Objective:
The‘Christmas Rose’grape is a type of the late-maturing cultivars which is widely planted in China. It is favored by consumers because of its delicate flesh，resistance to storage and transportation，and high quality. However，in some areas，the coloration of the‘Christmas Rose’grape was not 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 coloration of fruit by promoting the accumulation of anthocyanin. This study is to explain the effect of different concentrations of exogenous prohydrojasmon(PDJ)，methyl jasmonate(MeJA) on the coloration and quality of the‘Christmas Rose’grape so as to provide some theoretical evidence to improve coloration and 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 treatments were applied in three replications and arranged in a complete randomized block design，with a single grapevine for each replication. Two different concentrations (10 mg·L– 1，50 mg·L– 1) of prohydrojasmon，methyl jasmonate were respectively applied to the‘Christmas Rose’grape berries. The aqueous solutions of both treatments and control involved 0.1% Tween-80 and 1% ethanol. The experimental grape berries were sprayed uniformly with aqueous solution twice at the beginning of veraison and 7 days later after the first application. After the first treatment，samples were taken every 10 days until the fruit was ripe when the seeds were completely brown and the soluble solids content no longer increased. A total of 40 single berries from the top，middle and bottom parts of randomly selected 10 grape bunches were picked and brought to the laboratory for analysis. The coloration of the grape berry was measured by a Minolta colorimeter and expressed as the L value (the fruit surface light brightness)，a value (color component of red and green)，b value (color component of yellow and blue) and CIRG value (color index of red grape). Anthocyanin content in the skin extraction was measured by the pH differential method. The contents of chlorophyll a and chlorophyll b in the skin extraction were tested according to the Arnon’s method. The soluble solids content of the fruit was measured by a PR-101 refractometer. The titratable acid in the grape juice was titrated by 0.1 mol·L– 1 NaOH 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 method. The pedicel endurable pulling force and berry endurable pressing force were measured by a Digital Push & Pull Tester. In addition，the berry weight，berry length，berry diameter，and the content of vitamin C were also determined. All analyses were performed using Excel and SPSS software.
Results:
During the ripening period of the grapes that were treated or not treated，the L value，and b value decreased，while the a value，and CIRG value increased，the brightness of the grape skin declined and the coloration of the grape skin was transformed from green to red. The grape berries treated with PDJ，and MeJA 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-1 PDJ. At harvest，the CIRG value of 50 mg·L-1 PDJ-，MeJA- treated grapes reached 4.61 and 4.50 respectively 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 declined gradually in the grape skin. The content of anthocyanin in the grape skin treated with PDJ，and MeJA was obviously higher than the control. The 50 mg·L-1 PDJ，and MeJA treated grapes presented a higher an⁃ thocyanin content than the 10 mg·L-1 PDJ，and MeJA- treated grapes. The PDJ treatment had a better effect than the MeJA treatment under the same concentration on increasing the content of anthocyanin. At harvest，the anthocyanin content in the grape skin treated with 50 mg·L-1 PDJ，and 50 mg·L-1 MeJA was respectively 31.2%，and 20.0% higher than the control. The content of chlorophyll a and chlorophyll b in the grape skins treated with PDJ，and MeJA were lower compared with the control. The PDJ，and MeJA treatments promoted the synthesis of anthocyanin while enhanced the degradation of chlorophyll a and chlorophyll b，and the coloration of the grape berry improved. The 50 mg·L– 1 PDJ treatment performed best in improving the coloration of the grape berries among all of the treatments. During the period of maturation，the soluble solids content of grapes treated with PDJ，and MeJA were obviously higher compared with the grapes that were untreated. The 50 mg·L-1 PDJ，and MeJA treatments were more effective in increasing the content of soluble solids than the 10 mg·L-1 PDJ，and MeJA treatments. There were no obvious differences between the treated and untreated grapes on the titratable acid content. The application of PDJ，and MeJA promoted the accumulation of total phenolics，and flavonoids in the skin at harvest，and total phenolics in the skin treated with 50 mg·L-1 PDJ，and MeJA were respectively 36.4%，and 29.0% higher than the control. The application of PDJ，and MeJA significantly enhanced the content of vitamin C in the fruit，however，the berry weight，berry length and berry diameter were not influenced. The grape treated with PDJ，and MeJA had a higher nutritional quality，in addition，the PDJ，and MeJA treatment did not have a negative effect on fruit yield. The pedicel endurable pulling force and berry endurable pressing force were not influenced by the PDJ，and MeJA treatment. The phenomenon of berry drop did not happen in the treated grapes. There was no difference between the treated and untreated grapes on resistance 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. Under the same concentration，the PDJ treatment had a better effect than the MeJA treatment on improving coloration and the quality of grapes; the 50 mg·L-1 PDJ，and MeJA treatment showed a better effect than the 10 mg·L-1 PDJ，and MeJA treatment. Among all of the treatments，the 50 mg·L-1 PDJ treatment was the most effective in improving the coloration and quality of grapes in the trial.
By SUN Xiaowen，GAO Dengtao，WEI Zhifeng，GUO Jingnan*，CAO Meng
（Zhengzhou Fruit Research Institute，CAAS，Zhengzhou 450009，Henan，China）
lin-chemical.com 