Effects of BTH application at veraison on berry coloration and quality of ‘Red Globe'berries
[Objective]The growing season of table grapes in southern China happens in rainy season with serious rain-transmitted diseases,which cause serious losses.Rain-shelter cultivation is an effective method to prevent rain-transmitted diseases in the production of table grapes and has been widely applied in southern China,although rain shelter reduces light penetration and leads to significant delay in the accumulation of sugar and pigments.‘ Red Globe'(Vitis vinifera L.) is one of the important table grapes cultivated under rain-shelter in southern China but often has the problem of poor coloration due to weak light and high temperature.Plant elicitors are regarded as effective tools in inducing the biosynthesis of secondary metabolites such as flavonoids in plants.In this work,BTH (benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester,Bion(R)),one of the synthetic elicitors,was sprayed on ‘Red globe'grape clusters,and the color parameters (L*,a*,b*),the anthocyanin content,the expression of genes involved in anthocyanin biosynthesis as well as qualities in ‘ Red globe'grape were analyzed to evaluate the effects of BTH on table grapes.[Methods] The experiment was carried out in a 4-year-old ‘ Red Globe'vineyard under rainshelter cultivation in Xundian county,Kunming City from July 10th to August 9th of 2014.Four treatments were studied (the control and three BTH doses) in a complete randomized block design.There were three blocks with a total of 12 plots,each of which had five grapevines.Ten grape clusters were kept in each grapevine with 70-80 berries in every cluster.Grape clusters were evenly sprayed with water or three concentrations of BTH solutions (30 mg· L-1,60 mg· L-1 and 120 mg· L-1) at 10:00 in the morning at the early stage of veraison.4 and 7 days later,the grape clusters were sprayed again avoiding spraying the chemical onto the leaves.On the 10th day after the first treatment,ten grape berries were randomly sampled from the upper,middle and lower parts of grape clusters in each of the 12 plots,and berry sampling was carried out every five days till harvest (30th day).And berry length,diameter,shape index (length/diameter),weight and CIE parameters were measured.Color indexes for red grapes (CIRG) included the values of L*,a* and b*.Soluble solids (SSC),titratable acid (TA) and total soluble sugar contents were analyzed after grape flesh was homogenated.Grape skins were peeled from berries and grinded in liquid nitrogen and anthocyanin content was determined with photospectrometry method.Individual anthocyanins were detected with high-performance liquid chromatography (HPLC) method.[Results] The CIRG and total anthocyanin content of ‘Red Globe'berries treated with BTH in the early stage of veraison were all significantly increased compared to control berries.The results showed that 60 mg· L-1 BTH treatment had the highest values of both CIRG and total anthocyanin content,followed by 120 mg· L-1,and then 30 mg· L-1.Meanwhile,the expression of genes involved in anthocyanins biosynthesis such as PAL,CHS1,CHS2,CHI1,CHI2,F3'H,F3H1,F3H2,DFR,LDOX,UFGT-2 and VvmybyA1 were significantly up-regulated while F3'5'H gene at harvest was significantly down-regulated by preharvest treatment of 60 mg· L-1 BTH.The down-regulation of F3'5'H gene might block the flux to the delphinidin branch pathway,while the cyanidin synthesis pathway was enhanced because of the significant up-regulation of F3'H gene.The individual anthocyanins in ‘Red Globe'grape skins detected by HPLC mainly were derivatives from the eyanidin pathway such as peonidin-3-O-glucoside (Pn) and cyanidin-3-O-glucoside (Cy);derivatives from the delphinidin branch such as malvidin-3-O-glucoside (My),petunidin-3-O-glucoside (Pt) and delphinidin-3-O-glucoside (Dp) accounted for only a very small percentage of the total anthocyanins.Thus,we suggested that BTH might stimulate anthocyanin biosynthesis mainly through F3'H branch.BTH treatments significantly increased soluble solid content and decreased titratable acid content,which resulted in significant increase in SSC/TA.BTH treatments did not affect berry diameter,length,shape index and weight except that 120 mg· L-1 BTH treatment significantly decreased berry diameter at the 30th day.[Conclusion]These results suggested that BTH,as an effective elicitor in activating plant systemic acquired resistance (SAR),is effective in enhancing red color by up-regulating genes and transcription factors involved in anthocyanin biosynthesis,accelerating ripeness and improving quality of ‘Red Globe'berries under rain-shelter cultivation.Among all the treatments,60 mg·L-1 BTH treatment was the most effective one.
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