Carlos Acosta, Guadalupe Partida, Kaylah Vasquez, Eve Laroche-Pinel, and Luca Brillante*
*Department of Viticulture and Enology, California State University Fresno, 2360 E Barstow Ave, Fresno, CA, 93740 (lucabrillante@csufresno.edu)

The table grape market is ever-changing due to pandemic developments, issues with transportation, and emerging competitive markets. As growers are expected to produce grapes of extraordinary standards to obtain decent prices and export quality, many have turned to plant growth regulators (PGRs). PGRs are hormonal biostimulant chemicals that, when used correctly, can improve fruit size, color development, root growth, and cell division. Applied incorrectly, they can have devastating effects on fruit quality, yield, and flavor profile. We examined the independent effect and interaction of two PGRs: abscissic acid (ABA) and ethephon, (2-chloroethyl) phosphonic acid, crossed with water stress or its lack at veraison. The PGRs were applied using the maximum allowed rate at the onset of veraison, in conjunction with the water deficit treatment, which consisted of three weeks without irrigation until plants reached a midday stem water potential of -1.5 MPa, followed by rewatering until the stem water potential was equivalent to the non-stressed control. The trial was a complete randomized block design, with eight treatments including control and four replicates per treatment. The research was conducted in a commercial table grape vineyard planted with Sheegene 12 x Freedom located in Madera, California. The vineyard was five years old, cane pruned, and trellised on a gable system with a 4 × 2 m spacing between rows and plants, respectively. Ethephon produced the greatest amount of packed fruit at the end of the experiment. Water deficit treatments, followed by ethephon treatments, ranked higher on the spectrum for culls. Berry firmness and weight were better in the non-water deficit treatments. No clear disparities in berry length or width were noted. First-pass fruit was larger than the second-picked fruit and was consistently heavier.

Funding Support: None to disclose