Effect of hand fruit thinning and harvest time on colour development of ‘Hass’ avocado fruit during ripening

Fruit quality and source-sink relationships are influenced by crop load. However, less is known about its effect on ‘Hass’ avocado fruit during ripening. This study aimed to examine the influence of crop load on the development of the exocarp colour of ‘Hass’ avocado fruit during ripening at three harvest times (early, mid, and late harvest). Three levels of crop load adjustments were applied: high load (100%), moderate load (50%) and low load (25%). After each harvest time (early, mid- and late), fruit were stored at 5.5°C for 28 d thereafter, ripened at 25°C for 4 d and evaluated for fruit firmness, visual colour and objective colour parameters (lightness-L*, chroma-C* and hue angle-h°), total chlorophyll, total anthocyanin and cyanidin-3-O-glucoside. Firmness was greatest for fruit from low loads, followed by moderate after 4 d at 25°C during mid- and late harvest. Firmness loss was positively correlated with L* (r=0.887), C* (r=0.882), h° (r=0.762) and negatively correlated with visual colour (r=-0.799). Low and moderate crop load adjustment during early and mid-harvests led to improved colour after 4 d. The effects of crop load on the visual colour of late harvest fruit were not significant. In early and middle harvests, total chlorophyll and carotenoids declined rapidly in low load fruit compared to moderate and high loads. We observed higher anthocyanin and cyanidin-3-O-glucoside concentrations at day 4 with low load followed by moderate load fruit. In summary, low (25%) and moderate (50%) fruit thinning improved colour development of ‘Hass’ avocado fruit during early and middle harvest.