Effects of Crop Load on Fruiting and Gas-exchange Characteristics of `Braeburn'/M.26 Apple Trees at Full Canopy

Abstract

<jats:p>Effect of crop load on tree growth, leaf characteristics, photosynthesis, and fruit quality of 5-year-old `Braeburn' apple [<jats:italic>Malus sylvestris</jats:italic> (L.) Mill. var. <jats:italic>domestica</jats:italic> (Borkh.) Mansf.] trees on Malling 26 (M.26) rootstock was examined during the 1994-95 growing season. Crop loads ranged from 0 to 57 kg/tree [0 to 1.6 kg fruit/cm<jats:sup>2</jats:sup> trunk cross sectional area (TCA) or 0 to 8.7 fruit/cm<jats:sup>2</jats:sup> TCA]. Fruit maturity as indicated by background color, starch/iodine score, and soluble solids was advanced significantly on low-cropping trees compared to high-cropping trees. Whole-canopy leaf area and percentage tree light interception increased linearly with a significant trend as crop load decreased. From midseason until fruit harvest, leaf photosynthesis decreased significantly on lighter cropping trees and similarly, a positive linear trend was found between whole-canopy gas exchange per unit area of leaf and crop load. Leaf starch concentration in midseason increased linearly as crop load decreased, providing some explanation for the increased down-regulation of photosynthesis on trees with lower crop loads. After fruit harvest, the previous crop loads had no effect on leaf photosynthesis and preharvest differences in whole-canopy gas exchange per unit area of leaf were less pronounced. At each measurement date, daily whole-canopy net carbon exchange and transpiration closely followed the diurnal pattern of incident photosynthetic photon flux. The photochemical yield and electron transport capacity depended on crop load. This was due mostly to reaction center closure before harvest and an increased nonphotochemical quenching after harvest.</jats:p>

Influence of pre‐harvest calcium, potassium and triazole application on the proteome of apple at harvest

“…Several studies also showed an effect on fruit set depending on the actual compound used . Similar results were described by Palmer et al who reported increased yield and advanced maturity for light cropping trees while Wünsche et al only reported earlier maturation due to low crop load. Elgar et al reported a higher BBD incidence for light cropping trees and for later harvested fruit, but could not correlate BBD to fruit maturity.…”

Effect of late Spring defruiting on net CO2exchange and leaf area development in apple tree canopies

“…The progressive decrease in daily NCER canopy values from May to September may have favoured the leaf photosynthetic efficiency of trees with larger carbon demands. Follow-up studies are necessary to determine whether a greater vegetative response (i.e., 50% more growth compared to F trees) would have resulted in the vegetative sinks demonstrating greater relevance than that observed in this study; or whether the mere presence of a few fruits, as reported in Wünsche et al (2000), would have completely altered the observed effects relating to inhibition of leaf photosynthesis.…”

“…But even then, the timing of photosynthetic down-regulation in defruited trees could still vary, and the final result would prove difficult to predict. For instance, in an earlier study by Wünsche et al (2000), leaf photosynthetic downregulation accelerated in completely defruited trees, but did the opposite in lightly cropped apple trees.…”

Patterns of size and fate relationships of contiguous organs in the apple (Malus domestica) crown

“…Flowering is lateral on long shoots (i.e. with long internodes; as a rule of thumb, 5 cm; Wünsche et al ., 2000) and terminal on long and short shoots. In any given position within the tree architecture, a branch is made up of a sequence of vegetative and/ or reproductive annual shoots.…”