D. H. Simons

Lychee (Litchi chinensis Sonn.) pericarp desiccation and the importance of postharvest micro-cracking

Abstract Lychee fruit are prone to postharvest desiccation, resulting in browning of the pericarp. Microscopic cracks (20–100 μm wide) in the pericarp surface were observed at harvest and had significantly increasing in density 12 h later. Microcracking extended through the sub-epidermal sclerenchyma layer into the mesocarp. Pericarp desiccation occurred prior to crack development, with cracking the result of dehydration rather than the initial cause. No evidence of cuticle thinning was observed prior to micro-cracking, however, localised cuticle deterioration on the protuberance did occur. We believe that initial pericarp desiccation may be the result of high permeability of the cuticle to water vapour, cuticle damage and the presence of lenticels. Although the cracking did not increase the rate of desiccation, micro-cracks may be important in both exposing the underlying anthocyanin-containing mesocarp tissue to further desiccation, and fungal penetration into the pericarp.

Effects of low oxygen and high carbon dioxide on tomato cultivar 'Bermuda' fruit physiology and composition

Abstract Breaker stage tomatoes (Lycopersicon esculentum Mill., cultivar ‘Bermuda’) were treated in air, 0.5% or 1.0% oxygen (O2) in nitrogen (N2) or 80% carbon dioxide (CO2) in air for 1, 3, 5 or 7 days at 22 °C. A 1 day low O2 treatment delayed ripening after treatment by 1–2 days compared to a ripening period of 4 days for the control; elevated CO2 for 1 day had no effect on ripening after treatment. Low O2 increased production of ethanol and acetaldehyde compared to the control and high CO2. Fruit treated for 3 or more days in low O2 or high CO2 showed skin injury and blotchy ripening. Disease incidence increased with treatment time, but could be controlled in 1 day treatments by reducing relative humidity to about 70%. Firmness, total soluble solids, titratable acidity and pH of pericarp and gel of 1 day treated fruit were not different from the control.

Involvement of ethylene in postharvest senescence of Boronia heterophylla flowers

Treatment of cut flowering Boronia heterophylla (red boronia) stems with 10 mu L ethylene/L for 72 h at 20 degrees C induced flower senescence and abscission, and thereby reduced stem fresh weight and vase life. Pretreatment with 1-methylcyclopropene (1-MCP) reduced these ethylene effects. Treatment of B. heterophylla with 10 mu L ethylene/l for a shorter 12 h period at 20 degrees C did not affect vase life. Rates of endogenous ethylene production by B. heterophylla flowers increased in association with wilting during flower senescence.

Use of 1-Methylcyclopropene to Modulate Banana Ripening

Premature and rapid ripening are two ethylene-related postharvest problems of banana fruit. Ethylene binding inhibitors such as diazocyclopentadiene (DACP) delay fruit ripening, even when applied at late stages [2]. However, constraints prohibit commercial use of DACP [2]. 1-Methylcyclopropene (1-MCP), an alternative and irreversible ethylene binding inhibitor, prevents fruit ripening [1]. This study investigated effects of 1-MCP applied before or after ethylene gasing.

Alternaria alternata causes petal blight and flower drop in harvested Geraldton waxflower

Six isolates of Altemaria alternata were tested and shown to be pathogenic on detached flowers of Geraldton waxflower cv. Alba. The fungus caused petal blight and abscission ofthe pedicel from inoculated flowers. This finding strengthens the hypothesis that fungal infection of Geraldton waxflower flowers commonly leads to premature flower drop. Furthermore, it shows that, in addition to Bohytis cinerea, which has been shown previously to cause flower abscission, A. alternata can also cause flower abscission.

Calcium treatment of harvested Geraldton waxflower does not enhance postharvest quality

Postharvest flower abscission from cut Geraldton waxflower (Chamelaucium uncinatum) is mostly caused by fungal invasion. Elevated plant tissue calcium concentrations through postharvest application reduces fungal disease severity in various crops. Such results may be explained by strengthening of plant cell walls by calcium. Strengthening provides a structural barrier to fungal hyphae, thereby restricting invasion of plant cells. Postharvest pulsing with calcium solution substantially increased calcium concentrations in waxflower tissues. Ca-45 tracer revealed calcium distribution throughout flowering sprigs, including infection sites such as stylar tissue. However, pulsing waxflower sprigs with calcium did not suppress either disease or flower abscission, nor did it enhance vase life.