Expression of expansin genes during postharvest lignification and softening of ‘Luoyangqing’ and ‘Baisha’ loquat fruit under different storage conditions

Four expansin cDNA fragments, EjEXPA1, EjEXPA2, EjEXPA3 and EjEXPA4, were isolated and characterized from loquat (Eriobotrya japonica Lindl.) fruit. EjEXPA1 mRNA accumulated consistently with the increase in fruit firmness in 0 °C storage of ‘Luoyangqing’ (LYQ) fruit, where chilling injury with increased fruit firmness due to lignification was observed. EjEXPA1 mRNA levels were lower in fruit that underwent low temperature conditioning (LTC, 6 d at 5 °C then 4 d at 0 °C), and in 1-methylcyclopropene (1-MCP) treated fruit, in both cases where chilling injury was alleviated. Fruit of the ‘Baisha’ (BS) cultivar soften after harvest rather than increase in firmness, and high expression levels of EjEXPA1 and EjEXPA4 accompanied the softening of BS fruit stored at 20 °C; such mRNA accumulation was much lower when fruit were stored at 0 °C, where softening was significantly inhibited by the low temperature. Very low expression of EjEXPA2 and EjEXPA3 was observed during storage of both LYQ and BS fruit under the different storage conditions. Our results showed that of the four genes characterized, EjEXPA1 might be associated with chilling-induced lignification while both EjEXPA1 and EjEXPA4 were closely related to softening of loquat fruit during the postharvest period.     

Effect of wounding on cell wall hydrolase activity in tomato fruit

Changes in the activity of the cell wall hydrolases – polygalacturonase (EC 3.2.1.15), pectinesterase (EC 3.2.1.11) and β-galactosidase (EC 3.2.1.23) – have been investigated following wounding of tomato fruit pericarp tissue (Lycopersicon esculentum cv. Ailsa Craig). In ripening fruit wounding appears to arrest the further synthesis of polygalacturonase. β-Galactosidase synthesis may also have been arrested in ripening fruit. The level of pectinesterase declined over the first 24 h following harvest, and since this was apparent in both wounded and unwounded tissue may be related to a harvest, rather than a wounding effect. There was a recovery of activity in intact fruit by 48 h after harvest but this seems to be impaired in wounded tissue. In the case of pectinesterase, this observation was extended to examine the changes in isoform profile and it appeared that the decline of this enzyme may be associated with the reduction of one specific isoform — PE2. In contrast to ripening fruit, wounding of fruit at the fully ripe stage appears to have no significant effects on the activities of any of these three enzymes.     

Influence of aqueous 1-methylcyclopropene concentration, immersion duration, and solution longevity on the postharvest ripening of breaker-turning tomato (Solanum lycopersicum L.) fruit

The influence of aqueous 1-methylcyclopropene (1-MCP) concentration, immersion duration, and solution longevity on the ripening of early ripening-stage tomato (Solanum lycopersicum L.) has been investigated. Tomato fruit at the breaker-turning stage were fully immersed in aqueous 1-MCP at 50, 200, 400 and 600 μg L⁻¹ for 1 min, quickly dried, and then stored at 20 °C. Ethylene production, respiration, surface color development, and rate of accumulation of lycopene and polygalacturonase (PG) activity were suppressed and/or delayed in fruit exposed to aqueous 1-MCP. Suppression of ripening was concentration dependent, with maximum inhibition in response to 1 min immersion occurring at concentrations of 400 and 600 μg L⁻¹. Climacteric ethylene peaks were delayed approximately 6, 7, and 9 d and respiration was strongly suppressed in fruit treated with aqueous 1-MCP at 200, 400, and 600 μg L⁻¹, respectively, compared with control fruit. Fruit firmness, lycopene content, PG activity, and surface hue of fruit treated at the three higher levels remained strongly suppressed compared with control. Skin hue values and pericarp lycopene content in response to treatment at the subthreshold 50 μg L⁻¹ provided evidence for differential ripening suppression in external versus internal tissues. Maximum delay of softening and surface color development in response to 50 μg L⁻¹ aqueous 1-MCP occurred following immersion periods of between 6 and 12 min. Factors affecting fruit penetration by aqueous 1-MCP and mechanisms contributing to recovery from 1-MCP-induced ripening inhibition are discussed.     

