Anthocyanins in red grape skin have a positive effect on fruit color and human health. The effect of foliar potassium application on anthocyanin accumulation in grape skin is not well understood. The study aimed to better understand the mechanism of anthocyanin accumulation in grape skin in response to foliar sprays of K₂SO₄ and KH₂PO₄. In this study, we investigated the effects of foliar application of KH₂PO₄ (T2), K₂SO₄ (T1) and distilled water (CK) on the skin color of ‘Kyoho’ grapes at mid-ripe and mature stages. At 90 and 110 days after full bloom (DAFB), T2 had the greatest total soluble solids (TSS), flavonoid and total anthocyanin contents, followed by T1 and CK. At two stages, the titratable acid content decreased and the juice pH increased under T2 treatment relative to CK. T1 and T2 had lower lightness (L*) than CK, and the color index of red grapes (CIRG) under T1 and T2 increased at two stages compared to CK. KEGG metabolic pathway analysis revealed that flavonoid biosynthesis was the most significantly enriched pathway in CK vs. T2 at 90 and 110 DAFB. At 90 DAFB, T2 had higher expressions of phenylalanine ammonia-lyas (PAL), cytochrome P450 CYP73A100 (CYP73A), 4-coumarate: CoA ligase (4CL), chalcone synthase (CHS), flavanone 3-dioxygenase-like (F3H) and UDP glucose: flavonoid 3-o-glucosyl transferase (UFGT) than CK and T1. Foliar application of potassium fertilizer may accelerate anthocyanin accumulation by altering the transcript levels of PAL, CYP73A, 4CL, CHS, F3H, and UFGT of the flavonoid biosynthesis.

Conventional irrigation methods decrease greenhouse soil aeration, which leads to restricted root growth and reduced soil fungal abundance in greenhouse grapes. In this study, aerated irrigation equipment was used to investigate the effects of aerated irrigation on the biomass accumulation, root growth, and soil fungal community structure of grape seedlings. The results show that aerated irrigation significantly increased the root length, root surface area, root volume, and number of root tips by 38.5%, 32.1%, 62.1%, and 23.4%, respectively, at a soil depth of 20–40 cm (p ≤ 0.05). The chao1 index and ACE index of fungi at different soil depths under aerated irrigation were higher than those without aerated treatment; aerated irrigation changed the relative abundance of dominant fungi in rhizosphere soil. At a soil depth of 20–40 cm, aerated irrigation increased the abundance of Fusarium by 42.2%. Aerated irrigation also contributed to the abundance of the beneficial fungal genera Mortierella, Cladosporium, and Glomus. At a soil depth of 0–20 cm, the abundance of Mortierella in the soil that received aerated treatment was 180.6% higher than in the control treatment. These findings suggest that aerated irrigation is a promising strategy for the promotion of grape root growth and biomass accumulation, and it can also increase the abundance of some beneficial fungi.

As a widely distributed fruit, grapes are susceptible to oxidative damage during storage and transportation, resulting in declining quality and commodity value. This study aimed to investigate the effects of preharvest application of different concentrations of multi-walled carbon nanotubes (MWCNTs) on the postharvest quality of ‘Flame Seedless’ grapes. The results showed that low-concentration (25 and 50 mg L⁻¹) MWCNTs treatments maintained the comprehensive quality index, firmness, soluble sugar, titratable acid, pH value, and ascorbic acid (AsA) content of grapes. MWCNTs at 25 and 50 mg L⁻¹ increased the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and ascorbic acid (APX). Furthermore, MWCNTs reduced the malondialdehyde (MDA) content and decreased the accumulation of excessive reactive oxygen species (ROS) in grape peel and pulp tissues. In addition, transmission electron microscopy (TEM) images demonstrated that MWCNTs were absorbed by parenchymal cells in the grape peel and pulp through the epidermal cell layer. MWCNTs with a specific concentration can be used as a new inducer for the biosynthesis of antioxidants to reduce oxidative damage in grapes during storage.

