Reducing skin damage and improving postharvest efficiency of Calypso mango

Abstract

‘B74’ mango (marketed as CalypsoTM) was bred at Childers in subtropical Queensland specifically to overcome the inconsistent production of the cultivar ‘Kensington Pride’. Ongoing research is maximising its genetic potential in the main production regions.
‘B74’ mango fruit develops an attractive blush during growth and a full yellow skin colour when ripe, but small spots from damaged lenticels often appear on the skin. This affects the visual appeal but does not affect the flesh; nevertheless the value of the fruit is reduced.
The project confirmed that fruit can have less LD if they are grown in hotter production, are smaller and more mature, have more blush, and are from trees that had more uniform flowering or smaller canopy area. However, these parameters accounted for only 32-35% of the variation in LD. Not irrigating the trees for 3-8 weeks before harvest may “dry” the fruit out and make them more resistant to LD but this was not observed. ‘B74’ is more prone to this lenticel discolouration (LD) than most other Australian mango cultivars, most likely because it has 3-4 times higher lenticel density on the fruit surface at harvest.
LD is worse when the fruit are exposed to water either from rain or during harvesting. In order to reduce contact with water, the fruit were paper bagged (done commercially in apple and other fruit in Japan), or sprayed with a carnauba-based wax, two months or several days before harvest, respectively. Both treatments reduced LD in the ripe fruit. Bagging is labourintensive but may be profitable for high value markets, and wax sprays need commercial testing with whole tree spraying.
LD is likely due to an oxidation reaction, similar to when cut apple turns brown. Reducing oxygen around or in the fruit, or using anti-oxidants may reduce the browning reaction. However, holding the fruit in plastic bags, fruit coatings and antioxidant dips before ripening had either no effect. The most promising approaches were eliminating water from the harvesting and packing procedures, and irradiating fruit for export when they were about three days from ripe. Both approaches add extra challenges to the harvest-to-consumer chain, but they may have application is certain circumstances.
Mango fruit need to be harvested within 2-4 weeks of reaching minimum maturity to prevent fruit from falling from the tree. This short harvest window results in challenges with picking teams and equipment. Trials attempted to induce earlier or later flowering the spread the harvest window in the hotter production areas. Trials with Ethephon® sprays indicated its potential to stimulate earlier flowering. Removing flowers in the Katherine environment to encourage the trees to re-flower was unsuccessful.
The ability to ripen fruit in transit from farm to market will reduce energy costs and infrastructure requirements in market. Commercial tests indicated that the newer 12 m rail containers can retain ‘B74’ fruit temperatures at about 18ºC, and several systems to manage carbon dioxide and ethylene concentrations (both important in fruit ripening) can be controlled.