A high temperature/low oxygen pulse improves cold storage disinfestation

Short periods of elevated temperature under controlled atmospheres (CA) effectively control insect pests. Cold treatment is also an effective non-chemical disinfestation process. If synergistic effects can be found by combining treatments, these may provide opportunities for cost reduction. Tests were performed to evaluate the tolerance of Packham's Triumph pears (Pyrus communis L.) to a range of temperatures (30–40 °C) combined with low oxygen (O₂ < 1 kPa). Treatment duration was 16–48 h and was followed by 1 month storage at 0 °C under air. When held at 30 °C, pears withstood up to 30 h of hypoxia. After cold storage, pears ripened slightly faster than controls but were undamaged. A temperature of 35 °C induced slight skin browning, and 40 °C resulted in substantial skin blackening. Some treatments were also tested on survival of lightbrown apple moth (LBAM), Epiphyas postvittana (Walker). All developmental stages were subjected to either 16 h at 30 °C, or 16 h under hypoxia, or 1 month at 0 °C, or a combination of the three treatments. With all treatments combined, all eggs, larvae and adults were killed. Only 4% of the pupae produced adults and combined treatments led to an increase in pupa mortality of 38%. A combined treatment (tolerated by pears) consisting of 30 h at 30 °C under low O₂ plus 1 month cold storage under air, killed 100% of LBAM pupae, and 100% of 5th instar larvae of both codling moth, Cydia pomonella (L.), and oriental fruit moth, Grapholita molesta (Busck). Implementation of such treatments would not require substantial investments for fruit industries equipped with CA storage facilities.     

Chilling-induced oxidative stress and antioxidant responses in mume (Prunus mume) fruit during low temperature storage

Mume (Prunus mume Sieb. et Zucc.) fruit are harvested and consumed at the mature green stage and have a short storage life at ambient temperature. While cold temperature extends their storage life, improper refrigeration causes severe chilling injury (CI), with fruit suffering more severe CI at of 5–6 °C than at 1 °C. The objective of this research was to determine the involvement of reactive oxygen species (ROS) and antioxidant systems in fruit under chilling stress. ‘Nankou’ fruit were stored at 1 °C or 6 °C for 15 days. Hydrogen peroxide, a preventive ROS, decreased at a slower rate at 6 °C than 1 °C during storage. Malondialdehyde (MDA), an indicator of lipid peroxidation caused by ROS, increased during storage and the contents were higher in fruit stored at 6 °C than at 1 °C. On the other hand, fruit stored at 6 °C had a lower total antioxidant capacity (TAC) and lower activities of antioxidant-related enzymes including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) than at 1 °C. These results indicate that the fruit at 6 °C had more oxidative stress; thus the fruit had more severe CI symptoms than at 1 °C.     

Effect of high-pressure hot-water washing treatment on fruit quality, insects, and disease in apples and pears: Part I. System description and the effect on fruit quality of ‘d’Anjou’ pears

