Abstract
ABSTRACT This study aimed to evaluate the effects of different crop load levels on apple trees’ yield and physiological characteristics, emphasizing the relationship between stem water potential and crop load and the link between trunk diameter growth and crop load. It was conducted in 2014 at Station Expérimentale Fruits et Légumes (SUDEXPE-CEHM) in Southern France. The ‘JoyaTM’ apple on Pajam-1 rootstock was used as the plant material. Trees were subjected to hand thinning to obtain four final crop load levels as high (100%; 10 fruit/cm2 of branch cross-sectional area (BCSA)), medium-high (75%; 7.5 fruit/cm2 of BCSA), medium-low (50%; 5 fruit/cm2 of BCSA) and low (25%; 2.5 fruit/cm2 of BCSA). The four crop load levels were set up in a randomized block design with four replications, and each plot was formed of five uniform trees. Stem water potential was weakly affected by crop load but was mainly driven by vapor pressure deficit. The maximum daily trunk diameter, by and large, reduced while crop load level increased. The increase in crop load level was negatively related to fruit size, acidity and soluble solids content. Crop load did not affect bitter pit incidence. However, in parallel to the increasing crop load level, cumulative yield, yield efficiency and water productivity increased.
Highlights
The primary goal in fruit growing is to access as maximum yield as possible of better-quality crops at minimum cost (Westwood, 1995)
The relationships between Stem Water Potential (SWP) and Vapor pressure deficit (VPD) were significant in all crop load levels (Figure 4)
The higher absolute SWP values are expected at high crop load levels because of the higher transpiration and the high resistance to water flow from soil to the stem (Bustan et al, 2016; Naor et al, 2008)
Summary
The primary goal in fruit growing is to access as maximum yield as possible of better-quality crops at minimum cost (Westwood, 1995). Crop load management is a pivotal practice to reach this target. It influences many physiological processes in fruit orchards such as source-sink carbon relationships, water status and water consumption (Bustan et al, 2016). The fruit are strong carbohydrate sink, and high crop load levels can stunt the vegetative growth (Yuri et al, 2011) and return bloom of trees (Elsysy and Hirst, 2017). Apple growers set crop load, as a vigor control tool, to bend the main leader and lateral branches down, especially in the training systems for high-density apple orchards such as Centrifugal Training, to achieve the balance between vegetative growth and fruiting (Atay, 2016). High crop load levels deplete nutrients in plants and especially carbohydrates required for vegetative growth (Goldschmidt, 1999)
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