Differences in the Aroma Profiles of Seedless-treated and Nontreated 'Shine Muscat' Grape Berries Decrease with Ripening
In the production of seedless table grapes, it is conventional to use plant growth regulators including gibberellins. Little is known about the differences in aroma volatiles between seedless-treated grapes and nontreated (seeded) grapes. Therefore, in this study, the aroma volatile profiles of seedless-treated and nontreated 'Shine Muscat' grape berries during ripening were compared using gas chromatography-mass spectrometry. Measurements of volatiles during ripening showed 202 peaks in the seedless-treated and nontreated whole grape berries. According to two-way analysis of variance, the number of volatiles with differences between seedless-treated and nontreated berries and/or between ripening stages was 123, whereas those with no differences between treatments and between ripening stages was 79. Two-way hierarchical clustering analysis for the 123 volatiles showed that seedless-treated berries at the early ripening stages were separated from the other berries, and the seedless-treated and nontreated berries at the post-ripening stage were classified into the same cluster. At the early ripening stage, more lipoxygenase-pathway volatiles were produced in the seedless-treated berries than in the non-treated ones. Linalool compounds increased in both seedless-treated and nontreated berries with ripening. Gene expression profile comparisons using principal component analysis of RNA-sequencing data showed that the seedless-treated berries ripened earlier than the nontreated berries at the early ripening stage. The number of differentially expressed genes in the seedless-treated berries decreased during ripening. Using weighted gene co-expression network analyses, 12 modules and 24 modules were detected in berry skin and flesh, respectively. The correlation analysis revealed that 33 volatiles correlated with four modules in the skin and 50 volatiles correlated with nine modules in the flesh. Most of the volatiles correlated with these modules were those that showed significant differences between treatments and/or ripening stages by two-way analysis of variance. The differences in the aroma volatile profiles between seedless-treated and nontreated berries decreased as harvest was delayed, suggesting that delaying the harvest may make it possible to bring the aroma of seedless-treated 'Shine Muscat' berries closer to the original aroma of the seeded berries. Overall design: Volatiles profiles in the seedless- and non-treated 'Shine Muscat' grape berries were compared using GC/MS. RNA-sequencing and weighted gene co-expression network analyses were conducted to identify the specific modules correlated with the volatile profiles.