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1. Hunan Academy of Forestry, Changsha 410004, China; 2. National Engineering Research Center for Oiltea Camellia, Changsha 410004, China; 3. Shaoyang County Forestry Bureau, Shaoyang 422100, China

Abstract This paper studied effects of different picking time and different geographical provenances on oil content of Camellia oleifera. The results showed that different picking time had significant effects on the oil content of cold dew seeds and frost’s descent seeds. With the delay of picking time, the oil content of cold dew seeds, frost’s descent seeds, dry seeds and oil content of seed kernels were significantly increased. There was a significantly positive correlation between the oil content of fresh fruit of cold dew seeds and frost’s descent seeds and the dry seed yield of fresh seeds and the oil content of fresh fruit (P<0.05), and the correlation coefficient was greater than 0.85. Besides, the oil content of seed kernels of cold dew seeds was closely correlated with the seed yield of fresh seeds, oil content of fresh fruit, and oil content of fresh seeds. In the process of C. oleifera breeding, the thin coat, high seed yield and high oil content can be taken as the key research directions for future breeding. The oil content of ordinary C. oleifera seeds in 18 counties (cities) was 36.42%-63.33%, indicating that there were significant differences in the oil content of C. oleifera in different geographical provenances. In conclusion, according to the study of different picking time, the recommended picking time of cold dew seeds in Hunan area is around October 10, while the best picking time of frost’s descent seeds is about October 30. The oil content of C. oleifera fruit in different geographical provenances is quite different. During the development of C. oleifera fruit, the cultivation and management of C. oleifera should be strengthened to increase the oil content of C. oleifera.

Key words Camellia oleifera, Picking time, Geographical provenances, Oil content

1 Introduction

Camelliaoleiferais an important woody oil tree species unique to China, mainly distributed in the provinces south of the Yangtze River. Together withElaeisguineensis,Oleaeuropaea, andCocosnucifera,C.oleiferais one of the four largest woody oil tree species in the world, and it reputed as the Oriental Olive Oil[1]. Camellia oil has a unique edible value and health value, and thus is favored by people. The oil content ofC.oleiferais usually used as an essential indicator to measure the yield ofC.oleiferaand the variety ofC.oleifera[1]. Therefore, study of oil content ofC.oleiferais of great significance. About the oil content, scholars have carried out extensive studies and have made certain achievements. Xi Ruchunetal.[1]found that there was a extremely significant correlation between the oil yield ofC.oleiferaa and oil content of fresh fruit and the oil content of seed kernels. According to the study of 44 excellent strains ofC.oleiferaby Wang Xiangnanetal.[2], the oil content of different strains ofC.oleiferawas significantly different, and there was a certain correlation between the oil content of dry seeds, and the latitude and altitude. Gao Weietal.[3]found that the oil content ofC.oleiferaseeds has a significant correlation with harvesting methods and varieties. Luo Fanetal.[4]studied the effects of picking time on the quality ofC.oleiferaoil, and found that with the gradual maturity ofC.oleiferaseeds, the content of unsaturated fatty acids in oil increased. According to the study of Chen Yangetal.[5], there are significant differences in the oil content of between ordinaryC.oleifera,CamelliareticulataandCamelliachekiangoleosa. According to the study of Zhu Yongetal.[6], the oil content ofCamelliasemiserrataseed kernel is 60%, the oil content ofCamelliafangchengensisand ordinaryC.oleiferais 50%, the oil content ofCamelliagigantocarpaand Vietnam’sCamelliavietnamensisis 40%, and the oil content is significantly different in different species ofC.oleifera.

At present, there is a big gap between China’sC.oleiferaoil production and people’s actual demand, and it is still impossible to achieve consumption by the whole people. Actively breeding new varieties and increasingC.oleiferaoil production has become an important research direction for the development of theC.oleiferaindustry[3]. In view of this, we analyzed effects of different picking time and different geographical provenances on oil content ofC.oleifera, to find factors influencing the oil content ofC.oleiferaand further provide certain references for breeding of new varieties of high oil contentC.oleiferavarieties.

2 Materials and methods

2.1ExperimentalmaterialsIn mid-October 2017, we collected the mature fruits ofC.oleiferavarieties in 18 counties (cities) of Hunan Province, and carried out experimental study on the oil content of ordinaryC.oleiferain different geographical provenances. The areas of samples cover all producing areas ofC.oleiferain Hunan Province. In each collection site, we randomly selected fiveC.oleiferatrees and picked the fruit in accordance with the criterion of slightly crackingC.oleiferafruit. After picking, we peeled off the seeds, naturally dried, peeled off seed shells and seed kernels, crushed seed kernels, screened with 40-mesh sieve, and placed and sealed in a -20℃ refrigerator for subsequent experiment.

