Exogenous application of prohexadione-calcium promotes fruit colour development of 'Cripps Pink' apple

Abstract

The effects of various concentrations and number of sprays of prohexadione-calcium(ProCa) and summer pruning (SP) alone on fruit colour and other quality parameters of ‘Cripps Pink’ apple were investigated. The treatments were: (i) no spray as control, (ii) SP, (iii) 250 mg L-1 with two sprays (3 and 33 days after full bloom (DAFB), (iv) 500 mg L-1 with two sprays (3 and 33 DAFB), (v) 750 mg L-1 with two sprays (3 and 33 DAFB), (vi) 250 mg L-1 with three sprays (3, 33 and 63 DAFB),(vii) 500 mg L-1 with three sprays (3, 33 and 63 DAFB), and (viii) 750 mg L-1 with three sprays (3, 33 and 63 DAFB). Spraying was done on fruits of a whole treated tree. The reduction in shoot length was pronounced after the second spray application of ProCa regardless of concentration. The treatment of two sprays of500 mg L-1 ProCa and three sprays 500 and 750 mg L-1 of ProCa showed the highest reduction in the shoot length as compared to control. The SP alone, and three sprays of 500 and 750 mg L-1 ProCa at 3, 33 and 63 DAFB, respectively significantly improved percent red blush, percent fruit for export, higher a* value and lower b*,L* and hue angle values on the fruit as compared to control. The treatment of three sprays of 750 mg L-1 ProCa resulted the highest accumulation of cyanidin 3-ogalactosidein apple skin.However, the three sprays of 500 mg L-1 treatment exhibited the comparable concentration of cyanidin 3-O-galactoside with the treatment of three sprays of 750 mg L-1 ProCa. Fruit quality parameters such as fruit firmness, soluble solids concentration (SSC) and titratable acidity (TA) resulted in inconclusive outcomes, but still meet the export requirements. In conclusions, three spray applications of ProCa (500 mg L-1) on 3, 33 and 63 DAFB reduced shoot growth, improved fruit colour, accumulation of cyanidin 3-O-galactoside and also maintained other fruit quality attributes in ‘Cripps Pink’ apple.