Anthocyanins, soluble sugars, and organic acids play a vital role in the color and flavor of grape berries. N and KH₂PO₄ are essential nutrients for grape growth and development. However, the research on the effects of foliar spraying of KH₂PO₄ on the skin color and flavor of grapes under different N levels were not systematic. In this study, “Flame seedless” grapes were used as the test material. There were six treatments in this experiment, including low nitrogen (LN), low nitrogen + KH₂PO₄ (LNK), moderate nitrogen (MN), moderate nitrogen + KH₂PO₄ (MNK), high nitrogen (HN), and high nitrogen + KH₂PO₄ (HNK). Foliar spraying of KH₂PO₄ on grapes significantly increased total K, anthocyanin contents, and the color index of red grapes (CIRG) in LN, MN, and HN. In the N and KH₂PO₄ treatments, foliar spraying of KH₂PO₄ significantly increased the content of methylated, acetylated, and coumarylated anthocyanins under MN treatment. The glucose and fructose contents of MNK were the highest compared to other treatments. The sole use of N showed the highest glucose and fructose contents with MN application. Anthocyanin had a significant positive correlation with soluble sugars; and showed a significant negative correlation with organic acids. Overall, foliar spraying of 0.5% KH₂PO₄ improved the color and flavor of “Flame seedless” grapes under all N levels, with the most significant effect at MN.

It is very important to promote plant growth and decrease the nitrogen leaching in soil, to improve nitrogen (N) utilization efficiency. In this experiment, we designed a new fertilization strategy, fruit tree hole storage brick (FTHSB) application under subsurface drip irrigation, to characterise the effects of FTHSB addition on N absorption and utilization in grapes. Three treatments were set in this study, including subsurface drip irrigation (CK) control, fruit tree hole storage brick A (T1) treatment, and fruit tree hole storage brick B (T2) treatment. Results showed that the pore number and size of FTHSB A were significantly higher than FTHSB B. Compared with CK, T1 and T2 treatments significantly increased the biomass of different organs of grape, N utilization and ¹⁵N content in the roots, stems and leaves, along with more prominent promotion at T1 treatment. When the soil depth was 15–30 cm, the FTHSB application significantly increased the soil ¹⁵N content. But when the soil depth was 30–45 cm, it reduced the soil ¹⁵N content greatly. T1 and T2 treatments obviously increased the activities of nitrite reductase (NR) and glutamine synthetase (GS) in grape leaves, also the urease activity(UR) in 30 cm of soil. Our findings suggest that FTHSB promoted plant N utilization by reducing N loss in soil and increasing the enzyme activity related to nitrogen metabolism. In addition, this study showed that FTHSB A application was more effective than FTHSB B in improving nitrogen utilization in grapes.

Ethylene is commonly used in agricultural production for fruit ripening and degreening. However, further exploration is needed on how to apply it in its gaseous form in practical production. This study compared the effects of ethylene gas (E1: 100 ppm, E2: 120 ppm, E3: 150 ppm) application via subsurface drip irrigation (SDI) and fruit surface spraying of ethephon solution (ETH) on the quality and coloration of ‘Flame Seedless’ grape fruit during veraison. The effects of applying ethylene gas via SDI were most pronounced at 3, 6, and 9 days post-treatment. At day 6 post-treatment, E2 had a higher soluble solid content (SSC), solid–acid ratio, and anthocyanin content than ETH, although by day 15 most differences among the ethylene gas treatments, ETH, and CK had diminished. E2 also increased the abundance of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO) and ACC synthase (ACS) and the expression of VvCHI, VvCHS, VvGST, and VvF3H at day 3 post-treatment, and all of these were also higher than in the ETH treatment. The gaseous nature of ethylene allows it to contact the fruit effectively and to be taken up by the plant through multiple pathways, so that the grapes respond faster to ethylene gas than to ETH treatment.