Resarech on grading evaluation about fruit quality of ‘Summer Black' grape

Abstract:【Objective】The planting area of‘Summer Black'grape have increased year by year. However,owing to the high yield cultivation, improper use of plant growth regulator and management differences,the quality standard of fruits varies with fruit characters such as bunch size, fruit size, fruit color, flavor quality, and so on, leading to poor fruit quality and the sales difficulty and restriction of further development. In addition, there is no national standard and agriculture industry standar about fruit quality grades of‘Summer Black'grape in China. Therefore, it is high time for us to carry out the research on grade evaluation of the fruit quality, exploring the discrepancy of fruit quality and formulating fruit quality grade standard of‘Summer Black'grape.【Methods】The fruits of‘Summer Black'grape produced in Henan were used as experimental materials. The grape bunches were divided into nine different levels according to the bunch weights, which were ≤400 g, 400-500 g, 500-600 g, 600-700 g, 700-800 g, 800-900 g,900-1 000 g, 1 000-1 100 g and ≥1 100 g. The berries were divided into eight different levels according to the single berry weight, which were ≤4 g, 4-5 g, 5-6 g, 6-7 g, 7-8 g, 8-9 g, 9-10 g and ≥10 g. Several fruit characters were measured, including bunch weight, berry weight, soluble solid content, total acid, tannin content, color index. The fruit quality was comprehensively evaluated and classified by principal component analysis and cluster analysis.【Results】Fruit characters at different bunch weight levels were different. When the bunch weights of‘Summer Black'ranged from 286.4 g to 1 260.6 g, the coefficient variation was 32.49%. While the berry weights ranged from 5.68 g to 11.1 g, the coefficient variation was19.8%. The coefficient variations of ratioes of SSC to acid and tannin content were all higher than 16%.The coefficient variation of total acid content, soluble solid content and color index were all higher than10%. The soluble solid content, ratio of SSC to acid and color index were significantly and negatively correlated with bunch weight, and the total acid was positively correlated with bunch weight. The result of principal component synthetic evaluation showed that when the bunch weights were smaller than 400 g the evaluating value of fruits was the highest, and while the bunch weigh was larger than 900 g the evaluating value was the lowest. The fruit quality decreased with increment of bunch weight. The fruit quality for different bunches and berry weights levels were classified into four types and three types respectively by cluster analysis. The classification results showed that the fruit quality was the highest when the bunch weights was 400-500 g, the medium when the bunch weights was 500-900 g and the lowest when the bunch weights were larger than 900 g. The fruit quality was the highest when the simgle berry weights were 6-7 g the medium when the simgle berry weight were 7-9 g and 5-6 g, the lowest when the simgle berry weight was smaller than 5 g and larger than 9 g. Based on the results of principal component analysis and cluster analysis considering and commercial operability, the standard of bunch weight for the first class of fruit quality of‘Summer Black'grape were 400 g to 800 g, and the single berry weight were 5 g to9 g. The bunch weight for the second class and the third class were smaller than 400 g and larger than 800 g respectively, and the single berry weight were smaller than 5.0 g and larger than 9.0 g respectively.【Conclusion】The quality of‘Summer Black'grape was negatively correlated with bunch weight. It is important to control the bunch weight lower than 800 g and the single berry weight smaller than 9.0 g. The fruit quality grade standard of‘Summer Black'grape in Henan province was formulated initially. The ideal character values of high-quality grape were that the bunch weight ranged from 400 g to 800 g, single berry weight ranged from 5 g to 9 g, soluble solid content was over 18%, total acid content was lower than0.5%, tannin content was lower than 1.1×10~3mg·kg^-1, and the bunch color was violet black.