Formation of flavonoids and chlorogenic acid in apples as affected by crop load

The effects of crop load on the concentrations of flavonoid and chlorogenic acid in skin and on quality characteristics of mature fruit has been studied. Three crop load levels of about 50, 100 and 200 fruits per tree (about 35, 60 and 100 t/ha), representing low, moderate and high loads, respectively, were established on 'Jonagold' apple trees by fruit thinning 8 weeks after fall bloom (FB). Also three crop load levels of about 60, 100 and 140 fruits per tree (about 35, 50 and 70 t/ha), representing low, moderate and high loads, respectively, were established by thinning 'Red Elstar' apple trees at FB, and 4 and 8 weeks after FB. Similar results were found for both cultivars. At a low crop load, fruit weight soluble solids, acidity and firmness were significantly higher than at high and moderate loads. However, the concentrations of flavonoid and chlorogenic acid were not affected by crop load. For 'Red Elstar', the time of thinning did not affect the concentrations of flavonoid and chlorogenic acid in fruit skin or fruit weight, soluble solids, acidity and firmness. Removal of only the interior fruits (about one-third of total fruit) at about 4 weeks before expected commercial harvest did not influence the concentrations of flavonoid and chlorogenic acid or quality of the remaining exterior fruits of either 'Jonagold' or 'Elstar'. The results indicate that assimilate availability is not a major regulatory factor in flavonoids and chlorogenic acid formation in apples. (C) 2001 Elsevier Science B.V. All rights reserved.