The synthetic cytokinin CPPU increases fruit size and yield of 'Spadona' and 'Costia' pear (Pyrus communis L.)

The effects of the synthetic cytokinin CPPU, derived from phenylurea, on fruit size and yield of the small-fruited, low-chilling requiring 'Spadona' and 'Costia' pears, were examined in Israel. CPPU caused appreciable increases in fruit size of both cultivars, when applied at 10-20 ppm, two weeks after full bloom, whereas application after four weeks gave only small effects or none. The effect of CPPU on fruit growth was already evident two months after application, when the fruits reached 35-40 mm in diameter. The large increase in fruit size occurred without thinning and, therefore it must be attributed directly to the effect of CPPU. CPPU increased fruit size with no influence on fruit shape, seed number and it did not reduce return bloom in the following spring. A semi-commercial application of 10 ppm CPPU increased fruit size by 40% in 'Spadona' and 80% in 'Costia' with an increase of about 50% in the total yield of each cultivar. Our findings demonstrate the effectiveness of CPPU in these pear cultivars and show that it has a significant potential to improve cropping, without any negative aspects.