The experimental materials (cold dew seeds) came from Tianjiling Experimental Forest Farm of Hunan Academy of Forestry (113.04° N, 28.12° E) and the Lukou Town Base of Changsha County (113.22° N, 28.41° E). With the subtropical monsoon climate, experiment site has four distinct seasons throughout the year, abundant rainfall, mild climate, abundant sunshine and heat, and rainy and hot days come in the same season. It has typical north-south transitional climate characteristics. The elevation is in the range of 50-75 m. The soil is acidic. After the fruit was grown and shaped fixed, we selected sample plants in the late August, and selected 10 plants separately for the cold dew and the frost’s descent seeds. The selection criterion for the sample plants is robust growth, no pests and diseases, and the yield of the current year is above 2.5 kg/plant. The sampling time of the cold dew seeds took the Cold Dew Day as the center, starting from September 26 and ending on October 10. The sampling time of the frost’s descent seeds started from October 11 and ended on October 30. The sampling was carried out at 9:00-12:00, one time every 2-3 d. Each time, 20-30 fruits were picked from each plant. After picking, we peeled off the seeds, naturally dried, peeled off seed shells and seed kernels, crushed seed kernels, and placed and sealed in a -20℃ refrigerator for subsequent experiment.

2.2ExperimentmethodsThe oil content of the seed kernels was determined by Soxhlet extraction method. Precisely weighed 5 g of the samples and placed in the filter paper tube, then placed the filter paper tube into the extraction tube of the fat extractor, connected the receiving flask dried to constant weight, added petroleum ether to 2/3 of the volume from condensing tube of the extractor, heated on the water bath to allow the petroleum ether to be continuously refluxed for extraction for 6 h. After completion of the extraction, remove the receiving flask, recovered the petroleum ether. When the petroleum ether in the flask was 1-2 mL, evaporated to dryness on a water bath, dried at 100℃ for 2 h, and then cooled in a desiccator for 0.5 h, and then weighed. Repeated the above operation till the weight was constant.

The formula for oil content:X= (M1-M0)/M2×100

whereXdenotes the fat content in the sample, expressed in g/100g;M1denotes the fat content after constant weight, expressed in g;M0denotes the mass of the receiving flask, expressed in g;M2denotes the mass of the sample, expressed in g.

2.3DataprocessingWe conducted calculation and analysis of data with the aid of software Excel and SPSS16.0.

3 Results and analysis

3.1EffectsofpickingtimeonoilcontentofC.oleiferaWith the delay of picking time, the oil content of both dry seeds of cold dew seeds and seed kernels was significantly increased (Table 1). The kernel yield of dry seeds ofC.oleiferafruits picked on September 26 was 55.26%, while the kernel yield of dry seeds ofC.oleiferafruits picked on October 10 was 58.50%, increasing by 3.24%. The oil content of dry seeds ofC.oleiferafruits picked on September 26 was 12.14%, while the oil content of dry seeds ofC.oleiferafruits picked on October 10 was 19.34%, increasing by 7.20%. Accordingly, the oil content of seed kernels ofC.oleiferafruits picked on September 26 was 21.96%, while the oil content of seed kernels ofC.oleiferafruits picked on October 10 was 33.06%, increasing by 11.10%.

Table1OilcontentofcolddewseedsofCamelliaoleiferapickedindifferenttime%

The oil content is generally taken as an essential indicator for measuring economic trait and edible value ofC.oleifera. With the delay of picking time, the oil content of both dry seeds of cold dew seeds and seed kernels was significantly increased (Table 2). The oil content of dry seeds ofC.oleiferafruits picked on October 11 was 18.48%, while the oil content of dry seeds ofC.oleiferafruits picked on October 30 was 25.22%, increasing by 6.74%. Accordingly, the oil content of seed kernels ofC.oleiferafruits picked on October 11 was 32.35%, while the oil content of seed kernels ofC.oleiferafruits picked on October 30 was 43.09%, increasing by 10.74%. The kernel yield of dry seeds ofC.oleiferafruits picked on October 11 was 57.10%. The kernel yield of dry seeds ofC.oleiferafruits picked on October 30 was 58.52%, increasing by 1.42%.

