Postharvest factors affect under-skin browning in 'Honey Gold' mango fruit

BACKGROUND

Under-Skin Browning (USB) is a physiological skin disorder that significantly reduces quality of 'Honey Gold' mango (HG) fruit. Relationships between potential causative factors (vibration, holding temperature, sap) and expression factors (enzymes activities, phenolic concentration, anatomy) were investigated.

RESULTS

USB incidence was 2.6-3.6-fold higher in ripe HG fruit vibrated for 3-18 h at 12 °C to simulate transport damage and held then at 12 °C for 8 days compared to control fruit held under the same conditions. USB severity of fruit lightly abraded with sand paper to simulate physical damage and artificially induce USB was higher in fruit held at 10 °C than at 6-8 °C or 12-13 °C for 6-8 days. Compared to non-affected skin, USB-affected tissue had a 7.4% increase in total phenolics concentration. However, polyphenol oxidase (PPO) and peroxidase (POD) activities decreased by 19%. Anatomical similarities were observed between USB symptoms and sapburn caused by spurt sap or terpinolene (a major sap component) to abraded skin areas. Incidence of sapburn was higher in abraded fruit held at 12 °C than at 20 °C.

CONCLUSION

Holding HG mango fruit at 10 °C can intensify USB. Activities of PPO and POD appear not to be regulatory factors in USB expression in HG. Sap components may be involved in USB expression under conducive postharvest conditions. © 2021 Society of Chemical Industry.

Diurnal Harvest Cycle and Sap Composition Affect Under-Skin Browning in 'Honey Gold' Mango Fruit

Under-skin browning (USB) is an unsightly physiological disorder that afflicts 'Honey Gold' mango fruit. Under-skin browning symptoms develop after harvest upon the interaction of physical abrasion and physiological chilling stresses. Less understood preharvest and/or harvest factors may also influence fruit susceptibility to USB. In this study, we examined the impact of harvest time during the diurnal cycle and fruit sap components on USB development. Fruits were harvested at 4- to 6-h intervals, lightly abraded with sandpaper to simulate vibration damage during refrigerated road transport, held at 12 ± 1°C for 6 days, transported to the research facilities and ripened before USB assessment. Spurt and ooze sap from the fruit were collected at each harvest time. The samples were separated and analysed by gas chromatography-mass spectrometry. Fruit harvested at 10:00, 14:00 and 18:00 h had 3- to 5-fold higher incidence of USB than did those picked at 22:00, 2:00 and 6:00 h. Sap concentrations of the key aroma volatile compounds 2-carene, 3-carene, α-terpinene, p-cymene, limonene and α-terpinolene were higher for fruit harvested at 14:00 h compared to those picked at other times. In the fruits harvested in the afternoon, abraded skin treated with spurt sap sampled at 14:00 h had 14.3- and 29.0-fold higher incidence and severity, respectively, of induced browning than did those treated with sap collected at 6:00 h. The results showed that fruit harvested in the afternoon were more susceptible to USB than those picked at night or in early morning. The diurnal variation in fruit sensitivity was evidently associated with specific compositional differences in sap phytotoxicity. Topical application to the fruit skin of pure terpinolene and limonene resulted in induced USB damage, whereas pure carene and distilled water did not. Microscopy examination showed that while skin damage caused by pure terpinolene and limonene was not identical to USB per se, similarities suggested that sap components cause USB under inductive commercial conditions. Considered collectively, these findings suggest that night and early morning harvesting will reduce USB and thus improve the postharvest quality of Honey Gold mango fruit.

POMICS: A Simulation Disease Model for Timing Fungicide Applications in Management of Powdery Mildew of Cucurbits

A weather-based simulation model, called Powdery Mildew of Cucurbits Simulation (POMICS), was constructed to predict fungicide application scheduling to manage powdery mildew of cucurbits. The model was developed on the principle that conditions favorable for Podosphaera xanthii, a causal pathogen of this crop disease, generate a number of infection cycles in a single growing season. The model consists of two components that (i) simulate the disease progression of P. xanthii in secondary infection cycles under natural conditions and (ii) predict the disease severity with application of fungicides at any recurrent disease cycles. The underlying environmental factors associated with P. xanthii infection were quantified from laboratory and field studies, and also gathered from literature. The performance of the POMICS model when validated with two datasets of uncontrolled natural infection was good (the mean difference between simulated and observed disease severity on a scale of 0 to 5 was 0.02 and 0.05). In simulations, POMICS was able to predict high- and low-risk disease alerts. Furthermore, the predicted disease severity was responsive to the number of fungicide applications. Such responsiveness indicates that the model has the potential to be used as a tool to guide the scheduling of judicious fungicide applications.

