Ethylene Gas Applied Through Subsurface Drip Irrigation Accelerates Early Berry Coloration and Anthocyanin Accumulation in ‘Flame Seedless’ Grapes Compared with Ethephon

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.