Effect Of Different Potassium Fertilizer Applications On Fruit Quality Of ’Summer Black’ Grapes And Mining Of Key Genes

’Summer Black’ originated in Japan and was introduced to China in 1998.It is one of the major varieties in the grape-growing region of southern China and is popular among consumers for its early maturity,high quality,and no kernels.It is one of the major grape varieties in southern China and is well liked by consumers for its early ripening,high quality,and seedless characteristics,and the reasonable application of potassium fertilizer in the vineyard has a greater impact on fruit quality.In this experiment,three different levels of potassium fertilizer(potassium sulfate)were applied at 50 and 57 days after bloom to 8-year-old ’Summer Black’ grapes.The three different levels of potassium fertilization were used to study the dynamic changes of fruit quality and sugar-acid content during fruit development of ’Summer Black’ grapes,with no potassium fertilization at 0 g/plant(K0-CK)as control.The genes and pathways related to fruit sugar and anthocyanin synthesis and potassium transport were screened by transcriptomics.The main results of the study are as follows:(1)Potassium application not only increased the potassium content in ’Summer Black’ grapes,but also significantly improved the intrinsic quality and color of ’Summer Black’ grapes.Potassium application significantly increased the content of soluble solids,soluble sugars,fructose,glucose and anthocyanins,reduced the content of titratable acid,tartaric acid and malic acid,and increased the sugar-to-acid ratio of the fruit.Soluble sugar content increased by 37.39%,31.10% and 32.59% and anthocyanin content increased by 49.78%,24.10% and 13.06% in K150,K300 and K450 treatments,respectively,during fruit ripening.The overall sugar content in the fruit showed an increasing trend during fruit ripening,which was consistent with the change in total anthocyanin,with the best effect of K150 treatment,and the appropriate concentration of potassium fertilizer was not the higher the better.(2)The transcriptomes of ’Summer Black’ grapes at different potassium levels-50 days after bloom(50 DAB-color change),64 days after bloom(64 DAB-mid development)and 78 days after bloom(78 DAB-ripening)-were sequenced using high-throughput sequencing technology.KEGG results showed that the differentially expressed genes in fruits at different potassium levels were mainly enriched in "enzyme activity regulation","carbohydrate catabolic process","ion transmembrane transport",and "glycolysis".The results of GO and KEGG showed that the differentially expressed genes were mainly concentrated in "enzyme activity regulation","carbohydrate catabolic process","ion transport across membrane","glycolysis and gluconeogenesis" and "flavonoid biosynthesis",which are related to fruit quality formation.(3)Based on transcriptome sequencing,biological analysis(WGCNA)identified11 key genes involved in fruit quality regulation(anthocyanin synthesis,sugar metabolism,and potassium transport),including GST,AT,UFGT1,UFGT2,UFGT3,SPS,HT,PK,KUP1,KUP2,and KUP3.The expression levels of 11 differentially expressed genes were determined by RT-q PCR,and the results showed that potassium application promoted anthocyanin accumulation during fruit development,which was associated with up-regulation of GST,AT and UFGT expression.At 78 DAB,the expression levels of UFGT1 and UFGT2 were higher,while those of UFGT3 and AT were lower,indicating that UFGT1 and UFGT2 acted mainly at the ripening stage,while UFGT3 and AT acted at the early stage.However,GST was higher both before and after ripening,indicating that GST is indispensable at both early and ripening stages.Potassium application also promoted fruit sugar accumulation,with higher expression levels of SPS and HT and lower PK at 78 DAB,indicating that SPS and HT acted mainly at the ripening stage,while PK acted mainly at the early stage.In addition,it promoted the up-regulation of KUP expression,which is the main cause of K accumulation in the fruit.These results suggest that potassium application promotes the growth and development of grape fruit,increases the synergistic effect between genes related to nutrient and sugar metabolism,and facilitates their transport between source pools,thus improving fruit quality during ripening.In conclusion,the rational use of potassium fertilizer can contribute to the improvement of grape fruit quality,but it should be applied in a cost-efficient manner.The results of the above study not only clarify the theoretical mechanism of potassium application to improve fruit quality,but also provide some theoretical support for accurate potassium supply to grapes.