Effect of jasmonates on coloration and quality of the 'Christmas Rose' grape berry

Abstract: 【Objective】The‘Christmas Rose'grape is a type of the late-maturing cultivars which is widelyplanted in China. It is favored by consumers because of its delicate flesh,resistance to storage and trans-portation,and high quality. However,in some areas,the coloration of the‘Christmas Rose'grape wasnot very good because of high temperature and humidity,which affected its internal and external qualities. In recent years,researchers found that jasmonates,which widely exist in plants,could improve col-oration of fruit by promoting the accumulation of anthocyanin. This study is to explain the effect of differ-ent concentrations of exogenous prohydrojasmon(PDJ),methyl jasmonate(MeJA) on the coloration andquality of the‘Christmas Rose'grape so as to provide some theoretical evidence to improve colorationand quality of this grape berry.【Methods】The trial was conducted at the experimental farm of the Zheng-zhou Fruit Research Institute,CAAS,on uniform 6-year-old‘Christmas Rose'grapevines. All treat-ments were applied in three replications and arranged in a complete randomized block design,with a sin-gle grapevine for each replication. Two different concentrations(10 mg·L-1,50 mg·L-1) of prohydrojas-mon,methyl jasmonate were respectively applied to the‘Christmas Rose'grape berries. The aqueous so-lutions of both treatments and control involved 0.1% Tween-80 and 1% ethanol. The experimental grapeberries were sprayed uniformly with aqueous solution twice at the beginning of veraison and 7 days laterafter the first application. After the first treatment,samples were taken every 10 days until the fruit wasripe when the seeds were completely brown and the soluble solids content no longer increased. A total of40 single berries from the top,middle and bottom parts of randomly selected 10 grape bunches werepicked and brought to the laboratory for analysis. The coloration of the grape berry was measured by a Mi-nolta colorimeter and expressed as the L*value(the fruit surface light brightness),a*value(color compo-nent of red and green),b*value(color component of yellow and blue) and CIRG value(color index of redgrape). Anthocyanin content in the skin extraction was measured by the p H differential method. The con-tents of chlorophyll a and chlorophyll b in the skin extraction were tested according to the Arnon's meth-od. The soluble solids content of the fruit was measured by a PR^-101 refractometer. The titratable acid inthe grape juice was titrated by 0.1 mol·L^-1 Na OH according to the Gao's method. The total phenolics,and flavonoids in the skin extraction were determined respectively according to the Jia and Meyer's meth-od. The pedicel endurable pulling force and berry endurable pressing force were measured by a DigitalPush & Pull Tester. In addition,the berry weight,berry length,berry diameter,and the content of vita-min C were also determined. All analyses were performed using Excel and SPSS software.【Results】Dur-ing the ripening period of the grapes that were treated or not treated,the L*value,and b*value de-creased,while the a*value,and CIRG value increased,the brightness of the grape skin declined and thecoloration of the grape skin was transformed from green to red. The grape berries treated with PDJ,andMeJA had a higher a*value,CIRG value and a lower L*value,b*value than the control. The highest a*value,CIRG value and the lowest L*value,b*value were found in the grapes treated with 50 mg·L^-1PDJ.At harvest,the CIRG value of 50 mg·L^-1PDJ-,MeJA-treated grapes reached 4.61 and 4.50 respective-ly while the CIRG value of the untreated grapes was only 4.04. During the ripening period of the grapes,the anthocyanin content rose gradually,in contrast to chlorophyll a and chlorophyll b which declinedgradually in the grape skin. The content of anthocyanin in the grape skin treated with PDJ,and MeJA wasobviously higher than the control. The 50 mg·L^-1PDJ-,and MeJA-treated grapes presented a higher an-thocyanin content than the 10 mg·L^-1PDJ-,and MeJA-treated grapes. The PDJ treatment had a bettereffect than the MeJA treatment under the same concentration on increasing the content of anthocyanin. Atharvest,the anthocyanin content in the grape skin treated with 50 mg·L^-1PDJ,and 50 mg·L^-1MeJA wasrespectively 31.2%,and 20.0% higher than the control. The content of chlorophyll a and chlorophyll b inthe grape skins treated with PDJ,and MeJA were lower compared with the control. The PDJ,and MeJAtreatments promoted the synthesis of anthocyanin while enhanced the degradation of chlorophyll a andchlorophyll b,and the coloration of the grape berry improved. The 50 mg·L-1PDJ treatment performedbest in improving the coloration of the grape berries among all of the treatments. During the period of mat-uration,the soluble solids content of grapes treated with PDJ,and MeJA were obviously higher comparedwith the grapes that were untreated. The 50 mg·L^-1PDJ,and MeJA treatments were more effective in in-creasing the content of soluble solids than the 10 mg·L^-1PDJ,and MeJA treatments. There were no obvi-ous differences between the treated and untreated grapes on the titratable acid content. The application ofPDJ,and MeJA promoted the accumulation of total phenolics,and flavonoids in the skin at harvest,andtotal phenolics in the skin treated with 50 mg·L^-1PDJ,and MeJA were respectively 36.4%,and 29.0%higher than the control. The application of PDJ,and MeJA significantly enhanced the content of vitaminC in the fruit,however,the berry weight,berry length and berry diameter were not influenced. The grapetreated with PDJ,and MeJA had a higher nutritional quality,in addition,the PDJ,and MeJA treatmentdid not have a negative effect on fruit yield. The pedicel endurable pulling force and berry endurable,not happen in the treated grapes. There was no difference between the treated and untreated grapes on re-sistance to storage and transportation.【Conclusion】Two different concentrations of exogenous PDJ,and MeJA improved coloration and quality of the‘Christmas Rose'grape berry compared with the control. Un-der the same concentration,the PDJ treatment had a better effect than the MeJA treatment on improvingcoloration and the quality of grapes; the 50 mg·L^-1PDJ,and MeJA treatment showed a better effect thanthe 10 mg·L^-1PDJ,and MeJA treatment. Among all of the treatments,the 50 mg·L^-1PDJ treatment wasthe most effective in improving the coloration and quality of grapes in the trial. This study focused on theeffect of PDJ,and MeJA on the coloration and quality of the‘Christmas Rose'grape from the physiologi-cal aspect. However,the specific mechanism of how PDJ,and MeJA influenced coloration and the quali-ty of grapes is not clear,and further research is still needed.