| Grapes(e.g.Vitis vinifera L.)are one of the most important,economic and largest fruit crops grown worldwide.China rank second in terms of total grape growing area and first in table grape production with 34%of total table grape production worldwide.Ideally,grape is a summer crop,harvested once in a year in temperate regions.However,“two-crop-a-year”or“double cropping viticulture system”has been developed and being popularly practiced by the growers of sub-tropical southern China in recent decade where grapevine are subjected to pruning and application of chemical treatments which enables growers to harvest grape in both summer and winter season without overlapping.To know further details about the unique viticulture system,research programs were carried out to study the effects of seasonal variation on yield and bioactive compounds,as influenced by vineyard soil variability and cultural practices in‘Summer Black’(Vitis vinifera L.×V.labruscana L.)table grape.In addition,comparative transcriptome analysis was performed to know about the accumulation and biosynthesis of anthocyanin related gene expression at molecular level.1.Environmental factors greatly influence grape quality.Among them,the effect of vineyard soil variability on yield and quality of table grape is less studied.In this study,the effects of soil moisture at different elevations(192 m,202 m and 212 m,respectively)on chlorophyll fluorescence,yield and quality traits of grapes grown in vineyards were compared.The soil moisture content of vineyard at different altitudes was significantly different,the highest moisture was recorded in the lower site of the vineyard and the lowest moisture was in the upper site.The fluorescence intensity of O,J,I and P phases of chlorophyll fluorescence kinetics curve of grape leaves in upper and middle sites were significantly higher than that in lower site of the vineyard due to the change of soil moisture.Fluorescence intensity was higher in winter season compared to summer season.The effects of soil moisture on the initial fluorescence(F_o),the potential activity of PSII(F_v/F_m),the maximum fluorescence(F_m),the variable fluorescence(F_v)of chlorophyll a fluorescence of grape leaves in the two seasons were significantly different.F_o in the upper site was the highest and the lowest in the lower site,while F_m,F_v and F_v/F_m in the upper leaves were significantly lower than those in the upper sites.F_v/F_m in the summer leaves were significantly higher than those in the winter leaves.In both winter and summer,the number of cluster per vine,cluster weight,single fruit weight and yield per plant in the middle site were significantly higher than those in the upper and lower sites,and the content of soluble solids(TSS),phenolic compounds and antioxidant activities in the lower site was significantly lower than that in the middle and upper sites.The effective water content of soil(0-20 cm and 20-40 cm)in summer and winter vineyards were 37%and 50%,27%and 35%respectively,which were found to be beneficial for the production of grape in a double cropping system viticulture.2.In another study,variation in phenolic compounds and antioxidant activities of‘Summer Black’grape was examined under cultural practices such as cluster thinning and berry thinning;also,any influence of seasonal variation in berry attributes was studied in a double cropping system.The results indicated that both cluster thinning and berry thinning and their combination significantly influenced yield reduction,improved phenolic compounds and antioxidant activities and grape berries were found to be more uniform in size compared to control,as a result of modifying the source-sink ratio.Among the cultural practices,combined application of cluster and berry thinning resulted in berries with increased TSS,total phenolic and flavonoid compounds,anthocyanin content and antioxidant activities followed by cluster thinning and berry thinning.Significant difference was also found in grapes from summer and winter season regarding quality parameters.Although yield was higher in summer season,grape berries from winter season was found better in all other quality attributes compared to summer.3.Experiment was also carried out to study the impact of cultural practices,such as berry thinning and basal leaf removal on yield,chemical composition and the biosynthesis of anthocyanin related gene expressions from the onset of veraison to harvest(E-L 35 to E-L 38)in both summer and winter cropping season.Results revealed that the combined application of leaf removal and berry thinning significantly increased the total soluble solid and anthocyanin content in grape berry skin followed by leaf removal and berry thinning compared to control.Gene expression pattern revealed that expression of most of the anthocyanin biosynthesis-related genes were significantly up-regulated in combination of berry thinning and leaf removal.Gene expressions were also higher in winter compared to summer from veraison to harvest.4.Finally,transcriptome analysis was performed with three developmental stages(E-L33,36 and 38)of berries from summer and winter season to compare the transcriptional regulation of anthocyanin biosynthesis in grape skin.The result revealed that 581 and1668 genes in summer and 1001 and 2577 gene in winter were up-regulated in pre-veraison(E-L 33)to full-ripening stage(E-L 38)respectively.After the analysis of functional category enrichment and differential gene expression(DEGs)patterns,16genes were selected as candidate gene.Among the genes PAL2,GST2,CHS2,CHS3,CHI,F3′H,DFR,LAR,FLS and 3GT genes were found to be significantly expressed in full-veraison stage compared to other stages in both summer and winter season.Whereas,PAL2,CHI,CHS2,F3′H,3GT and DFR were up-regulated in summer and F3′5′H,CHS1,CHS3,FLS,LAR and GST2 were up-regulated in winter season respectively.The expression of selected DEGs were further confirmed by quantitative real-time PCR(qRT-PCR).Expression patterns from qRT-PCR were in agreement with the RNA-Seq data except three genes named F3′H,3GT and 5GT.Compared to summer,anthocyanin related genes were significantly more expressed in winter in all the three developmental stages.The seasonal variation in temperature,sunlight and rainfall is primarily attributed to that difference.In conclusion,results from the above studies indicate that vineyard soil variability with soil moisture and different viticulture practices such as cluster thinning,berry thinning,and leaf removal significantly influence the yield and quality of‘Summer Black’table grape.Combined application of cluster thinning and berry thinning as well as berry thinning and leaf removal in combination was found better than others including control.Moreover,grape harvested from winter season was found to be better in all quality aspects of biochemical compositions and transcriptional regulations.Thus,the studies will enrich the theoretical research on two-crop-a-year viticulture system and highlights the potential benefits of growing table grape for high total yield with good quality berries for sub-tropical regions. |
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