Foliar Application of Abscisic Acid to Day-Neutral Strawberry Cultivars to Influence Fruit Production
Deyton, D. E., C. E. Sams, and J. C. Cummins.  2017.  Plant Growth Regulator Society of America, Anchorage, Alaska, August 6-10, 2017.

Research was conducted on strawberry plants grown in pots in a greenhouse to determine if repeated sprays of abscisic acid (ABA) effected vegetative growth and fruit quality. ‘Seascape’ and ‘San Andreas’ day-neutral frigo strawberry plants were planted on 9 June 2016 in 3.8 L pots containing 1:1 mixture of perlite and peat moss. The plants were grown in a greenhouse with fertigation supplying 80 mg/L of nitrogen (in a modified half strength Hoagland solution) after the third week of establishment. The plants were sprayed with 0, 5, 10, 15, 25, 50 or 100 mg∙L-1 of ABA biweekly from 25 August 2016 through 22 March 2017. Treatments were randomized in a split plot design with four replications of two cultivars, seven ABA treatments and four plants per replication. Plants within each treatment were removed from the trial and sprayed with a small hand-held sprayer. The media surface was shielded from ABA contact to reduce root uptake. Plants were harvested approximately twice per week from 30 September 2016 until 31 March 2017. Fruit were graded into commercial (>10 g) and non-commercial (<10 g and deformed fruit) and weighed and counted at each harvest. ABA sprays of 25 to 100 mg∙L-1 reduced the total number and weight of ‘Seascape’ and ‘San Andreas’ fruit harvested during the harvest period (P ≤ 0.05). Commercial fruit yield (g/plant) of ‘San Andreas’ plants treated with 50 or 100 mg∙L-1 was reduced 18% and 50%, respectively, compared to untreated plants. Commercial yield of ‘Seascape’ plants treated with 50 or 100 mg∙L-1 was reduced by 40% and 70%, respectively. ABA did not affect fruit soluble solid content and had little effect on berry size. Slight phytotoxicity of older leaves was noted on plants treated with >10 mg∙L-1 ABA. Blossoms were counted after three different spray dates in March and rated for phytotoxicity. Treatments did not affect apparent blossom mortality, but plants sprayed with 25, 50, or 100 mg∙L-1 ABA had 21%, 23%, and 48% fewer total number of blossoms than untreated plants.