Girdling as a tool to unravelling the ‘Hass’ avocado skin color problem
Skin color change problems have been reported by overseas markets to the South African Avocado Growers Association (SAAGA) board. The problem has been associated with chilling damage during cold storage of early harvested fruit, possibly related to the maturity stage at harvest. Girdling around the tree cambium is used to restrict basipetal movement of photosynthates, resulting in accumulation of assimilates above the girdled position. Increased fruit assimilates have been considered to improve fruit quality. Therefore, the aim of this study was to evaluate the effect of tree girdling and harvest time on ‘Hass’ avocado fruit color change. Avocado fruit were harvested from two geographic locations (Limpopo and Mpumalanga), during the early and middle season, at an orchard block with a slope (upper and lower slope positions), from girdled and non-girdled trees. After harvest, fruit were then immediately transported to the Agricultural Research Council-Institute for Tropical and Subtropical Crops (ARC-ITSC) postharvest laboratory for storage and analysis. At the laboratory, fruit were sorted and graded manually (3 replicates of 30 fruits replicate-1), and then stored at 5.5°C for 28 days. Thereafter fruit were withdrawn from cold storage and ripened at 21°C. During ripening, avocado fruit were evaluated for chilling damage, firmness, subjective (by eye) and objective (L, C and hue measured with a chroma meter) skin color, and pathological and physiological damage. Generally, girdling had a negative impact on fruit quality. Poor skin color development was observed (±70% color change) for fruit from both production regions for both harvest times. Further, higher chilling damage was observed on fruit from girdled trees than on those from control trees during the early harvest season, 75 and 62%, respectively. Overall improved internal quality was observed on fruit harvested during the middle harvest from both girdled and non-girdled trees. Tree girdling had no effect on ‘Hass’ avocado fruit skin color development. However, harvest time had a positive effect on color developent and fruit quality.
Sakhile Mathe won an ISHS Young Minds Award for the best poster presentation at the I International Symposium on Avocado at IHC2018 in Turkey in August 2018.
Sakhile Mathe, ARC-ITSC, 3 River Street, 1200 Nelspruit, South Africa, e-mail: email@example.com