Effect of a postbloom naphthaleneacetic acid thinning spray and hand thinning on quality and quantity of pear fruit (Pyrus communis L.) cv. Harrow Sweet

The effect of naphthaleneacetic acid (NAA) and hand thinning on quality and quantity of pear fruit (Pyrus communis L.) cv. Harrow Sweet was investigated in 2005, 2006 and 2007. The experiment included the following treatments: an unsprayed control, hand thinning to 3 fruit cm-2 of trunk cross-sectional area (TCSA), hand thinning to 6 fruit cm-2 of TCSA, NAA at 8 mg L-1 (2005-2007), NAA at 16 mg L-1 (2006-2007) and NAA at 20 mg L-1 (2007). The same treatments were applied to the same trees in each of the three years. NAA thinning did not reduce yield per tree and had no negative effect on fruit set, yield efficiency, or crop load in any of the years. In 2005 and 2006, NAA and hand thinning significantly increased fruit diameter and weight. In 2007, only NAA at 20 mg L-1 significantly increased fruit diameter and weight relative to the control. Fruit firmness was not influenced by NAA or hand thinning in 2005 or 2007, but in 2006, hand-thinned fruits were significantly less firm than control fruit. Hand thinning to 6 fruit cm-2 of TCSA increased fruit soluble solids content in 2006 and 2007. Neither NAA nor hand thinning influenced total sugars or organic acids in fruit. Key words: Yield, sugars, organic acids, HPLC