In summary, for both the cold dew seeds and frost’s descent seeds, the oil content of dry seeds, the oil content of seed kernels, and kernel yield of dry seeds were increasing with the delay of picking time. This indicates that the picking time has an significant effect on the oil content ofC.oleifera. In terms of the coefficient of variation, the kernel yield, dry seed oil content, and seed kernel oil content of frost’s descent seeds were 0.03, 0.10, and 0.10, respectively, while the kernel yield, dry seed oil content, and seed kernel oil content of cold dew seeds were 0.06, 0.24, and 0.18, respectively. By contrast, the effects of picking time on the kernel yield and oil content of cold dew seeds were more significant. Therefore, determining proper picking time has great significance for increasing the kernel yield and oil content ofC.oleiferafruit.

Table2Oilcontentoffrost’sdescentseedsofCamelliaoleiferapickedindifferenttime%

Picking time Kernel yield ofdry seedsOil content ofdry seedsOil content ofseed kernelOct. 11, 201757.10 18.48 32.35Oct. 13, 201761.35 20.45 33.33Oct. 16, 201761.25 22.46 36.67Oct. 18, 201760.79 22.10 36.35Oct. 24, 201760.60 23.23 38.34Oct. 27, 201757.85 22.37 38.67Oct. 30, 201758.52 25.22 43.09Max.61.35 25.22 43.09Min. 57.10 18.48 32.35Average value59.64 22.04 36.97Standard deviation1.76 2.12 3.59Coefficient of variation0.03 0.10 0.10

3.2CorrelationanalysisofoilcontentofC.oleiferaIn terms of the coefficient correlation of cold dew seeds (Table 3), the oil content of fresh fruits was significantly positively correlated with the dry seed yield of fresh seeds, the correlation coefficient was 0.969 (P<0.01), the oil content of fresh seeds was also significantly positively correlated with the oil content of fresh fruit and dry seed yield of fresh seeds, and the correlation degree was oil content of fresh seeds > oil content of fresh fruit. The oil content of dry seeds was significantly positively correlated with dry seed yield of fresh seeds, oil content of fresh fruit, and oil content of fresh seeds, and correlation degree was oil content of fresh seeds > oil content of fresh fruit > dry seed yield of fresh seeds. The oil content of seed kernel was significantly positively correlated with dry seed yield of fresh seeds, oil content of fresh fruit, oil content of fresh seeds, and oil content of dry seeds, and correlation degree was oil content of dry seeds > oil content of fresh seeds > oil content of fresh fruit > dry seed yield of fresh seeds. In terms of the correlation of frost’s descent seed indicators (Table 4), the oil content of fresh fruits was significantly positively correlated with the dry seed yield of fresh seeds, the oil content of fresh seeds was significantly positively correlated with the oil content of fresh fruits, and the oil content of seed kernel was significantly positively correlated with the oil content of dry seeds.

By contrast, for both the cold dew seeds and frost’s descent seeds, there was a significant correlation between the oil content of fresh fruit and dry seed yield of fresh seeds. The oil content of fresh seeds and oil content of seed kernel of frost’s descent seeds were significantly positively correlated with the oil content of fresh fruit and oil content of dry seeds, while the oil content of fresh seeds of cold dew seeds was significantly positively correlated with the oil content of fresh fruit and the dry seed yield of fresh seeds. The oil content of seed kernel of frost’s descent seeds was significantly positively correlated with the oil content of dry seeds, the dry seed yield of fresh seeds, the oil content of fresh fruit, and the oil content of fresh seeds. In addition, the oil content of dry seeds of cold dew seeds was significantly positively correlated with the oil content of dry seeds, the dry seed yield of fresh seeds, the oil content of fresh fruit, and the oil content of fresh seeds, while the oil content of dry cold dew seeds showed no significant correlation with all these indicators (P>0.05).

Table3CorrelationanalysisofoilcontentindicatorofcolddewseedsofCamelliaoleifera%

Fresh seed yieldof fresh fruitDry seed yield offresh seedsKernel yield ofdry seedsOil content offresh fruitOil content offresh seedsOil content ofdry seedsOil content ofseed kernelFresh seed yield of fresh fruit1.000 - - - - --Dry seed yield of fresh seeds-0.0421.000 - - - --Kernel yield of dry seeds0.1320.6761.000 - - --Oil content of fresh fruit-0.1580.969**0.7611.000 - --Oil content of fresh seeds-0.2940.944**0.7180.990**1.000 --Oil content of dry seeds-0.3290.927**0.7170.984**0.999**1.000-Oil content of seed kernel-0.5020.853*0.3970.880*0.922**0.924**1.000

Note:**denotesP<0.01, while*denotesP<0.05, the same in Table 4.