Stable isotope dilution assay (SIDA) and HS-SPME-GCMS quantification of key aroma volatiles for fruit and sap of Australian mango cultivars

Reported herein is a high throughput method to quantify in a single analysis the key volatiles that contribute to the aroma of commercially significant mango cultivars grown in Australia. The method constitutes stable isotope dilution analysis (SIDA) in conjunction with headspace (HS) solid-phase microextraction (SPME) coupled with gas-chromatography mass spectrometry (GCMS). Deuterium labelled analogues of the target analytes were either purchased commercially or synthesised for use as internal standards. Seven volatiles, hexanal, 3-carene, α-terpinene, p-cymene, limonene, α-terpinolene and ethyl octanoate, were targeted. The resulting calibration functions had determination coefficients (R²) ranging from 0.93775 to 0.99741. High recovery efficiencies for spiked mango samples were also achieved. The method was applied to identify the key aroma volatile compounds produced by 'Kensington Pride' and 'B74' mango fruit and by 'Honey Gold' mango sap. This method represents a marked improvement over current methods for detecting and measuring concentrations of mango fruit and sap volatiles.

Characterisation of betalain biosynthesis in Parakeelya flowers identifies the key biosynthetic gene DOD as belonging to an expanded LigB gene family that is conserved in betalain-producing species

Plant betalain pigments are intriguing because they are restricted to the Caryophyllales and are mutually exclusive with the more common anthocyanins. However, betalain biosynthesis is poorly understood compared to that of anthocyanins. In this study, betalain production and betalain-related genes were characterized in Parakeelya mirabilis (Montiaceae). RT-PCR and transcriptomics identified three sequences related to the key biosynthetic enzyme Dopa 4,5-dioxgenase (DOD). In addition to a LigB gene similar to that of non-Caryophyllales species (Class I genes), two other P. mirabilis LigB genes were found (DOD and DOD-like, termed Class II). PmDOD and PmDOD-like had 70% amino acid identity. Only PmDOD was implicated in betalain synthesis based on transient assays of enzyme activity and correlation of transcript abundance to spatio-temporal betalain accumulation. The role of PmDOD-like remains unknown. The striking pigment patterning of the flowers was due to distinct zones of red betacyanin and yellow betaxanthin production. The major betacyanin was the unglycosylated betanidin rather than the commonly found glycosides, an occurrence for which there are a few previous reports. The white petal zones lacked pigment but had DOD activity suggesting alternate regulation of the pathway in this tissue. DOD and DOD-like sequences were also identified in other betalain-producing species but not in examples of anthocyanin-producing Caryophyllales or non-Caryophyllales species. A Class I LigB sequence from the anthocyanin-producing Caryophyllaceae species Dianthus superbus and two DOD-like sequences from the Amaranthaceae species Beta vulgaris and Ptilotus spp. did not show DOD activity in the transient assay. The additional sequences suggests that DOD is part of a larger LigB gene family in betalain-producing Caryophyllales taxa, and the tandem genomic arrangement of two of the three B. vulgaris LigB genes suggests the involvement of duplication in the gene family evolution.

Cu2+ inhibition of gel secretion in the xylem and its potential implications for water uptake of cut Acacia holosericea stems

Maintaining a high rate of water uptake is crucial for maximum longevity of cut stems. Physiological gel/tylosis formation decreases water transport efficiency in the xylem. The primary mechanism of action for post-harvest Cu(2+) treatments in improving cut flower and foliage longevity has been elusive. The effect of Cu(2+) on wound-induced xylem vessel occlusion was investigated for Acacia holosericea A. Cunn. ex G. Don. Experiments were conducted using a Cu(2+) pulse (5 h, 2.2 mM) and a Cu(2+) vase solution (0.5 mM) vs a deionized water (DIW) control. Development of xylem blockage in the stem-end region 10 mm proximal to the wounded stem surface was examined over 21 days by light and transmission electron microscopy. Xylem vessels of stems stood into DIW were occluded with gels secreted into vessel lumens via pits from surrounding axial parenchyma cells. Gel secretion was initiated within 1-2 days post-wounding and gels were detected in the xylem from day 3. In contrast, Cu(2+) treatments disrupted the surrounding parenchyma cells, thereby inhibiting gel secretion and maintaining the vessel lumens devoid of occlusions. The Cu(2+) treatments significantly improved water uptake by the cut stems as compared to the control.

