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Oil Crops Research Institute, Guizhou University, Guiyang 550025, China

Abstract　In order to screen and identify excellent breeding resources and provide basic materials for Brassica rapa breeding, the contents of erucic acid, oleic acid and glucosinolate in 84 kinds of B. rapa were determined by near-infrared spectroscopy, and the correlations among them were also analyzed. The results showed that the content of erucic acid and oleic acid were significantly negatively correlated, the contents of erucic acid and glucosinolate were significantly positively correlated, while the contents of oleic acid and glucosinolate were significantly negatively correlated; principal component analysis (PCA) were performed on the population materials, factors 1 and 2 were extracted for plotting, factor 1 and factor 2 could explain 73.7% and 23.2% of the phenotypic variation, respectively; through cluster analysis, 79 materials aggregated to form group I, and five special variants deviated from the population. The variation of erucic acid, oleic acid and glucosinolates in B. rapa populations was rich and there was significant correlation. Through cluster analysis, five excellent B. rapa breeding materials (No. 32, No. 45, No. 46, No. 50, and No. 59) were screened.

Key words　Brassica rapa, Erucic acid, Oleic acid, Glucosinolate

1　Introduction

Brassicanapus(AACC, 2n= 38),Brassicajuncea(AABB, 2n= 36) andBrassicarapa(AA, 2n= 20) are three largest genusBrassicaoil crops[1], of whichB.napushas important characteristics such as short growing period, suitable for spring sowing and oil pressing and being used as vegetable. China is an important origin ofB.rapawhich has abundant germplasm resources. It is of great significance to strengthen the research of theory and application ofB.rapato increase the supply of vegetables in urban and rural areas and to ensure the safety of oil in China. Before the introduction ofB.napus,B.rapawas the main oil crop in China. However, due to low quality traits ofB.rapa(high erucic acid, high glucosinolates, and low oleic acid), the yield was low,B.rapawas gradually replaced byB.napus. Erucic acid affects the quality of oil, and much taking of erucic acid may cause damage to the human myocardial fibers, development, and fertility[2]. China has regulated the erucic acid content of the newB.napusvarieties to ≤ 5% (agricultural industry standard NY/T415-2000). Oleic acid, as a monounsaturated fatty acid, has the effects of lowering cholesterol, blood sugar, and ester density[3]. The glucosinolate is the anti-nutritional factor of rape seeds, and China specifies that the erucic acid content of newB.napusvarieties is ≤ 45 μmol/g (agricultural industry standard NY/T415-2000). The glucosinolates are related to the plant’s self-protection mechanism, and glucosinolates and their hydrolysates are essential parts of the plant defense system[3]. Therefore, reducing erucic acid and glucosinolate content and increasing oleic acid content are important goals for quality breeding of rape seed[5-6]. Due to unique characteristics,B.rapacan be used as a beneficial supplement for the production ofB.napusafter genetic improvement of quality traits and some agronomic traits. In the world, the germplasm resources ofB.rapawith low erucic acid, low glucosinolates and high oleic acid are relatively limited, which limits the development ofB.rapabreeding. In order to strengthen the selection and cultivation of excellentB.raparesources, we selected 84B.rapaseed resources and planted and measured the erucic acid, oleic acid and total glucosinolates in the ecological environment of Guiyang. It is expected to screen potentialB.rapaspecific breeding materials, so as to provide germplasm basis for genetic breeding and basic research ofB.rapa.

2　Materials and methods

2.1ExperimentalmaterialsWe selected 84 kinds ofB.rapagermplasm resources (Table 1), planted at the teaching practice site of Guizhou University in October 2014, and each material was sown with two rows. At the flowering stage, three single plant were randomly selected, bagged and self crossed, and their seeds were collected.

2.2MeasurementindicatorsandmethodsFor each material, 3 g plump seeds were selected, and near-infrared spectroscopy was applied to determine the erucic acid, oleic acid and glucosinolate content of seeds. Repeated two times and calculated the average value for data analysis.

2.3StatisticalanalysisFor the data obtained, SPSS20 software was used for statistical analysis, and correlation and principal component analysis (PCA) were performed.

Table 1　Number, name and origin of experimental materials

3　Results and analysis

3.1TraitvariationinthepopulationThe 84 varieties ofB.rapagermplasm resources from all areas of China were rich in erucic acid, oleic acid and glucosinolates under Guiyang environmental conditions and all showed a normal distribution (Fig.1). As can be seen from Table 2, the average erucic acid content of the 84B.rapagermplasm resources was 49.7% and the coefficient of variation was 12.7%. Among them, No. 59 material had the lowest erucic acid content, which was 21.2%; No. 48 material had the highest erucic acid content, which was 59.4%. The average oleic acid content was 11.6%, and the coefficient of variation was 67.2%. Among them, No. 84 material had the lowest oleic acid content (2.4%); No. 59 material had the highest content (61.0%). The average glucosinolate content was 119.1 μmol/g and the coefficient of variation was 16.5%. Among them, the glucosinolate content of No. 50 material was the highest, which was 193.6 μmol/g; the thioglycoside content of No. 59 material was the lowest, which was 50.9 μmol/g.

