Optimizing Crop Load for New Apple Cultivar: “WA38”

Abstract

Crop load management is growing increasingly important as a factor related to biennial tendencies, post-harvest disorders, and inconsistent fruit quality in apples like “Honeycrisp”. Washington State University released a new apple cultivar, called “WA38”, in 2017. Limited literature is available about the productive characteristics of this new cultivar. An experimental trial evaluating the effect of crop load on leaf area, fruit quality, mineral composition, and return bloom of “WA 38” was conducted for two consecutive years (2017 and 2018) to determine an optimal crop load. Trees were trained as a spindle and grafted on Malling-9 Nic29 (Nic29) rootstocks. Crop loads were adjusted to 2, 4, 6, and 8 fruits/cm2 of trunk cross-sectional area (TCSA). Crop load had a significant effect on production, with yields ranging from 28 to 83 MT/ha in 2017. Fruit quality was impacted by increasing crop load, with a reduction in fruit weight, soluble solid content, firmness, dry matter, titratable acidity, and a delay in maturity. Leaf-to-fruit ratios were higher in lower crop loads. Relatively consistent flower bud formation was seen at the 6 and 8 fruits/cm2 categories. A possible threshold for optimal fruit quality and consistent bloom was identified around 6 fruits/cm2 TCSA.

Rootstock and Nutrient Imbalance Leads to ‘‘Green Spot’’ Development in ‘WA 38’ Apples

“…Based on fruit weight, diameter, and fruit number per tree, the estimated yield per hectare in the experimental block was %59 and 58 tons on 'M.9', and 40 and 48 tons on 'G.41' in 2018 and 2019, respectively, considering a tree density of 3025 trees per hectare. These results are within the same range reported by Brendon et al (2019) of 28 to 88 tons per hectare for equivalent crop load [2.1 fruit per cm 2 trunk cross-sectional area (TCSA)].…”

“…Fruit weight ranged between 262 and 302 g, and according to Washington Apple Commission standards, these fruits correspond to a box size between 72 and 64 (number of apples in a 40-lb carton box), considered a large-size apple. Fruit count, diameter, and weight are equivalent to those previously reported by Brendon et al (2019) and Gomez and Kalcsits (2020) for 'WA 38' apples. Gomez and Kalcsits (2020) reported an average fruit weight of 310 ± 11 g and fruit diameter of 87.7 ± 1.28 mm on a fourth leaf 'WA 38' grown on 'M.9-337', and fruit count of 61 fruit per tree.…”

Modelling Soluble Solids Content Accumulation in ‘Braeburn’ Apples

“…The effects of field treatments and physiological differences were directly related to the developmental stage of the fruit. Differences in tree sector position and crop load [ 1 , 38 ] caused increasingly large differences in SSC during fruit development and negligible differences due to early season temperature ( 2 C to ambient). Differences in sector position influence SSC early in the season whereas crop load effects increase steadily during fruit development.…”

Effects of Different Crop Loads on Physiological, Yield and Fruit Quality of ‘JoyaTM’ Apple Trees: High Crop Load Decreases Maximum Daily Trunk Diameter and Does Not Affect Stem Water Potential

“…However, fruit size, acidity and SSC decreased. Crop load management is one of the most crucial vital practices determining the yield and fruit quality in fruit tree orchards (Anthony et al, 2019). Low crop load levels do not increase fruit size, beyond a saturation point (Corelli-Grappadelli and Lakso, 2004).…”