The role of 1-methylcyclopropene in lignification and expansin gene expression in peeled water bamboo shoot (Zizania caduciflora L.)

BACKGROUND

Water bamboo shoot (WBS) (Zizania caduciflora L.) is a fleshy aquatic vegetable susceptible to lignification. In this study, effects of 1-methylcyclopropene (1-MCP) anti-ethylene treatment on lignification of harvested peeled WBS were investigated.

RESULTS

Peeled shoots were treated with 0.5 µL L(-1) 1-MCP for 20 h at 20 °C and then stored at 20 °C for up to 9 days. Sensory quality, lignin content and activities of the lignification-associated enzymes peroxidase (POD) and phenylalanine ammonia lyase (PAL) were evaluated. Expression of expansin (ZcExp) was also assessed. 1-MCP application maintained better sensory quality and inhibited the increase in lignin content. Lessened lignification was associated with reduced activities of POD and PAL. Moreover, 1-MCP-treated shoots showed lower expression of the ZcExp gene.

CONCLUSION

1-MCP pretreatment suppressed the synthesis of lignin and thereby delayed lignification in peeled WBS.

Characterisation of xylem conduits and their possible role in limiting the vase life of cut Acacia holosericea (Mimosaceae) foliage stems

Early desiccation limits the vase life of Acacia cut flowers and foliage and may be attributable to poor hydraulic conductivity (Kh) of the cut stems. Acacia holosericea A.Cunn. ex G.Don has been adopted as the test species to investigate the postharvest water relations of the genus Acacia. To understand potential constraints on Kh, xylem conduits in cut A. holosericea stems were anatomically characterised by light and scanning and transmission electron microscopy. Vessels with simple perforation plates and tracheids were the principal water conducting cells. Bordered vestured intervessel pits were present in xylem vessel elements. The majority of conduits (89%) were short at 1-5cm long. Only 2% were 15-16cm in length. Mean xylem conduit diameter was 77±0.9µm and the diameter profile showed a normal distribution, with 29% of diameters in the range of 70-80µm. Simple perforation plates can offer relatively low resistance to water flow. On the other hand, bordered vestured pits and short xylem conduits can confer comparatively high resistance to water flow. Overall, the presence of bordered vestured pits, together with a high proportion of short xylem conduits and high stomatal densities (232±2mm-2) on unifacial phyllodes, could contribute to early dehydration of A. holosericea cut foliage stems standing in vase water. Further research will relate these anatomical features with changes in Kh and transpiration of cut foliage stems.

Role of phenylalanine ammonia-lyase in heat pretreatment-induced chilling tolerance in banana fruit

Increasing evidence suggests that phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) is associated with low temperature stress in plant tissues. Banana fruit are highly susceptible to chilling injury. However, little is known about the role of PAL (i.e. gene expression, protein level and activity) in fruit chilling. In this work, the involvement of PAL induced by heat treatment (38 degrees C for 3 days) prior to storage (8 degrees C) in chilling tolerance was investigated. The PAL inhibitor 2-aminoindan-2-phosphonic acid (AIP) was also used to further study the role of PAL in the chilling tolerance. The results showed that mRNA transcripts (MaPAL1 and MaPAL2) and PAL protein levels increased during storage at chilling temperature. Heat treatment prior to storage alleviated chilling injury and enhanced PAL activity, protein amount and MaPAL1 and MaPAL2 transcript levels. The increases in parameters of PAL upon heat pretreatment were all inhibited by AIP treatment, which resulted in aggravation of chilling injury. Thus, these findings indicate that the induction of PAL by heat pretreatment was regulated at both the transcriptional and the translational levels and that PAL may play a role in heat pretreatment-induced chilling tolerance of banana fruit.

1H-Nuclear magnetic resonance imaging of ripening 'Kensington Pride' mango fruit

Physicochemical gradients occur in mango mesocarp tissue during ripening. These gradients are reflected in water activity, which is non-uniform throughout the mesocarp. Signal intensity in proton magnetic resonance images (first echo, proton density and T2) for green-mature `Kensington Pride' mesocarp tissue was highest near the endocarp and lowest near the exocarp. Relative signal intensity increased in the middle mesocarp as ripening proceeded, but remained relatively low in the outer mesocarp. T2 relaxation times for inner and middle mesocarp regions fell during ripening. The data suggest that water activity in the mesocarp tissue increased in an outward-moving flux as ripening progressed. This change in water activity was associated with starch hydrolysis and other ripening-related processes that commence near the endocarp.

