|Keywords: ||Apogee, ethephon, gibberellin biosynthesis inhibitor, Malus domestica, prohexadione-calcium, water stress|
Slowing early-season shoot growth in fruit trees with plant growth regulators can promote flower initiation and return cropping.
Transient water stress may also have this effect or perhaps enhance these growth regulator effects.
Post-harvest urea may result in more N available for flower bud development and thus result in stronger flowers and improved cropping.
In this factorial experiment, we imposed water stress to one-half of the seven-year-old 'Golden Delicious'/M.9 apple trees in each block, by stopping irrigation for a period of 3 weeks between 35 and 56 days after full bloom (AFB). Within each whole unit (no water stress or water-stressed), the following chemical treatments were randomly allocated at 2 x 2 x 2 factorial: a) 0 or 250 ppm prohexadione-Ca (ApogeeTM) applied 28 days AFB; b) 0 or 300 ppm ethephon applied twice, 35 and 71 days AFB; and c) 0 or 4% urea foliar sprayed twice at 7-day intervals, starting 10 days after harvest.
Shoot growth was most markedly reduced by Apogee, while water stress and ethephon treatments were less effective.
Apogee did not affect fruit size and yield but slightly decreased fruit firmness and acidity.
Ethephon substantially reduced fruit size and yield but increased firmness, soluble solids, and acidity.
Water stress substantially reduced fruit size and yield but had no effect on these fruit quality attributes.
With respect to fruit nutrients, Apogee increased N, K and Mg concentrations; ethephon increased N, P, K, Mg and B; and water stress increased only K and B. Fruit Ca was unaffected by any treatment.
Mean dry weight of dormant spur flower buds was reduced by all treatments except ethephon.
Total [N] of the buds was increased by all treatments, with the urea effect being the most marked; dormant twig [N] was increased only by urea.
Return flowering was improved only by ethephon.
Fall urea sprays increased fruit set in the subsequent season.
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