Relationship of on-tree fruit colour change to maturity and postharvest behaviour of Lamb-Hass avocado fruit
The Lamb Hass avocado cultivar has a unique behaviour of preharvest skin colour blackening, while some fruit remains green on the same tree. This results in fruit skin colour variation at harvest, a phenomenon also perceived as uneven ripening. This study evaluated the relationship of on-tree fruit colour change to harvest maturity and postharvest performance of Lamb Hass avocado fruit. Mid-season Lamb Hass avocado fruit were harvested from inside and outside canopy positions during the 2017/2018 growing season at Everdon Estates. The fruit from each canopy were grouped into two skin colour categories: green and blackening, and sorted according to fruit size (small, medium, and large). Fruit were analysed for maturity at harvest, stored for 28 days at 5.5°C; 90±5% relative humidity, and moved to 20°C for 7 days for postharvest behaviour and quality evaluation. Quality parameters evaluated included mass loss (%), fruit colour changes and non-structural carbohydrates. Mesocarp dry matter (DM) was highly influenced (p<0.001) by fruit colour, with the blackening fruit having higher DM content (29.31%) while the lowest DM content (26.13%) was recorded for green-skinned fruit. With the higher maturity of blackening fruit, significant compositional differences were detected between the fruit; blackening fruit showed a lower concentration of the C7 sugar, mannoheptulose (0.30 mg g‑1), than the greener fruit (0.35 mg g‑1). In addition, the rate at which the stored carbohydrates were used up was significantly higher for the blackening fruit than the greener fruit. Significant differences in exocarp colour variables were observed at harvest, with the blackening fruit having significantly lower values of the colour parameters; lightness (L*), chroma (C*) and hue angle (h°). This confirms the initiation of fruit darkening on the tree; however, the studied fruit were found to be statistically similar (p>0.05) in colour during shelf life, which indicates that avocado ripening suppresses fruit colour variation observed at harvest. Additionally, the blackening fruit had a higher mass loss rate (3.44%) than the green-skinned fruit (2.92%); this indicates that the blackening fruit ripened faster than the greener fruit. Fruit size significantly influenced fruit colour change; larger fruit were darker than the smaller fruit at harvest. The outcome of the study demonstrated that fruit colour change on the tree contributes significantly to Lamb Hass uneven ripening.
Mwelase, S., Mditshwa, A., Magwaza, L.S. and Tesfay, S.Z. (2022). Relationship of on-tree fruit colour change to maturity and postharvest behaviour of Lamb-Hass avocado fruit. Acta Hortic. 1349, 95-104
avocado maturity, dry matter content, uneven ripening, fruit colour