A manually operated high-pressure hot-water washing system consisting of a boiler, hot-water mixing tank, contact loop, heat exchanger, spray mixing tank, high-pressure hot-water washing manifold, low-pressure fresh water rinse manifold, and pressure pump was constructed and installed in a packingline. The system developed 20–50 °C washing water at pressures up to 980 kPa. ‘d’Anjou’ pears (Pyrus communis L.), shortly after harvest, and after storage for 3 and 4 months in regular air (RA) or for 4, 7 and 8 months in controlled atmosphere (CA) at −1 °C were washed through the packingline with different wetting agents (0.1% Silwet, 0.01 and 0.1% Defoamer, and water), water pressures (regular and high-pressure (210–980 kPa)), water temperatures (control (tap water, 4–22 °C), 40 °C, and 50 °C), and brushes (soft and firm), respectively. The effect of the washing conditions on fruit quality was investigated after 1 month of storage at −1 °C to simulate shipping condition, and then again after 1 week at 20 °C to simulate marketing condition. Hot-water caused severe heat scald. When nozzle temperature was 50 °C, the incidence of heat scald increased to over 50% for the fruit stored in RA for 3 months. Combined with hot-water, 540 kPa high-pressure washing increased the incidence of friction discoloration. There were lower incidences of friction discoloration and heat scald for fruit stored in CA for 7 months, in comparison to that in RA for 3 months. However, those fruit did not ripen properly as indicated by a high extractable juice content. Fruit washed at harvest had minor incidences of friction discoloration regardless of different brushes, water pressures, and wetting agents. Fruit washed after storages in either 4 months RA or 4 or 8 months CA suffered a high incidence of friction discoloration including scuffing symptoms and pressure marking. The firm brushes caused a higher incidence of friction discoloration mainly because of scuffing symptoms. However, no differences were found between different water pressures and wetting agents with respect to friction discoloration. Fruit stored for 4 months RA suffered 26–28% friction discoloration in comparison to 16–18% in CA stored fruit with firm brush washing. Extended CA storage increased friction discoloration even with soft brush washing. The results suggest that a washing system with high-pressure spray, <30 °C warm water, wetting agent Defoamer and rotating soft brushes were significantly effective in removing surface pests and decay control without causing internal or external damage of fruit.     

Effect of high-pressure hot water washing treatment on fruit quality, insects, and disease in apples and pears: Part II. Effect on postharvest decay of d’Anjou pear fruit

A hot water pressure process (HWP) was evaluated for its effect on conidia of Penicillium expansum and on development of blue mold, gray mold, and mucor rot of d’Anjou pear fruit. Spores were removed from the water system through dilution and also as a result of hot water in the system that was lethal to the spores. When the system was heated, viable spores were not detected after 2–4 h of operation. Reductions in decay in the HWP system were 36, 29, and 13% for Botrytis cinerea, Mucor piriformis, and P. expansum, respectively. The response of P. expansum appeared related to the length of time fruit was in cold storage. Heat injury was observed on fruit treated with 40 and 50 °C water but not on fruit at 30 °C nozzle temperature. The HWP system described in this study should be considered as a component of an integrated decay control strategy.     

The effect of delays in establishment of a static or dynamic controlled atmosphere on the quality of ‘Hass’ avocado fruit

The effect of delays of 1, 5, 10 or 15 d after harvest in establishing a static controlled atmosphere (SCA) or dynamic controlled atmosphere (DCA) on the quality of ‘Hass’ avocados (Persea americana Mill.) was investigated. Fruit were stored at 5 °C in SCA (5% O₂/5% CO₂) or DCA (<3% O₂/0.5% CO₂) for 6 weeks and compared with fruit stored in air. In addition, to determine whether increasing the CO₂ in the DCA would affect the fruit quality, DCA-stored fruit were compared with fruit held in a DCA with 5% CO₂ (DCA + CO₂) established 1 d after harvest. The quality of fruit was assessed at the end of storage and after ripening at 20 °C. DCA-stored fruit ripened in 4.6 d compared with 7.2 d for SCA-stored fruit, or 4.8 d for air-stored fruit. In addition, the incidences of stem end rot (SER), body rot (BR) and vascular browning (VB) were lower in DCA-stored fruit (35%, 29% and 29%, respectively) than in SCA-stored fruit (57%, 52% and 49%, respectively), or air-stored fruit (76%, 88% and 95%, respectively). Delaying the establishment of both SCA and DCA for 15 d resulted in significantly more advanced skin colour at the end of storage (average rating score 11.9) compared with other delay periods (4.6–5.1). There was no significant effect of delay on the time to ripen, skin colour when ripe or any ripe fruit disorder incidence. The incidence of diffuse flesh discolouration (DFD) was not only <1% when averaged over all delays but only occurred at >0.5% incidence in the 15 d delay treatment in DCA (4.8%) and not in SCA. The incidence of diffuse flesh discolouration was 62% in air-stored fruit. Inclusion of 5% CO₂ in DCA retarded fruit ripening from 4.7 to 6.9 d and increased the incidence of rots at the end of storage from 5% to 14%, and increased the incidence in ripe fruit of SER from 30% to 56% and of BR from 27% to 55%. It is concluded that fruit quality was better after CA storage than after air storage, and that DCA storage was better than SCA. The effect of DCA is to independently reduce the time to ripen after storage and the incidence of rots when ripe. Delaying the application of SCA or DCA did not affect the expression of rots, but may increase the incidence of DFD. Inclusion of CO₂ at 5% in CA retarded fruit ripening but stimulated rot expression and should not be used for CA storage of New Zealand grown ‘Hass’ avocados.     

