of the cotyledon was used for fatty acid analysis. The identity of all F2 seed was maintained during fatty acid analysis.

The range of oleic and linolenic acid contents of the parents grown in the same field conditions with the F1 plants were used to classify the F2 seed. An F2 seed was considered similar to the parent when its fatty acid content was within the range exhibited by that parental seed. Thus, for oleic acid, the F2 seed was classified as =LOLL, >LOLL to <HOLL, and =HOLL. For linolenic acid, the F2 seed was classified as =HOLL, <HOLL to >LOLL, and =LOLL. This classification was also used to evaluate segregation of oleic and linolenic acids combined.

Four F2 seeds, with oleic acid similar to HOLL and linolenic acid similar to LOLL, were identified. These F2 seeds and four seeds from each of HOLL, LOLL, and Bay were planted in the field in 1998, and the plants were harvested individually. Ten individual F3 seeds from each F2 plant, and from four plants in each of HOLL, LOLL, and Bay, were analyzed for fatty acid composition.

Fatty acid composition was determined by gas chromatography, as described by Takagi et al. (1989). Chi-square analyses were calculated to test the best fit of data to expected genetic ratios. A single gene model was used to evaluate the segregation ratio for oleic and linolenic acids individually in F2 seed, while a two-gene model was applied for the evaluation of these two fatty acids combined.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Data from reciprocal F2 seed of the HOLL x LOLL cross were analyzed for the ol and fanxa loci individually to determine if the data were similar with results previously reported for these loci. Data from reciprocal F2 seed were combined because their {chi}2 values were homogeneous for both oleic and linolenic acid content. Trimodal frequency distribution patterns for both oleic and linolenic acids were evident from the combined data (Fig. 1 and Fig. 2) . The data for oleic acid were 25 OlOl:49 Olol:22 olol (Fig. 1) that resulted in a {chi}2 value of 0.23 (P > 0.90) indicating a satisfactory fit to the 1:2:1 ratio (Table 2). This single gene inheritance of the oleic acid trait in HOLL is supported by the results of genetic system of ol in its parent M23 (Takagi and Rahman, 1996). Since both HOLL and LOLL possess the fan (M-5) locus, only the fanxa (M-24) locus for linolenic acid in LOLL will participate in the segregation of F2 seed in the HOLL x LOLL cross. Therefore, the combined data for linolenic acid produced a ratio of 23 fanfanFanxFanx:51 fanfanFanxfanxa:22 fanfanfanxafanxa (Fig. 2), with a {chi}2 value of 0.14 (P > 0.90) indicating also a good fit to the expected 1:2:1 ratio (Table 2), which is consistent with previous results (Rahman et al., 1998).



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  		Fig. 1. Distribution of oleic acid content in soybean seed of LOLL and HOLL and in F2 seed of LOLL x HOLL cross

 


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  		Fig. 2. Distribution of linolenic acid content in soybean seed of LOLL and HOLL and in F2 seed of LOLL x HOLL cross

 

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  		Table 2. Chi-square ({chi}2) analyses of oleic and linolenic acid contents individually and combined in F2 soybean seeds of LOLL x HOLL cross

 
For two fatty acids combined, two loci (ol for the high oleic acid trait and fanxa for the low linolenic acid trait) are expected to segregate in the HOLL x LOLL cross. Because both the ol locus in HOLL and fanxa locus in LOLL segregate to a 1:2:1 ratio, segregation for these two individual loci with additive effects should result in a ratio of 1:2:1:2:4:2:1:2:1 for contents of the two fatty acids. Nine phenotypic classes were observed (Fig. 3) , and the combined data for these fatty acids gave a consistent good fit to the expected ratio ({chi}2 = 1.54; P > 0.99; Table 2).



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  		Fig. 3. Scatter graph of oleic acid vs. linolenic acid in oil from F2 soybean seed of LOLL x HOLL cross

 
There were four F2 plants with the genotype ololfanfanfanxafanxa, on the basis of the progeny test. The mean oleic acid content in 40 F3 seeds of these plants (DHL) was 563 g kg-1, compared with 544 g kg-1 for HOLL, 339 g kg-1 for LOLL, and 344 g kg-1 for Bay (Table 3). The mean linolenic acid content in DHL was 28 g kg-1, compared with 42 g kg-1 for HOLL, 29 g kg-1 for LOLL, and 78 g kg-1 for Bay. These results also support a three-locus model in which ol locus is responsible for 563 g kg-1 oleic acid (Takagi and Rahman, 1996), and fan and fanxa loci are responsible for 28 g kg-1 linolenic acid (Rahman et al., 1998) in the segregant DHL.


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  		Table 3. Average (± SE) fatty acid composition of the original cultivar (Bay) and the soybean lines for high oleic or low linolenic acids

 
The elevation of oleic acid contents from 334 to 544 and 563 g kg-1 in HOLL and DHL respectively, did not appear to be associated with changes in palmitic and stearic acids (Table 3). The linolenic acid contents in HOLL and DHL can not be associated with a change in oleic acid as the former one is controlled by either the fan locus or in combination with the fanxa locus. The most consistent association was a remarkable decrease in the mean linoleic acid content with each increase in the mean oleic acid content. This inverse association of oleic and linoleic acid contents strongly suggests a pleiotropic effect of the ol locus in HOLL and DHL. Similar associations in the contents of these two fatty acids have been identified in safflower (Carthamus tinctorius L.) and sunflower (Helianthus annuus L.), also normally having lines with low oleic and high linoleic acid contents (Knowles and Hill, 1964; Downey and Dorrell, 1971). In maize (Zea mays L.), the 200 g kg-1 difference in oleic and linoleic acid contents was controlled by a single gene, the ln locus with high oleic acid content being dominant to low (de la Roche et al., 1971). Thus, it is apparent that the decreased linoleic acid content was a direct consequence of the increased content of its precursor, oleic acid. Conversely, effects of low linolenic acid content on the other fatty acids showed that the 48 g kg-1 reduction of linolenic acid content from 78 to 29 g kg-1 in LOLL was directly associated only with a 45 g kg-1 increase in linoleic acid. The oleic and linoleic acid contents in DHL can not be associated with a change in linolenic acid as the former two fatty acids are controlled by ol locus. The contents of palmitic and stearic acids remained unchanged.

Because the high oleic acid trait of HOLL and the very low linolenic acid trait of LOLL are under simple Mendelian inheritance, the germplasm DHL was easily developed. Such a germplasm could change the total dependence on oils with high oleic acid and ensure the desirable flavor stability of an oil. Investigations into the effects of the mutant alleles on yield and other agronomic traits in DHL are under way.

Received for publication November 15, 1999.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 




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