Effect of Fruiting and Biennial Bearing Potential on Spur Quality and Leaf Gas Exchange in Apple

Abstract

Uniform annual apple (Malus ·domestica) fruit production is highly dependent on consistent flower formation from year to year, as inconsistent flowering can lead to the biennial bearing observed in some high-value cultivars. The presence of fruit on a spur has been considered the main cause of the expression of biennial bearing and the inhibition of flower initiation, with a number of theories being introduced to explain the phenomenon. In the current experiment, individual spurs of annual bearing cultivars (Gala, Ruby Jon, and Pink Lady) and biennial bearing cultivars (Honeycrisp, Fuji, and Golden Delicious) were thinned to a single fruit or completely defruited at petal fall. Spurs were sampled at the end of the growing season. Effects of fruiting on spur characteristics such as spur and bourse leaf area, stomatal density, leaf gas exchange, and flower formation were determined. Across all cultivars, the presence of fruit on a spur did not affect spur characteristics or flower formation compared with nonfruiting spurs. Similarly, flowering was unaffected by those factors associated with greater spur carbohydrate status, such as bourse leaf area and assimilation rate. Cultivars with greater transpiration and stomatal conductance (g s ) rates had lower rates of flower formation. Future studies should focus on xylem flow and expression of genes regulating flowering and plant growth regulators in annual and biennial bearing cultivars.

Weather Influences on the Gas Exchanges of Neem Trees

“…Plants engaged in higher food production with increased leaf area during the pre-flowering phase, whereas higher metabolic activity of plants during the reproduction phase increased the water and energy requirements, which could explain why photosynthetic rate was higher during the pre-flowering phase than the flowering phase. This was in line with results of [8][9][10][11]. Alternate flowering trees exhibited a higher photosynthetic rate than other trees, which was consistent with the findings of [12] in the Apple tree.…”

Air-Pruning Containers Modify Root and Scion Growth and Alter Resource Allocation of Bench-Grafted Apple Plants

“…Scion vigor may also be associated with concentrations or ratios of growth inhibiting to promoting compounds [31] or nutrient acquisition and transport properties of a given rootstock-scion combination [32,33]. Of the three cultivars evaluated, gas exchange of 'Honeycrisp' was similar to Fuji and higher than Gala [34], yet field-grown 'Honeycrisp' trees completed their terminal extension growth by mid-season; terminals of container-produced trees only elongated an additional ~20% after 15-August, which was markedly less than 'Fuji' or 'Gala'. The early seasonal cessation of 'Honeycrisp' terminal growth is a common observation in the orchard and is hastened by the presence of fruit.…”

“…The ability of 'Gala' to produce similar canopy growth with significantly less root was not observed for the other cultivars and is illustrated by a smaller difference in the percentage of total plant DMC in roots versus shoots when comparing the two production systems (Figure 2). An alternative index is the ratio of total canopy leaf area (cm 2 ) to total root length (cm) (34). More specifically, the total absorptive root length, since presumably plant investment in leaf area is dependent on the capacity of the ephemeral, absorptive roots to meet its evaporative demand.…”

Molecular Basis of Flower Formation in Apple Caused by Defoliation and Gibberellins

“…Not only are they the main receptor for environmental signals but they also produce carbohydrates and plant growth regulators. Recently, we showed that flowering did not appear to be related to factors associated with spur carbohydrate status, suggesting a direct role of genes regulating flowering and plant growth regulators (Elsysy et al, 2019). Flower induction genes have been shown to be active in the leaves (Hanke et al, 2007).…”