Plant oil emulsion modifies internal atmosphere, delays fruit ripening, and inhibits internal browning in Chinese pears

'Laiyang Chili’ and ‘Ya Li’ (Pyrus bertschneideri Reld) pears were treated with 3, 6, and 9% emulsions of commercial or refined (reduced -tocopherol levels) plant (soybean, corn, peanut, linseed, and cottonseed) oils at harvest an stored at 0°C for 6 months. Effects of oil treatments on ethylene production, respiration, fruit firmness, fruit color, soluble solid content (SSC), titratable acids (TA), internal browning (IB), and internal CO₂, O₂, and ethanol were studied. At the same concentration, oil treatments induced similar responses regardless of their sources or their -tocopherol concentrations. In both cultivars, ethylene production and respiration in fruit treated with 9% oils were lower in early storage and higher in late storage than that in the controls. Oils at 6% reduced IB, at 9% inhibited IB completely, and at 3% was not effective after 6 months at 0°C and 7 days at 20°C. Plant oil treatment maintained fruit color, firmness, SSC, and TA in a concentration-dependent manner during storage. In the first 4 months storage, 9% corn oil-treated fruit contained similar partial pressure of CO₂ and O₂ as the controls. After 5 months storage, oil-treated fruit contained higher partial pressure of CO₂ and lower levels of O₂ than the controls. When held at 20°C for 7 days, changes of internal CO₂ and O₂ were slower but partial pressure of CO₂ were higher, and O₂ were lower, in 9% corn oil-treated fruit than in the controls. Internal ethanol was not affected by oil treatment compared with control, either during storage or 7 days at 20°C. No off-flavor was detected in either oil-treated and control fruit by sensory evaluation.     

Effect of combined application of heat treatments and plastic packaging on keeping quality of ‘Oroblanco’ fruit (Citrus grandis L.×C. paradisi Macf.)

Combinations of various heat treatments with individual fruit sealing, packaging in polyethylene liners or waxing were tested as means to control pathological and physiological spoilage of ‘Oroblanco’ fruit (Citrus grandis L.×C. paradisi Macf.). The following heat treatments were used: curing at 36°C for 72 h, hot water dip at 52°C for 2 min or ‘hot drench brushing’ at 52, 56 or 60°C for 10 s. The standard packinghouse treatment included waxing with addition of thiabendazole (TBZ) and 2,4- isopropyl ester. The fruit was stored for 2 weeks at 1°C (simulated low-temperature quarantine treatment), followed by 12–13 weeks at 11°C (simulated sea transportation to Japan) and 1 additional week at 20°C (simulated retail shelf-life period). The lowest weight loss and the highest firmness were observed with individually sealed fruit. Polyethylene liners were usually more efficient for weight loss control than waxing. However, the liner packaging enhanced the risk of postharvest disease development, if not accompanied by appropriate decay-controlling measures. Applying TBZ, hot water dip or curing controlled the development of postharvest pathogens, especially that of Penicillium molds. In another trial, both hot drench brushing at 56 or 60°C and hot water dip reduced decay incidence. Hot drench brushing at 60°C and hot water dip slowed fruit softening and reduced buttons abscission. In addition, the hot drench brushing at 60°C significantly delayed the loss of ‘Oroblanco’ green rind color, especially at the stylar and stem ends of the fruit. The hot dip at 52°C inhibited yellowing only when combined with individual seal-packaging.     

