Paclobutrazol, Gibberellin, and Cytokinin Effects on Growth, Development, and Histology of Apple Pedicels and Fruits

Abstract

Abstract The effects of the plant growth regulators (PGR) gibberellins A 4+7 (GA 4+7 ; 25, 50, and 150 mg·liter −1 ), BA (25 mg·liter −1 ), and GA 4+7 + BA (Promalin; 25 mg·liter −1 ) on pedicel growth and fruit development of ‘McIntosh’ and ‘Spartan’ apple ( Malus domestica Borkh.) trees previously treated with foliar- or soil-applied paclobutrazol (PBZ) were examined. By full bloom, pedicels had completed the elongation growth phase regardless of treatment. Pedicel length was very sensitive to PBZ treatment since it was reduced logarithmically in response to dose. No differences in pedicel diameters were found. PBZ decreased fruit fresh weight, dry weight, and fruit length and diameter in both ‘McIntosh’ and ‘Spartan’ trees. The adverse effects of PBZ carryover on fruit-quality factors such as size and pedicel length were not overcome with GA 4+7 (25 or 50 mg·liter −1 ), BA, or Promalin (25 mg·liter −1 ) applied when the king-bloom was in full bloom. Reversal of PBZ-induced pedicel length inhibition was only observed with GA 4+7 (150 mg·liter −1 ) applied prior to the main period of pedicel elongation. BA alone had no effect on any fruit growth parameters. PBZ reduced pedicel and fruit cell length, while GA 4+7 (150 mg·liter −1 ) applied at 2 weeks before full bloom increased pedicel cell length. Chemical names used: β-[(4-chIorophenyl)methyl]-α-(1,1-dimethylethyl)-1 H -1,2,4-triazol-1-ethanol (paclobutrazol); N -(phenylmethyl)-1 H -purine-6-amine (BA); (1α,2β4aα,4bβ,10β)-2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-l,10-dicarboxylic acid l,4a-lactone (GA 4+7 ).