ASHS 2015 Annual Conference

'Autumn Royal', a black seedless late-season table grape variety has a high retail demand with naturally large berries, good flavor, and attractive color. One limiting factor for 'Autumn Royal' grape production is proper color development due to its propensity to overcrop. Plant growth regulators are widely used to increase berry size and enhance color development. Research emphasis has recently focused on the concept of water productivity, which is the amount of marketable product produced per unit of water consumed in evapotranspiration (ET_c). Table grape growers tend to over-irrigate to ensure optimum quality grapes. Plant growth regulator treatments included gibberelic acid (GA₃) and Ethrel^® applications and a combination of both with an untreated control. Three irrigation treatments were applied: grower control at 120% ETc; early regulated deficit irrigation (RDI) initiated at fruit set irrigated at 80% ET_c until veraison; and late RDI initiated at veraison irrigated at 80% of ET_c until harvest. Initial results showed that the combination of irrigation regimes with PGR treatments had no significant effect on berry size (g) or cluster weight (g), but the cumulative 19 lb boxes packed was higher for the early RDI treatment. Total skin anthocyanin content (mg/kg) was significantly higher for the Ethrel^® and combined PGR treatments during early RDI. The late RDI treatment showed higher skin anthocyanins for only the combined PGR treatment. Berry firmness was higher for the combined PGR and early RDI treatments. After cold storage trials berry firmness was significantly higher for GA₃ and the combined PGR treatments. The late RDI treatment had the firmest berries of the three irrigation regimes. Preliminary results showed that the RDI early treatment was the better performer, even in drought situations, but must be combined with PGR’s. PGR applications are needed in 'Autumn Royal' production and they have an additive effect on yield and berry color. Using PGRs can enhance berry firmness and storage ability. Also, the combined effects of early RDI and PGR applications would increase yield and storage ability and enhance color development. Irrigation savings of 2 acre-inches was achieved with RDI treatments and resulted in full berry color development. This is an ongoing project that presented initial results based on the 2014 growing season.