Spear yield and quality of white asparagus as affected by soil temperature

In three consecutive years two asparagus cultivars (Gijnlim, Grolim) were cultivated at three different temperatures in the ridge surface ranging from 12 to 26 °C to assess (1) the onset of spear yield, (2) the mean daily yield increase per plant, and (3) the establishment of spear quality defects. The objective was to determine the temperature dependence of the spear growth and quality of white asparagus with respect to different cultivars and the harvest year.

The mean time interval Δt from the beginning of the temperature treatment to harvest start was 16.5 d at the reference temperature of 20 °C. This time interval corresponded to a thermal time of 255 °C d at a base temperature of 4.4 °C. The mean yield increase per plant at the reference temperature was 17.4 g d⁻¹. The temperature dependence of Δt and was expressed by the relative change of these quantities per 1 °C alteration, which were on average 0.08 and 0.14 °C⁻¹, respectively. The frequency of quality defects (rusted spears, split spears, hollow/club-shaped spears, spears with open heads) and grade I quality depended significantly (P < 0.05) on the temperature, cultivar, and harvest year. Generally, ‘Gijnlim’ showed fewer quality defects than ‘Grolim’, whereas spears without defects were most frequent for those grown between 18 and 22 °C. With rising temperatures, the frequency of split or hollow/club-shaped spears and spears with open heads increased, while the frequency of rusted spears decreased. The derived functions of yield and quality parameters should improve the controlling of the yield and quality of white asparagus spears at varying temperatures in the ridge.     

Combined effects of 1-methylcyclopropene, calcium chloride dip, and/or atmospheric modification on quality changes in fresh-cut strawberries

The aim of this study was to determine the effects of 1-methylcyclopropene, 1-MCP (1 μL L⁻¹ for 24 h at 5 °C) on quality attributes and shelf life of fresh-cut strawberries. The 1-MCP was applied before (whole product) and/or after cutting (wedges), followed by storage in a continuous flow of air or air +1 μL L⁻¹ C₂H₄. The combined effects of 1-MCP and CaCl₂ dips (1% for 2 min) and/or CA (3 kPa O₂ + 10 kPa CO₂) were also examined. The application of only 1-MCP before and/or after cutting did not have a significant effect on firmness and appearance quality during storage for up to 12 days at 5 °C. The exposure to a continuous flow of 1 μL L⁻¹ C₂H₄ in air during storage did not increase the softening rate. 1-MCP applied before cutting or both before and after cutting of the strawberries increased respiration rates but reduced C₂H₄ production rates. Exposure to 1-MCP had a synergistic effect when combined with CaCl₂ plus CA. The combined treatment of 1-MCP + CaCl₂ + CA slowed down softening, deterioration rates, TA and microbial growth. Compared to the control, which had a 6-day shelf life, the shelf life of fresh-cut strawberries subjected to the combination treatment was extended to 9 days at 5 °C.     

The components of lucerne (Medicago sativa) leaf area index respond to temperature and photoperiod in a temperate environment

Irrigated crops of ‘Grasslands Kaituna’ lucerne were grown for 5 years in a temperate climate at Lincoln University, Canterbury, New Zealand (43°38′S, 172°28′E). From these the response of the components of leaf area index (LAI) to environmental factors was determined. A broken stick temperature threshold with a base temperature (T_b) of 1 °C at air temperatures (T_a) <15 °C and a T_b = 5 °C for T_a ≥ 15 was required to accumulate thermal time (Tt). Using this, the appearance of nodes on the main-stem (phyllochron) was constant in Tt within a re-growth cycle (30–42 days). The phyllochron was 37 ± 7 °Cd but declined from 60 to 37 °Cd as photoperiod decreased from 15.7 to 11.4 h. Branching began at the appearance of the fifth main-stem node with 2.5 secondary nodes produced per main-stem node in spring re-growth cycles but only 1.7 produced in summer. Leaf senescence increased from 0.3 to 1.08 leaves per main-stem node after the appearance of the ninth node. Spring re-growth cycles had a mean individual leaf area of 170 mm² compared with 400 mm² for summer re-growth cycles. These results demonstrate systematic variation in LAI components and suggest they need to be considered separately in response to environmental factors to provide a quantitative framework for crop simulation analyses of lucerne canopy development.     