Table4Correlationanalysisofoilcontentindicatoroffrost’sdescentseedsofCamelliaoleifera%

Fresh seed yieldof fresh fruitDry seed yield offresh seedsKernel yield ofdry seedsOil content offresh fruitOil content offresh seedsOil content ofdry seedsOil content ofseed kernelFresh seed yield of fresh fruit1.000 - - - - --Dry seed yield of fresh seeds0.3671.000 - - - --Kernel yield of dry seeds-0.0130.2951.000 - - --Oil content of fresh fruit0.6710.850*0.2011.000 - --Oil content of fresh seeds0.1600.844*0.2580.839*1.000 --Oil content of dry seeds-0.1330.2590.1810.4590.7331.000-Oil content of seed kernel-0.1200.191-0.1130.4190.6760.957**1.000

3.3DifferencesofoilcontentrelatedtraitsofordinaryC.oleiferaindifferentregionsAccording to the data in Table 5, there was significant difference in the seed yield and oil content of ordinaryC.oleiferaproduced in different regions. The seed yield of fresh fruit showed a variation in the range of 35.20%-50.26% and the coefficient of variation was 0.10. One county (city) had the seed yield of fresh fruit higher than 50%, 14 counties (cities) in the range of 40%-50%, and three counties (cities) in the range of 40%-50%. The dry seed yield of fresh seeds showed a variation in the range of 40.39%-57.12% and the coefficient of variation was 0.11. Eight counties (cities) had dry seed yield of fresh seeds higher than 50%, and ten counties (cities) in the range of 40%-50%. The kernel yield of dry seeds showed a variation in the range of 51.40%-63.96% and the coefficient of variation was 0.08, and 18 counties (cities) had kernel yield of dry seeds of ordinaryC.oleiferahigher than 50%.

The oil content of fresh fruit had a variation in the range of 3.53%-9.37%, the coefficient of variation was 0.26, and the average value was 5.39%. The oil content of fresh seeds had a variation in the range of 8.16%-21.23%, the coefficient of variation was 0.27, and the average value was 12.34%. The oil content of dry seeds had a variation in the range of 18.93%-37.51%, the coefficient of variation was 0.19, and the average value was 25.18%. Two counties (cities) had the oil content of dry seeds higher than 30%, 15 counties (cities) in the range of 20%-30%, and one county (city) below 20%. The oil content of seed kernel had significant difference, the variation range was 36.42%-63.33%, the coefficient of variation was 0.14, and the average value was 43.58%. One county (city) had the oil content of seed kernel higher than 50%, 12 counties (cities) in the range of 40%-50%, and five counties (cities) below 40%.

The above data indicated that the oil content related indicators of ordinaryC.oleiferaproduced in 18 counties (cities) had significant differences, and the difference of oil content of seed kernel was 26.91%.

Table5AnalysisofoilcontentofCamelliaoleiferaproducedindifferentgeographicalprovenances%

Sample source Seed yield offresh fruit Dry seed yield offresh seedsKernel yield ofdry seedsOil content offresh fruitOil content offresh seedsOil content ofdry seedsOil content ofseed kernelLLS45.73 43.74 52.86 4.35 9.52 21.70 41.00CLX48.02 51.79 55.99 6.31 13.15 25.38 45.33HDX46.87 44.47 51.43 4.26 9.20 20.15 38.40LYS41.93 57.12 59.56 6.56 15.64 27.37 46.17CNS46.59 50.33 51.40 4.95 10.62 21.10 41.04PJX35.44 44.71 63.96 4.12 11.63 26.01 40.67MLS50.26 44.28 52.12 4.22 8.40 18.98 36.42XPX47.63 40.39 52.79 3.91 8.21 20.33 38.51SNX35.20 44.05 63.88 4.89 13.88 31.51 49.33ZFX48.89 41.97 60.93 4.64 9.48 22.60 37.08YZX47.38 51.88 61.92 6.10 12.97 25.06 40.46ZXS44.15 56.59 59.22 9.37 21.23 37.51 63.33SYX36.56 53.16 59.44 5.40 15.56 28.05 46.96DX48.19 47.72 61.35 5.92 12.29 25.77 42.00NYX41.82 49.64 56.39 5.61 13.04 26.03 46.13QYX43.37 51.07 58.13 6.01 13.85 27.13 46.67DAX43.32 40.77 51.75 3.53 8.16 20.01 38.67YZS45.17 53.21 61.34 6.91 15.26 28.50 46.34Max.50.26 57.12 63.96 9.37 21.23 37.51 63.33Min. 35.20 40.39 51.40 3.53 8.16 18.98 36.42Average value44.25 48.16 57.47 5.39 12.34 25.18 43.58Standard deviation4.57 5.28 4.46 1.41 3.38 4.67 6.29Coefficient of variation0.10 0.11 0.08 0.26 0.27 0.19 0.14