Effect of Abscisic Acid on Banana Fruit Ripening in Relation to the Role of Ethylene

The role of abscisic acid (ABA) in banana fruit ripening was examined with the ethylene binding inhibitor, 1-methylcyclopropene (1-MCP). ABA (0, 10(-5), 10(-4), or 10(-3) mol/L) was applied by vacuum infiltration into fruit. 1-MCP (1 µL/L) was applied by injecting a measured volume of stock gas into sealed glass jars containing fruit. Fruit ripening, as judged by ethylene evolution and respiration associated with color change and softening, was accelerated by 10(-4) or 10(-3) mol/L ABA. ABA at 10(-5) mol/L had no effect. The acceleration of ripening by ABA was greater at 10(-3) mol/L than at 10(-4) mol/L. ABA-induced acceleration of banana fruit ripening was not observed in 1-MCP treated fruit, especially when ABA was applied after exposure to 1-MCP. Thus, ABA's promotion of ripening in intact banana fruit is at least partially mediated by ethylene. Exposure of ABA-treated fruit to 0.1 µL/L ethylene for 24 h resulted in increased ethylene production and respiration, and associated skin color change and fruit softening. Control fruit (no ABA) was unresponsive to similar ethylene treatments. The data suggest that ABA facilitates initiation and progress in the sequence of ethylene-mediated ripening events, possibly by enhancing the sensitivity to ethylene.

Effect of delayed film wrapping and waxing on the shelf life of avocado fruit

Film wrapping and waxing are both known to extend the shelf life of harvested avocado fruit. However, the effect of delays in film wrapping and waxing on shelf life has not been reported. Early, mid, and late season avocado cv. Hass fruit were wrapped in 'Glad Wrap' or waxed in 'Avocado and Passion-fruit Wax' at intervals of up to 96 h after harvest. Compared with untreated control fruit, both wrapping and waxing delayed softening and colour change at 22�C by about 50%. Loss in fruit weight during ripening was reduced more by wrapping than by waxing. Delaying wrapping or waxing by up to 48 h after harvest was not associated with consistent differences in shelf life. There was, however, significant (P<0.05) shortening of both time to colour and time to soften if treatment was delayed to 96 h. Accordingly, wrapping or waxing avocado fruit is advisable within 48 h of harvest to realise maximum treatment benefits. Early colouring within 3-4 days of harvest, but not early softening, was characteristic of late season fruit.

A genetic map of the mouse with 4,006 simple sequence length polymorphisms

We have constructed a genetic map of the mouse genome containing 4,006 simple sequence length polymorphisms (SSLPs). The map provides an average spacing of 0.35 centiMorgans (cM) between markers, corresponding to about 750 kb. Approximately 90% of the genome lies within 1.1 cM of a marker and 99% lies within 2.2 cM. The markers have an average polymorphism rate of 50% in crosses between laboratory strains. The markers are distributed in a relatively uniform fashion across the genome, although some deviations from randomness can be detected. In particular, there is a significant underrepresentation of markers on the X chromosome. This map represents the two-thirds point toward our goal of developing a mouse genetic map containing 6,000 SSLPs.

Postharvest floral organ fall in Geraldton waxflower (Chamelaucium uncinatum Schauer)

Possible reasons for, and prevention of, postharvest floral organ fall in Geraldton waxflower (Chamelaucium unciizatum Schauer) were studied. An 11-kg compression load, equivalent to the lidding of a carton, caused flower fall amounting to 1% of the fresh mass of 420-g bunches. Fungal development also resulted in flower abscission. Healthy flowers produced little ethylene (e.g. 0.05 �L/kg.h), while infected flowers produced much more (e.g. 7.71 �L/kg.h) and were shed. Treatment with fungicide (iprodione + mancozeb) and antiethylene compounds [e.g. silver thiosulfate (STS) pulse, Purafil sorbant] reduced flowerfall in packaged flowers. Cut sprigs which suffered severe water deficit also shed flowers. In cv. Elegance, drying to -3.61 MPa elevated ethylene production (e.g. 1.35 �L/kg . h). Flowerfall induced by water deficit could be reduced by pretreatment with a STS pulse (0.5 mmol Ag+/L for 15-22 h at 0�C or 4 mmol Ag+/L for 20-30 min at about 20�C). Pretreatment with a naphthaleneacetic acid dip (50 mg/L for 1 min at room temperature) shortened the vase life of Elegance.