Effect of high temperature stress on ethylene biosynthesis, respiration and ripening of ‘Hayward’ kiwifruit

Temperatures up to 35°C have been shown to increase ethylene production and ripening of propylene-treated kiwifruit (Stavroulakis, G., Sfakiotakis, E.M., 1993. We attempted to study the regulation by high stress temperature of the propylene induced ethylene biosynthesis and ripening in ‘Hayward’ kiwifruit. ‘Hayward’ kiwifruit were treated with 130 μl/l propylene at temperatures from 30 to 45°C up to 120 h. Ethylene biosynthesis pathway and fruit ripening were investigated. Propylene induced normal ripening of kiwifruit at 30–34°C. Fruit failed to ripe normally at 38°C and above 40°C ripening was inhibited. Propylene induced autocatalytic ethylene production after a lag period of 24 h at 30–34°C. Ethylene production was drastically reduced at 38°C and almost nil at 40°C. The 1-aminocyclopropane-1-carboxylic acid (ACC) content was similar at 30–38°C and was very low at 40°C. The 1-aminocyclopropane-1-carboxylate synthase (ACC synthase) and 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase) activities decreased with a temperature increase above 30°C, but ACC oxidase decreased at a faster rate than ACC synthase. Fruit not treated with propylene showed no ripening response or ethylene production. However, kiwifruit respiration rate increased with temperature up to 45°C, reaching the respiration peak in 10 h. At temperatures up to 38°C, propylene treatment enhanced the respiration rate. After 48 h at 45°C, fruit showed injury symptoms and a larger decrease in CO₂. The results suggest that high temperature stress inhibits ripening by inhibiting ethylene production and sensitivity while respiration proceeds until the breakdown of tissues.     

Mortality of eggs and third instar larvae of Anastrepha ludens and A. obliqua with insecticidal controlled atmospheres at high temperatures

The in vitro mortality of eggs and third instar larvae of Anastrepha ludens and A. obliqua was determined after exposure to 21 treatments of air or controlled atmospheres (CA) at high temperatures and 50% RH. Air at 44°C for 160 min caused very low mortality, which increased significantly by CA. Higher temperatures caused a more rapid kill. One hundred percent mortality was achieved for third instar larvae of both species in air or CA at 48°C for 220 min. A 100% mortality of eggs of A. ludens was achieved in air at 51°C for 240 min or in CA at 52°C for 240 min, and 100% mortality of eggs of A. obliqua was achieved in air or in CA at 55°C for 240 min. A. obliqua was slightly more tolerant than A. ludens, and eggs were more tolerant than third instar larvae in both species. CA had a synergistic effect at <50°C, but was slightly less effective than air at higher temperatures. Low O₂ concentrations were more effective than high CO₂ levels. The mean estimated temperatures for 50, 99 and 99.9968% mortality (LT₅₀s, LT₉₉s, LT_99.9968s) of eggs of A. obliqua (the most tolerant) exposed to 0 kPa O₂+50 kPa CO₂ for 240 min were 49.4, 54.8 and 60.9°C, respectively. We conclude that dry hot air at ≥44°C and 50% RH in CA (0 kPa O₂+50 kPa CO₂), for 160 min or longer, is effective in increasing mortality of eggs and third instar larvae of A. ludens and A. obliqua.     

