BENZYLADENINE AFFECTS CELL-DIVISION AND CELL-SIZE DURING APPLE FRUIT THINNING

Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneace tic acid (NAA) were applied postbloom as fruitlet thinning agents to m ature 'Empire' apple (Malus domestica Borkh.) trees. BA, NAA, and CB r educed fruit set and yield per tree, and increased fruit size, percent dry weight, soluble solids content and return bloom. Fruit size was r educed, return bloom, length : diameter ratio and flesh firmness were increased, and fruit set and yield unaltered by DM. Although fruit set and yield were similar for BA, NAA, and CB, BA treated fruit were lar ger, indicating that BA increased fruit size beyond the effect attribu table to chemical thinning alone, BA increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division, NAA, CB and DM had no effect on cell division rate, Mea n cortical cell diameter at harvest was increased by NAA and CB and re duced by DM. Cell diameter at harvest in BA-treated fruit was similar to the control, These data support the hypothesis that BA-induced frui t size increase in 'Empire' apple results from greater numbers of cell s in the fruit cortex, whereas the fruit size increase due to NAA or C B is a consequence of larger cell size. Chemical names used: N-(phenyl methyl)-1H-purine-6 amine [benzyladenine (BA)]; 1-napthaleneacetic aci d (NAA); 1-naphthalenyl methylcarbamate [carbaryl(CB)]; butanedioic ac id mono (2,2-dimethyl hydrazide) [daminozide (DM)].