Effects of BTH application at veraison on berry coloration and quality of ‘Red Globe’ berries

Abstract:【Objective】The growing season of table grapes in southern China happens in rainy season withserious rain-transmitted diseases, which cause serious losses. Rain-shelter cultivation is an effectivemethod to prevent rain-transmitted diseases in the production of table grapes and has been widely appliedin 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 cul⁃tivated under rain-shelter in southern China but often has the problem of poor coloration due to weak lightand high temperature. Plant elicitors are regarded as effective tools in inducing the biosynthesis of second⁃ary metabolites such as flavonoids in plants. In this work, BTH (benzo (1,2,3) thiadiazole-7- carbothioicacid S-methyl ester, Bion®), one of the synthetic elicitors, was sprayed on‘Red globe’grape clusters, andthe color parameters (L*, a*, b*), the anthocyanin content, the expression of genes involved in anthocyaninbiosynthesis 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 rainsheltercultivation in Xundian county, Kunming City from July 10th to August 9th of 2014. Four treatmentswere studied (the control and three BTH doses) in a complete randomized block design. There were threeblocks with a total of 12 plots, each of which had five grapevines. Ten grape clusters were kept in eachgrapevine 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 earlystage of veraison. 4 and 7 days later, the grape clusters were sprayed again avoiding spraying the chemicalonto the leaves. On the 10th day after the first treatment, ten grape berries were randomly sampled from theupper, middle and lower parts of grape clusters in each of the 12 plots, and berry sampling was carried outevery five days till harvest (30th day). And berry length, diameter, shape index (length/diameter), weightand CIE parameters were measured. Color indexes for red grapes (CIRG) included the values of L*, a* andb*. Soluble solids (SSC), titratable acid (TA) and total soluble sugar contents were analyzed after grapeflesh was homogenated. Grape skins were peeled from berries and grinded in liquid nitrogen and anthocy⁃anin content was determined with photospectrometry method. Individual anthocyanins were detected withhigh-performance liquid chromatography (HPLC) method.【Results】The CIRG and total anthocyanincontent of‘Red Globe’berries treated with BTH in the early stage of veraison were all significantly in⁃creased compared to control berries. The results showed that 60 mg·L^-1 BTH treatment had the highestvalues of both CIRG and total anthocyanin content, followed by 120 mg·L^-1, and then 30 mg·L^-1. Mean⁃while, 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 whileF3’5’H gene at harvest was significantly down-regulated by preharvest treatment of 60 mg·L^-1 BTH. Thedown-regulation of F3’5’H gene might block the flux to the delphinidin branch pathway, while the cyani⁃din synthesis pathway was enhanced because of the significant up-regulation of F3’H gene. The individu⁃al anthocyanins in‘Red Globe’grape skins detected by HPLC mainly were derivatives from the cyanidinpathway such as peonidin-3-O-glucoside (Pn) and cyanidin-3-O-glucoside (Cy); derivatives from thedelphinidin branch such as malvidin-3-O-glucoside (Mv), petunidin-3-O-glucoside (Pt) and delphini⁃din-3-O-glucoside (Dp) accounted for only a very small percentage of the total anthocyanins. Thus, wesuggested that BTH might stimulate anthocyanin biosynthesis mainly through F3’H branch. BTH treatments significantly increased soluble solid content and decreased titratable acid content, which resultedin significant increase in SSC/TA. BTH treatments did not affect berry diameter, length, shape index andweight 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 re⁃sistance (SAR), is effective in enhancing red color by up-regulating genes and transcription factors in⁃volved in anthocyanin biosynthesis, accelerating ripeness and improving quality of‘Red Globe’berries un⁃der rain-shelter cultivation. Among all the treatments, 60 mg·L^-1 BTH treatment was the most effective one.