Response of some Andean cultivars of quinoa (Chenopodium quinoa Willd.) to temperature: Effects on germination, phenology, growth and freezing

This article presents various experiments conducted under semi-controlled conditions to determine the effects of temperature on germination, phenology, growth and freezing in Chenopodium quinoa, a pseudocereal originating from the cold and dry Andean altiplano. Traditional landraces and recently released cultivars from distinct geographical origins were compared in order to look for local adaptation or breeding improvement with respect to low temperatures. Germination was evaluated in 10 cultivars at temperatures between 2 and 20 °C. Plant growth and development were examined in three cultivars over the growing cycle, under minimum temperature between 8 and 13 °C and maximum temperature between 20 and 28 °C. The thermal time concept was used to compare the various treatments and estimate the phyllochron, as well as the base temperature and optimum temperature for leaf appearance, time to flowering and leaf width growth. Two cultivars at the vegetative stage were compared for night freezing tolerance down to −6 °C, registering leaf exotherms and plant survival rate. The influence of plant water status and the possible protective or detrimental role of leaf epidermal vesicles were also examined. Low temperatures down to 2 °C delayed germination without impeding it totally. Base temperature for germination varied between −1.9 and +0.2 °C, with negative values in 9 cultivars out of 10. Thermal sensitivity in germination was not related to the geographic origin of the cultivars. Leaf appearance and time to flowering showed similar base temperatures near 1 °C. Phyllochron varied from 12.9 to 17.2 °C d with lower values in the two recently released varieties than in the traditional landrace. Leaf width increased from a base temperature around 6 °C up to an optimum temperature between 20 and 22.5 °C. Freezing experiments showed that no plant could survive after 4 h at −6 °C, while no serious effect was noted down to −3 °C. Leaf exotherms confirmed that ice nucleation occurred between −5 and −6 °C in most of the plants, the traditional landrace showing a lower freezing tolerance than the selected line. Low leaf water status delayed the freezing process, while leaf vesicles did not seem to play any protective or detrimental role towards leaf freezing. Implications of these results for quinoa crop adaptation to the Andean environment are discussed.     

Effect of fruit maturity on efficiency of 1-methylcyclopropene to delay the ripening of bananas

Three bunches of unripe ‘Williams’ banana fruit of different maturity, 173, 156 and 71 days from bunch emergence, were harvested. Fruit from the top, bottom and middle hands from each bunch were fumigated for 24 h with 1-methylcyclopropene (1-MCP) at 0, 5, 50 or 500 nl l⁻¹ at 20^oC. All fruit were then stored at 20^oC in air containing 0.1 μl l⁻¹ ethylene and the time taken for each fruit to ripen (green life) was noted. The green life of fruit treated with 500 nl l⁻¹ 1-MCP varied with fruit maturity. In the two most mature bunches it was 27.9±2.3 days, 4-fold longer than fruit fumigated with 0 nl l⁻¹ 1-MCP (6.7±0.6 days). In the least mature bunch, green life was 39.7±3.0 days, 1.5-fold longer than fruit fumigated with 0 nl l⁻¹ 1-MCP (25.7±2.5 days). Most fruit treated with 500 nl l⁻¹ 1-MCP showed an unacceptable uneven skin colouration when ripe. There was no significant effect on green life of 1-MCP at 50 nl l⁻¹ and 5 nl l⁻¹. Other fruit from these bunches were not exposed to 1-MCP and were held in ethylene-free air until ripe. In the two most mature bunches, these fruit had a significantly shorter green life (11.2±5.6 days in hand 1; 18.9±4.1 days in hands 4 and 6) than fruit that were fumigated with 500 nl l⁻¹ 1-MCP. In the least mature bunch, however, these fruit had a significantly longer green life (56.0±5.9 days) than 1-MCP treated fruit. Since the effectiveness of 1-MCP varied with fruit maturity and in any commercial consignment there is a mixture of fruit maturity, it is concluded that 1-MCP has limited commercial potential for the storage of unripe ‘Williams’ bananas.     

