Effect of Paclobutrazol and Analogs on Growth, Yield, Fruit Quality, and Storage Potential of ‘Delicious’ Apples

Abstract

A postbloom foliar application of 1500 and 3000 ppm paclobutrazol (PB) increased flesh firmness of ‘Delicious’ apple ( Malus domestica Borkh.) but reduced seed number and fruit size at harvest. The following year, flowering was not affected, but fruit set was increased. A decrease in terminal growth, leaf size, fruit L/D ratio, fruit size, pedicel length, and fruit soluble solids were also observed with the high rate of PB. PB increased fruit flesh calcium and total yield, and retarded fruit ripening. Dichlorobutrazol (DCB) did not affect final terminal growth but reduced L/D ratio, pedicel length, and fruit size the year after application. Following storage, flesh firmness of PBtreated fruit was not influenced, but senescent breakdown was dramatically reduced. Retarded ripening and reduced senescent breakdown were attributed to increased calcium in fruit flesh. Variability in terminal growth was increased as the inhibitory effects of PB dissipated. Three years after application, fruit L/D ratio and pedicel length were decreased, even though there was no longer a reduction in terminal growth. Chemical names used: ( 2RS, 3RS )-1-(2,2-dichlorophenyl-4-4-dimethyl-2-(1 H ,1,2,4-triazol-lyl)pentan-3-ol (paclobutrazol); (2 RS , 3 RS )-1-2,2-dichlorophenyl-4,4-dimethyl-2-(1 H 1,2,4-triazol-lyl)pentan-3-ol (dichlorobutrazol).