Identifying factors that contribute to mango resin canal discolouration

Resin canal discolouration (RCD) is a quality defect that reduces the market value of ripe mango fruit. Market reports of RCD have increased during the past two mango seasons, particularly for early-season ‘Kensington Pride’ fruit produced near Darwin in the Northern Territory. A 1-year project was undertaken during the 2013 mango season to start identifying possible factors that contribute to RCD. The research focused on ‘Kensington Pride’ fruit produced in the Darwin production area. The research team monitored fruit from orchard to market, conducted specific trials, and completed detailed scientific evaluation of affected fruit. Preliminary findings suggest that RCD: • Can also occasionally be found in green fruit on the tree or at grading but only when the fruit or stems have severe physical injury or pathogen infection. • Occurrence can vary considerably between different orchards and for different harvest dates. • Increases in severity as fruit develop from firm ripe to overripe. • Incidence is higher in fruit that are exposed to commercial handling procedures than those ripened directly off the tree. • Can be present in the flesh without symptoms being exhibited on the skin. • Incidence can be higher in early-season fruit than those picked later. • Incidence can be higher in fruit harvested soon after a rain event. • Symptoms may be associated with bacterial infection. The observations to-date suggest that RCD is likely to occur when field conditions result in the production of ‘sensitive’ fruit that, in turn, express the defect when exposed to the common harvest and postharvest stresses. Follow-on R&D will aim to confirm the causes of RCD and to develop reliable control measures

Reducing skin damage and improving postharvest efficiency of Calypso mango

‘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

1-Methylcyclopropene treatment efficacy in preventing ethylene perception in banana fruit and grevillea and waxflower flowers

Premature ripening and/or senescence and abscission induced by exposure to ethylene are significant postharvest problems. Banana fruit and grevillea and Geraldton waxflower flowers are among affected commodities. Treatment with 1-methylcyclopropene gas or silver thiosulfate liquid can be used to prevent ethylene perception and response. Treatment of banana fruit with 10 nL 1-methylcyclopropene/L for 12 h at 20˚C afforded protection against subsequent serial treatments over 13 days of subsets with 100 L ethylene/L for 24 h at 20˚C. Protection of Grevillea ‘Sylvia’ inflorescences was effective only for 2 days. Thereafter, fruit and inflorescences regained sensitivity to ethylene. In contrast, neither banana fruit nor grevillea inflorescences treated with 10 nL 1-methylcyclopropene/L for 12 h at 2˚C were protected against ethylene. 1-Methylcyclopropene binding to ethylene receptors was apparently not achieved at the lower temperature. Increasing the 1-methylcyclopropene concentration to 100 nL/L, applied at 2.5˚C to banana fruit, achieved protection against ethylene. Waxflower sprigs treated with 10 nL 1-methylcyclopropene/L for 12 h at 2 or 20˚C regained full sensitivity to ethylene after about 2 and 4 days, respectively. In contrast, pulsing waxflower with 0.5 mmol Ag+/L as silver thiosulfate for 12 h at 2 or 20˚C afforded protection against ethylene for the 10 days duration of the experiment

Anatomy of ethylene-induced floral-organ abscission in Chamelaucium uncinatum (Myrtaceae)

Postharvest abscission of Geraldton waxflower (Chamelaucium uncinatum Schauer) flower buds and flowers is ethylene-mediated. Exposure of floral organs to exogenous ethylene (1 mu L L-1) for 6 h at 20 degrees C induced separation at a morphologically and anatomically distinct abscission zone between the pedicel and. oral tube. Flower buds with opening petals and flowers with a nectiferous hypanthium were generally more responsive to exogenous ethylene than were flower buds enclosed in shiny bracteoles and aged (senescing) flowers. The anatomy of abscission-zone cells did not change at sequential stages of floral development from immature buds to aged flowers. The zone comprised a layer of small, laterally elongated-to-rounded, closely packed and highly protoplasmic parenchyma cells. Abscission occurred at a two- to four-cell-wide separation layer within the abscission zone. The process involved degradation of the middle lamella between separation layer cells. Following abscission, cells on both the proximal and distal faces of the separation layer became spherical, loosely packed and contained degenerating protoplasm. Central vascular tissues within the surrounding band of separation layer cells became torn and fractured. For flower buds, bracteoles that enclose the immature floral tube also separated at an abscission zone. However, this secondary abscission zone appeared less sensitive to ethylene than the primary ( central). oral-tube abscission zone as bracteoles generally only completely abscised when exposed to 10 mu L L-1 ethylene for the longer period of 24 h at 20 degrees C. The smooth surfaces of abscised separation-layer cells suggest that hydrolase enzymes degrade the middle lamella between adjacent cell walls

Extension of the shelf life of banana fruit by 1-methylcyclopropene in combination with polyethylene bags

The effect of the new anti-ethylene compound 1-methylcyclopropene (1-MCP) in combination with polyethylene bags on the ripening of harvested banana fruit was investigated. 1-MCP treatment delayed peel colour change and fruit softening, and extended shelf life in association with suppression of respiration and C2H4 evolution. Banana fruit ripening was delayed when exposed to 0.01-1.0 mu l 1-MCP/l for 24 h, and increasing concentrations of 1-MCP were generally more effective for longer periods of time. Similar results were obtained with fruit sealed in polyethylene bags (0.03 mm thick) containing 1-MCP at various concentrations, but longer delays in ripening were achieved. The greatest longevity of about 58 days was realised by packing fruit in sealed polyethylene bags with 1-MCP at either of 0.5 or 1.0 mu l/l. Analyses of C2H4 and CO2 concentrations within polyethylene bags confirmed that 1-MCP suppressed both C2H4 evolution and respiration. Thus, application of 1-MCP in combination with the use of polyethylene bags can greatly extend the postharvest life of banana fruit. (C) 1999 Elsevier Science B.V. All rights reserved