4 Conclusions and discussions

The picking time has a significant effect on the oil content ofC.oleifera. Improper picking time may cause a certain loss to the overall yield ofC.oleifera[8]. Through this study, we found that during September 26 and October 4, for the cold dew seeds, the oil content of dry seeds and the oil content of seed kernel increased slowly, while during October 4 and October 10, the oil content of dry seeds and the oil content of seed kernel increased rapidly. For the frost’s descent seeds, the trend of changes in the oil content was similar: during October 11 and October 27, the oil content of dry seeds and the oil content of seed kernel increased slowly, while during October 27 and October 30, the oil content of dry seeds and the oil content of seed kernel increased rapidly, increasing by 2.85% and 4.42%, respectively. This is consistent with the existing research results, and the oil content shows a trend of "stable increase-sharp increase-decline"[7-9]. The slow growth of oil content is the stage of oil conversion, indicating that the nutrient and oil synthesis precursors inC.oleiferaseeds are in the process of storage at this stage. When these substances reach a certain amount, they can enter the oil conversion stage[6], correspondingly, during this stage, the oil content also increased. Generally, determining the proper picking time is important for increasingC.oleiferayield[8]. Therefore, based on the analysis of different picking time, the recommended picking time of cold dew seeds in Hunan area is around October 10, while the best picking time of frost’s descent seeds is about October 30.

Apart from the picking time, there are many factors influencing the oil content ofC.oleifera[2]. Through the analysis, we found that for both the cold dew seeds and frost’s descent seeds, there is a significantly positive correlation between the oil content of fresh fruit and dry seed yield of fresh seeds, the coefficient of correlation is 0.969 (P<0.01) and 0.850 (P<0.05), the correlation is higher between the oil content of fresh fruit and dry seed yield of fresh seeds for cold dew seeds. Besides, for both the cold dew seeds and frost’s descent seeds, there is a significantly positive correlation between the oil content of fresh seeds and the oil content of fresh fruit, and the correlation is higher between the oil content of fresh seeds and the oil content of fresh fruit. This is mainly because the fruit of the cold dew seeds is small and the coat is thin, while the fruit of the ordinaryC.oleiferais large and the fruit is thick[8]. For both the cold dew seeds and frost’s descent seeds, the oil content of seed kernel is significantly positive correlated with the oil content of dry seeds (P<0.05), and the oil content of seed kernel of cold dew seeds is also closely correlated with the dry seed yield of fresh seeds, the oil content of fresh fruit, and the oil content of fresh seeds. Therefore, in the process ofC.oleiferabreeding, the thin coat, high seed yield and high oil content can be taken as the key research directions for future breeding, to increase the yield ofC.oleifera.

For ordinaryC.oleiferafruit produced in different regions, there is significant difference in the oil content related traits, mainly manifested in the oil content of fresh fruit, the oil content of fresh seeds, the oil content of dry seeds, and the oil content of seed kernel. Such situation is resulted from many factors. (i) Differences inC.oleiferavarieties[7]. In this experiment, the ordinaryC.oleiferain 18 counties (cities) belongs to different varieties, their biological characteristics are different, which will influence their oil content. (ii) Differences in breeding management measures and cultivation area. In this experiment, some of the selected ordinaryC.oleiferasamples are planted in large field, some are planted on hills with relatively high elevation, and some are planted on slopes[3]. These regions adopt different breeding management methods, some regions adopt extensive management method, and the soil, water, and fertilizer management methods are inadequate. ForC.oleifera, fruit grows generally in July and oil grows generally in August[10]. If in this period, no effective measure is taken, theC.oleiferayield and oil content will be inevitably affected[8]. In summary, the oil content ofC.oleiferais closely connected with the variety, but also with the picking time, planting region, cultivation technology, and management measures[11]. Therefore, in the process ofC.oleiferaindustry, it is recommended to select excellent varieties, adopt proper picking time, and take adequate cultivation and management measures.