3.2Correlationofoleicacid,erucicacidandtotalglucosinolatecontentsThe correlation analysis of oleic acid, erucic acid, and glucosinolate contents in 84B.rapapopulations showed that the erucic acid content was significantly negatively correlated with the oleic acid content (R= -0.906**), and was significantly positively correlated with the glucosinolate content (R= 0.426**); the oleic acid was significantly negatively correlated with glucosinolate content (R= -0.431**). During the selection and breeding ofB.rapavarieties, it is required to pay attention to the screening of high glucosinolates (corresponding to high erucic acid) and low glucosinolates (corresponding to high erucic acid and high oleic acid).

3.3Populationclusteringandspecificmaterialscreening

3.3.1Principal component analysis (PCA). The principal component analysis showed that PCA1 and PCA2 could explain the population phenotypic variation of 96.9% in total, and PCA1 accounted for 73.7% of the phenotypic variation of the population, while PCA2 could explain 23.2% of the phenotypic variation of the population material. This indicates that there are two principal component factors in the traits studied, and the clustering results are more accurate and can represent most of the traits.

Fig.1Thecontentoferucicacid,oleicacidandglucosinolatesofBrassicarapagermplasmresources

Table 2　Variation of erucic acid, oleic acid and glucosinolate contents in Brassica rapa populations

3.3.2Specific material screening. The clustering results showed that 79 pieces ofB.rapamaterial aggregated to form group I, and another five pieces (No. 32, No. 45, No. 46, No. 50, and No. 59) materials deviated from the population were specific materials. The average erucic acid content of the specific material population was 50.6%, the coefficient of variation was 8.5%, the minimum erucic acid content was 41.2%, and the maximum erucic acid content was 59.4%. The average oleic acid content was 10.4%, the coefficient of variation was 39.4%, the minimum oleic acid content was 2.4%, and the maximum oleic acid content was 22.0%. The average glucosinolate content was 118.6 μmol/g and the coefficient of variation was 12.7%. The highest glucosinolate content was 149.6 μmol/g, and the lowest glucosinolate content was 79.0 μmol/g.

3.3.3The erucic acid, oleic acid and glucosinolate contents of specific materials. The erucic acid, oleic acid, and glucosinolate contents of No. 32 material were 47.5%, 12.4%, and 162.3 μmol/g, respectively, having variations of -6%, 19%, and 37%, respectively, compared with the average value of group I. The erucic acid, oleic acid, and glucosinolate contents of No. 45 material were 28.5%, 35.2%, and 76.7 μmol/g, respectively, having variations of -44%, 239%, and 35%, respectively, compared with the average value of group I. The erucic acid, oleic acid, and glucosinolate contents of No. 46 material were 26.9%, 35.0%, and 147.3 μmol/g, respectively, having variations of -47%, 237%, and 24%, respectively, compared with the average value of group I. The erucic acid, oleic acid, and glucosinolate contents of No. 50 material were 55.2%, 8.9%, and 193.6 μmol/g, respectively, having variations of 9%, -14%, and 63%, respectively, compared with the average value of group I. The erucic acid, oleic acid, and glucosinolate contents of No. 59 material were 21.2%, 61.0%, and 50.9 μmol/g, respectively, having variations of -58%, 487%, and -57%, respectively, compared with the average value of group I.

4　Conclusions and discussions

The genetic variation of the importance of oil crop germplasm resources is of great significance for mining excellent materials of oil crops[7-9]. The same genotype material may have different performance under different environmental conditions, including temperature, altitude, light, foliar fertilizer and soil fertility[10-13]. In the ecological environment of Guiyang, we selected 84B.rapaseed resources and planted and measured the erucic acid, oleic acid and total glucosinolates. Through the analysis of quality traits, it was found that these materials showed wide variation in the contents of erucic acid, oleic acid, and glucosinolates, and five excellent germplasm resources of No. 32, No. 45, No. 46, No. 50, and No. 59 were screened, so as to provide germplasm basis for genetic breeding and basic research ofB.rapa.

There are few studies on the correlation between erucic acid, oleic acid and glucosinolate quality traits inB.rapa. InB.napus, Zhu Zonghe[14]performed a correlation analysis of the quality traits in the F2generation of 165 hybrid combinations, indicating that the erucic acid and oleic acid content were extremely significantly negatively correlated. Wang Jiansheng[15]found that the erucic acid and glucosinolate contents ofB.napuswere significantly positively correlated. Liu Houlietal.[16-17]showed that there was a highly significant negative correlation between erucic acid and oleic acid content, and there was an extremely significant positive correlation between erucic acid content and glucosinolate content, and there was an extremely significant negative correlation between oleic acid and glucosinolate content. These results are consistent with the conclusions obtained in this study. China is an important origin ofB.rapaand its germplasm resources are relatively abundant, but there are relatively few germplasm resources ofB.rapawith low erucic acid, high oleic acid, low glucosinolate content and specific quality. Therefore, this study is expected to provide a certain reference value forB.rapabreeding and its basic research.