Effects Of Pre-harvest Ethephon Treatment On Cracking And Contents Of ’Huashuo’ Camellia Oleifera Fruit

Camellia oleifera Abel.is an important woody edible oil tree species in China.The camellia oleifera variety ’Huashuo’ has a thick fruit peel,which makes it difficult to remove the peel after harvest and does not crack during the fruit ripening period.In this study,the camellia oleifera cultivar ’Huashuo’ was used as the test material,and different concentrations of ethephon were treated 15 days before harvest.The direct measurement method,Soxhlet extraction method,and gas chromatography were used to determine and analyze the effects of ethephon(ETH)treatment on the cracking effect,fruit character indicators,oil yield,and fatty acid composition of camellia oleifera fruits,and transcriptome analysis was conducted on the treated materials,Screening out differentially expressed genes that promote fruit cracking and alter fatty acid composition under the influence of ethylene,with the aim of providing a theoretical basis for the application of plant growth regulators in production to simplify the peeling of camellia oleifera fruits.The main research findings are as follows:1.Changes in ACC content in the peel of Camellia oleifera during fruit development and differences between cracked and normal fruits.The variation pattern of endogenous amino cyclopropane-1-carboxylic acid(ACC)content in the peel of ’Huashuo’ camellia oleifera during fruit development is that as the fruit develops,the endogenous ACC content in the peel gradually increases.At the period when the fruit development speed reaches its fastest,the endogenous ethylene content in the peel reaches its maximum,and then begins to decrease.And in August to September,when the ’Huashuo’ Camellia oleifera fruit is most prone to natural cracking,the endogenous ethylene content in the kernels of the cracked fruit increased by 18.73%compared to the normal fruit,but there was no significant difference in the oil content between the two.In terms of fatty acid composition,the relative content of oleic acid,linolenic acid,and arachidonic acid in the cracked fruit was significantly lower than that in the normal fruit(P<0.01),and the relative content of linoleic acid and palmitic acid was significantly higher than that in the normal fruit(P<0.05).2.The effect of different concentrations of ethephon treatment before harvest on the fruit and leaves of camellia oleifera.After pre harvest treatment with different concentrations of ethephon,the fruit cracking rate of camellia oleifera increased with the increase of treatment concentration;In terms of fruit trait indicators of camellia oleifera,different concentrations of ethephon treatment before harvest had no significant impact on fresh fruit weight,transverse and longitudinal diameter,peel thickness,and fresh seed percentage.However,in terms of kernel moisture content,ethephon treatment can significantly reduce the kernel moisture content,and the higher the treatment concentration,the more obvious it is;Pre harvest treatment with different concentrations of ethephon significantly increased the sugar content in camellia oleifera seeds(P<0.01).In addition,pre harvest treatment with different concentrations of ethephon had no significant effect on the pigment content of camellia oleifera leaves.3.The effect of pre harvest treatment with different concentrations of ethephon on the oil content and fatty acid composition of camellia oleifera seeds.In two consecutive years of experiments,pre harvest treatment with different concentrations of ethephon had no significant effect on the oil content of seed kernels,but had a significant impact on the fatty acid composition of camellia oil.In terms of unsaturated fat,the relative content of oleic acid(85.92%)in the 1.5 g/L ethephon treatment group was significantly lower than that in the control group(86.78%),while the relative content of linoleic acid(4.33%)and linolenic acid(0.25%)were increased by 17.98%and 19.05%respectively compared with the control group;In terms of saturated fatly acids,both 0.5 and 1.0 g/L concentrations of ethylene can significantly reduce the relative content of palmitic acid and stearic acid,while 1.5 g/L ethylene treatment can significantly increase the relative content of palmitic acid and stearic acid.4.The transcriptome analysis of camellia oleifera peel was carried out.Through transcriptome analysis on the peel of ’Huashuo’ camellia oleifera treated with clean water and 1.5 g/L exogenous ethephon,40.16 Gb Clean Data was obtained,and the Q30 base percentage was 93.33%or more.Functional annotation was performed on Unigene,including comparisons with NR,Swiss Prot,KEGG,COG,KOG,GO,and Pfam databases.Among 2983 upregulated and 3560 downregulated differentially expressed genes,most of the differentially expressed genes were enriched in pathways such as linoleic acid and linolenic acid metabolism,plant hormone signal transduction,carbon metabolism,starch and sucrose metabolism.Among these genes,we identified 17,including ethylene synthesis and signal transduction(ACO,ERF)and cellulose degrading enzyme(EG,β-G)The differential genes related to fatty acid synthesis and metabolism(FAD,LOX),starch and sucrose metabolism(HK,DLAT),and transcription factors(MYB,bZIP,Dof),as well as their expression in the peel and kernel,indicate that the cellulose degrading enzyme gene(EG,β-G)Fatty acid synthesis and metabolism genes(LOX)are key genes that cause cracking and changes in fatty acid composition in camellia oleifera fruits.In summary,pre harvest treatment with 1.5 g/L ethephon on camellia oleifera’Huashuo’ can promote the cracking of mature camellia oleifera fruit and increase its relative content of linoleic acid and linolenic acid,providing theoretical basis and guidance for simplifying post harvest treatment using plant growth regulators in production.