Aroma is an important quality trait of grapes and often the focus of consumers, viticulturists and grapevine breeders. Kyoho is a hybrid between Vitis vinifera and Vitis labrusca with a strawberry-like scent, while 87-1 is an early-ripening mutant of Muscat hamburg, belonging to Vitis vinifera, with a rose scent. In this study, we compared their aroma compositions and concentrations during berry development by headspace-SPME combined with gas chromatography-mass spectrometry (GC-MS), and analyzed the expression differences of enzyme-encoding genes in the LOX-HPL, MEP and MVA metabolic pathways by qRT-PCR. Twelve esters were detected in Kyoho during the whole berry development and they were abundant after veraison, but no esters were detected in 87-1 berries. Linalool was the dominant terpene among the 14 terpenes detected in 87-1 berries, while limited amounts of terpenes were detected in Kyoho berries. qRT-PCR analysis indicated that the low expression of VvAAT might explain the low content of ester volatiles in 87-1 berries, and the low expression of coding genes in the MEP pathway, especially VvPNLinNer1, might be the reason for the low content of volatile terpenes in Kyoho berries. The results from this work will promote our understanding of aroma metabolic mechanisms of grapes, and offer some suggestions for grape aromatic quality improvement.

Composting is an environment-friendly and sustainable way to transform grape branches (GBs) into a useful product. Different parameters can differently affect fertilizer quality. Here, the compost product nutrient content was evaluated using an L9 orthogonal array (parameters, nitrogen source: chicken manure, sheep manure, urea; stirring temperature: 50, 60, 70 °C; initial pH: 6, 7, 8; conditioning agent: calcium superphosphate, zeolite, and copper sulfate). Among the treatments, the T3 (chicken manure, 70 °C, pH = 8, copper sulfate), T2 (chicken manure, 60 °C, pH = 7, zeolite), and T9 (urea, 70 °C, pH = 7, calcium superphosphate) had high gray relational grades (0.7424, 0.7132, 0.7110, respectively). The nitrogen source type (R = 0.1140) had the greatest influence on the nutrient content of the final product, followed by the stirring temperature (R = 0.1104), the conditioning agent (R = 0.0522), and the initial pH (R = 0.0408). Finally, the best nitrogen source of the grape branch compost was chicken manure, the best stirring temperature was 70 °C, the best initial pH was 7, and the best conditioning agent was zeolite. An experimental verification showed that the weighted correlation degree of the optimal treatment predicted by the orthogonal experiment increased by 3.63%.