Effects of ethylene and dehydration on cut flowering stems of Verticordia spp

The potential for ethylene-induced abscission among Verticordia species used for cut flowers (V. nitens, V. chrysantha, V. plumosa, and V. densiflora) was studied by treating them with 2-chloroethyl-phosphonic acid (ethephon) or exposing them to dilute ethylene gas. The possibility that ethylene production induced by water stress may cause flower abscission was also investigated. Dipping in ethephon (500 or 1000 mg/L) failed to induce flower abscission in V chrysantha or V plumosa. Treatment with ethylene (8.6 pL/L) failed to induce flower abscission in V. densiflora. Ethephon and ethylene both induced substantial flower, pedicel, and leaf abscission in V. nitens. Pretreatment with silver thiosulfate prevented ethylene-induced flower abscission in V nitens. Dehydrating stems for periods of 6, 12, 24, or 48 h at about 20�C did not induce flower abscission in either V plunzosa or V nitens. Dehydration periods of 6 and 12 h had no effect on longevity. Longer drying periods (24 and 48 h) induced early loss in appearance (visual quality) of both species.

Transport Properties of the Tomato Fruit Tonoplast : III. Temperature Dependence of Calcium Transport

Calcium transport into tomato (Lycopersicon esculentum Mill, cv Castlemart) fruit tonoplast vesicles was studied. Calcium uptake was stimulated approximately 10-fold by MgATP. Two ATP-dependent Ca(2+) transport activities could be resolved on the basis of sensitivity to nitrate and affinity for Ca(2+). A low affinity Ca(2+) uptake system (K(m) > 200 micromolar) was inhibited by nitrate and ionophores and is thought to represent a tonoplast localized H(+)/Ca(2+) antiport. A high affinity Ca(2+) uptake system (K(m) = 6 micromolar) was not inhibited by nitrate, had reduced sensitivity to ionophores, and appeared to be associated with a population of low density endoplasmic reticulum vesicles that contaminated the tonoplast-enriched membrane fraction. Arrhenius plots of the temperature dependence of Ca(2+) transport in tomato membrane vesicles showed a sharp increase in activation energy at temperatures below 10 to 12 degrees C that was not observed in red beet membrane vesicles. This low temperature effect on tonoplast Ca(2+)/H(+) antiport activity could only by partially ascribed to an effect of low temperature on H(+)-ATPase activity, ATP-dependent H(+) transport, passive H(+) fluxes, or passive Ca(2+) fluxes. These results suggest that low temperature directly affects Ca(2+)/H(+) exchange across the tomato fruit tonoplast, resulting in an apparent change in activation energy for the transport reaction. This could result from a direct effect of temperature on the Ca(2+)/H(+) exchange protein or by an indirect effect of temperature on lipid interactions with the Ca(2+)/H(+) exchange protein.

Role of carbohydrates in diurnal chilling sensitivity of tomato seedlings

Tomato seedlings (Lycopersicon esculentum Mill.) chilled starting at different times during the light/dark cycle were most chilling-sensitive at the end of the dark period (AI King, MS Reid, BD Patterson 1982 Plant Physiol 70: 211-214). Low-temperature tolerance was regained with as little as 10 minutes of light exposure. Low light intensities were less effective than high light intensities in reducing sensitivity, and the length of exposure to light directly influenced sensitivity. Seedlings kept at low night temperatures prior to chilling were also less injured following chilling. Light also restored chilling tolerance to seedlings whose roots were removed. Supplying cut shoots with sucrose, glucose, or fructose reduced chilling sensitivity and largely eliminated the diurnal difference in sensitivity. Endogenous carbohydrate content was correlated with changes in chilling sensitivity; starch and sugar content fell markedly during the dark period. Increased concentrations of sugars were detected 15 minutes after the start of the light period. This evidence all suggests that changes in chilling sensitivity over the diurnal period are regulated by the light cycle. It also suggests that increased sensitivity at the end of the dark period could be due to carbohydrate depletion, and that chilling tolerance following light exposure is likely due to carbohydrate accumulation or closely related events.