Effect of crop load management and canopy architecture on yield and fruit quality of late-season plum 'Angeleno'

The Australian summer fruit industry has identified that sales growth is impeded by low consumer satisfaction with fruit quality, leading to low prices and static consumption. Crop load is known to affect fruit size of plum, but few studies have been reported on fruit quality. The effect of crop load on fruit quality was studied in an experimental orchard at Tatura, Australia. The objective of the study was to identify crop load management practices, under Tatura trellis and vase training systems, to enable plum to maximise uniformity in fruit quality attributes. Different thinning regimes were implemented in season 2016/17 to establish the following crop load treatments: 1) high: minimally thinned; 2) medium (commercial standard as control): moderately thinned and; 3) low: heavily thinned. Larger canopies occurred on Tatura trellis compared to vase, despite identical tree density and age. Larger tree size was reflected in trunk cross-sectional area and canopy radiation interception (f_PAR), providing capacity to support greater fruiting levels and high yields. Mid-season f_PAR was ~68% under Tatura Trellis compared to ~52% for vase trees. Fruiting level did not affect full bloom date in spring 2016 and spring 2017 or f_PAR in summer 2017 for a given canopy architecture. However, trunk growth was higher under low crop load on Tatura trellis. Overall, high cropping levels reduced fruit weight and lowered pack-out performance. Irrespective of training and cropping level combination, fruit sweetness was high (≥17.2 °Brix), with low variability (CV≤11%). Over half of all fruit grown on Tatura trellis exceeded 18 °Brix, compared to ≤38% on vase. For vase trained trees, fruit maturity and firmness were similar across crop load treatments. However, for Tatura trellis training system, high cropping levels produced more immature and firmer fruit.