Phospholipase A2 and postharvest peel pitting in citrus fruit

The role of phospholipase A₂ (PLA₂) activity in development of postharvest peel pitting in mature ‘Fallglo’ tangerines [Bower citrus hybrid (Citrus reticulata Blanco × C. reticulata Blanco × C. paradisi Macf.) × Temple (C. reticulata Blanco × Citrus sinensis L.)] and ‘Navel’ oranges (Citrus sinensis L. Osbeck) was investigated. Changes in RH from 30% to 90% followed by fruit waxing increased electrolyte leakage and PLA₂ activity in flavedo, and induced pitting. Treatment with an aqueous dip of aristolochic acid (AT), a specific inhibitor of secretory phospholipase A₂ (sPLA₂) activity, immediately before transfer from 30% to 90% RH storage, markedly reduced peel pitting symptoms. Five genes encoding various phospholipase As isolated from citrus (three patatin-like and two sPLA₂-like sequences) differentially accumulated in healthy areas, areas with developing lesions and necrotic lesions of disordered fruit. Other PLA₂, phospholipase C, and phospholipase D inhibitors also reduced peel pitting; however, PLA₂ inhibitors were the most effective in preventing the disorder. In addition, phospholipase inhibitors promoted fruit decay, suggesting that innate resistance is impacted by phospholipase action. Together, the results provide evidence for involvement of phospholipase activity in development of postharvest peel pitting symptoms in citrus fruit.     

Storage characteristics and relationships between microbial growth parameters and shelf life of MAP sliced onions

Microbial proliferation and sensory quality aspects of sliced onions were tested at different temperatures (−2, 4 and 10 °C) and atmospheric conditions (with or without 40% CO₂ + 59% N₂ + 1% O₂). The relationships among microorganism growth parameters (the initial cell number (N₀), the maximum cell number (N_max), the maximum specific growth rate (μ_max) and lag-phase (λ)) and the microbial or sensory shelf life were determined. The microorganism growth parameters were obtained by fitting the modified Gompertz equation to the microbial counts. The results showed that color intensity (yellowness), sensory scores and microbial counts increased, and firmness decreased during storage. The total plate counts (TPC) provided the best indication of the spoilage organism growth capacity under tested temperatures and atmospheric conditions. The microbial shelf lives of the tested onions in 40% CO₂ + 59% N₂ + 1% O₂, or at −2, 4 and 10 °C, were 12.5, 9.5, 7, 12, 9 and 6 days, respectively, and their sensory shelf lives were 12, 8, 5, 10.5, 7 and 5 days, respectively. The lag time (λ) of the TPC, coliforms, pseudomonads and yeasts correlated well with the microbial and sensory shelf life results. The correlations between microbial and sensory shelf life, and the μ_max of TPC, lactic acid bacteria (LAB) and coliforms were between (−0.61 and −0.85). The initial microbial counts (N₀) of the five microorganisms showed a slight correlation, and the maximum microbial counts (N_max) of this group showed no obvious correlation with onion shelf life, apart from the LAB and yeasts.     

Effects of the yeast Pichia guilliermondii against Rhizopus nigricans on tomato fruit

The yeast Pichia guilliermondii was examined for its ability to control Rhizopus nigricans on tomato fruit during storage, and in order to highlight the reason for biocontrol, a possible mode of action is discussed. Results showed that autoclaved yeast culture and culture filtrate had no effect on controlling the postharvest disease caused by R. nigricans, although inoculation of P. guilliermondii prior to R. nigricans resulted in enhanced biocontrol efficacy. Moreover, rapid colonization of the yeast on wound sites was observed during the initial 3 days at 20 °C, and then the population stabilized for the remaining 4 days. This phenomenon indicated that at room temperature, P. guilliermondii could acclimatize itself to the environment of tomato fruit wounds and occupy the living space quickly. The results indicate that P. guilliermondii did not produce an antifungal substance, however, competition for nutrients and space on wounds appeared to play a role in the activity of the biocontrol and could be one of the mechanisms. In addition, the fruit inoculated with P. guilliermondii demonstrated changes in peroxidase (POD), polyphenoloxidase (PPO), superoxide dismutase (SOD), catalase (CAT), phenylalanine ammonia-lyase (PAL), chitinase (CHI) and β-1,3-glucanase activities, all of which were correlated with the onset of induced resistance. This result suggests that tomato fruit is capable of responding to the yeast P. guilliermondii, which could activate defensive enzymes and thereby induce host disease resistance.