Effect of Abscisic Acid On Thinning and Return Bloom of Bartlett Pears

Abscisic acid (ABA) was applied at a rate of 500 ppm to ‘Bartlett’ pears in 2007 at  bloom, petal fall or the 10 mm stage of fruit development.  When final fruit set was taken, ABA reduced set at all times of application.  However, the application made at petal fall nearly defruited the trees and also resulted in extensive leaf abscission.  ABA applied at petal fall increase fruit size. In 2008 ABA was applied to ‘Bartlett’ pears at rates between 50 and 500 ppm when fruit size averaged 10 mm.  There was a quadratic and highly significant reduction in final frit set.  Fruit weight, fruit diameter, flesh firmness and soluble solids were increase linearly by ABA treatments.  A factorial experiment was also  done on Bartlett pears where ABA at 250 ppm was applied alone and in combination with 150 ppm benzyladenine (BA) when fruit averaged 10 mm in diameter.  ABA caused significant thinning, BA had no influence on fruit set and there was no interaction between ABA and BA.  BA increased fruit weight, fruit diameter and soluble solids at harvest.  ABA caused some leaf drop and the application of BA with ABA was not useful in reversing this response.