Formation of flavonoids and chlorogenic acid in apples as affected by cropload

The effects of crop load on the concentrations of flavonoid and chlorogenic acid in skin and on quality characteristics of mature fruit has been studi ed. 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, respective ly, were established on 'Jonagold' apple trees by fruit thinning 8 weeks af ter fall bloom (FB). Also three crop load levels of about 60, 100 and 140 f ruits per tree (about 35, 50 and 70 t/ha), representing low, moderate and h igh loads, respectively, were established by thinning 'Red Elstar' apple tr ees 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 fir mness were significantly higher than at high and moderate loads. However, t he concentrations of flavonoid and chlorogenic acid were not affected by cr op load. For 'Red Elstar', the time of thinning did not affect the concentr ations of flavonoid and chlorogenic acid in fruit skin or fruit weight, sol uble solids, acidity and firmness. Removal of only the interior fruits (abo ut one-third of total fruit) at about 4 weeks before expected commercial ha rvest did not influence the concentrations of flavonoid and chlorogenic aci d or quality of the remaining exterior fruits of either 'Jonagold' or 'Elst ar'. The results indicate that assimilate availability is not a major regul atory factor in flavonoids and chlorogenic acid formation in apples. (C) 20 01 Elsevier Science B.V. All rights reserved.