Abscission Mechanism Studies With Apple Fruitlets1

A computer model of a growing apple (Malus domestica Borkh.) shoot was used to estimate the effects of light and temperature on the C balance of a shoot. Long-term average solar radiation (langley/day) and maximum and minimum temperatures from Geneva, N.Y., were used as weather inputs. To simulate other weather conditions, solar radiation was increased or decreased by 150 langley/day, and maximum and minimum temperatures increased or decreased by 5.6°C. Both a short shoot of 2 cm and a long shoot of 50 cm final length were simulated. The model output indicated that increased light reduced carbohydrate import and caused earlier and greater export. Increased temperature increased carbohydrate import and the subsequent rate of carbohydrate export. The short shoot had a greater initial rate of C export and continued to export more total carbohydrates than the long shoot for about 30 to 50 days after budbreak. Slow leaf area development at a given temperature had little effect on carbohydrate import but delayed the beginning of export.

Section: Resultsmentioning

confidence: 88%

“…It has been hypothesized that reduction of metabolite translocation from foliage to fruit is the primary mechanism that stimulates abscission of pre-June drop apples (12,13). Therefore, the early C balance of a growing shoot could affect fruit set and eventual yield.…”

mentioning

confidence: 99%

Carbon Balance Model of a Growing Apple Shoot: II. Simulated Effects of Light and Temperature on Long and Short Shoots

Johnson

Lakso

1986

“…Studies over many years have suggested that the presence and activity of early leaf area is important to fruit set and yield (1,3,9,16,17,19,23). Defoliation of spur leaves prior to fruit set caused severe reductions in fruit set while defoliation of shoot leaves had relatively little effect (6,16), emphasizing the importance of the spur leaves.…”

mentioning

confidence: 99%

Leaf Area Development Patterns in Young Pruned and Unpruned Apple Trees

Lakso

1984

Six-year-old ‘Empire’/Malling 7 (M7) apple (Malus domestica Borkh.) trees were left unpruned or pruned moderately during dormancy, and early-season leaf area development patterns were examined. Pruning markedly shifted leaf area distribution from spur to extension shoot. Leaf area at and shortly after bloom nearly doubled in the unpruned trees due to the increased percentage of the leaf area in rapidly developing spurs; however, the final total leaf areas were not affected significantly by the pruning. Leaf area development in all trees slowed dramatically around full bloom. Yields were reduced in the pruned trees primarily due to fewer flower clusters. Leaf areas per tree correlated well with percentage of sky values from fisheye photography.

“…The availability and distribution of light within the apple tree canopy is known to influence tree growth and fruit produc tion (9). Shading reduced fruit set (1,14,20) and fruit quality (12,18,19,20) but mixed effects have been reported for vege tative growth (1,2,13,16) and tissue carbohydrate content (1,7,10). Gardner et al (6) concluded that higher light and temperature during and shortly after bloom in 'Delicious' increased set but Dennis (5) re-evaluated their data and found little statistical basis for their conclusion.…”

mentioning

confidence: 99%

Influence of Altered Light Levels on Growth and Fruiting of Mature ‘Delicious’ Apple Trees1

Doud

Ferree

1980

Available light in mature apple trees (Malus domestica Borkh.) of an unknown red strain of ‘Delicious’ on Mailing (M) 9 rootstocks was altered throughout the 1978 growing season by the use of reflectors, overhead lights, and shade material. Undertree reflectors increased light within the tree canopy about 20% at anthesis, 10-30% through mid-season, and 35% at harvest. Light was reduced within the canopy 20% at bloom and 10-20% the remainder of the season by over-tree shade. Shading reduced fruit set by 62% and reflectors had no effect. Red fruit color was reduced by shading and increased by reflector treatments, particularly in the lower half of the tree. Total yield and soluble solids were decreased by shading, but no significant differences were obtained by attempts to increase light. Reflectors and overhead light increased and shading reduced specific leaf weight. Shading increased levels of P, K, B and Zn and reduced Ca and Mg. None of the treatments altered total nonstructural carbohydrate (CHO) levels in several tissues at bloom. However, shading reduced percent CHO in both spur and shoot leaves in June and July, but increased CHO in these tissues at harvest.