Effects of post-harvest calcium chloride or salicylic acid treatments on the shelf-life and quality of apricot fruit

Summary

The purpose of this work was to estimate the effects of post-harvest calcium chloride or salicylic acid treatments on the physicochemical characteristics and shelf-life of apricot (Prunus armeniaca L.) ‘Asgar-Abad’ fruit stored at 1ºC in a normal atmosphere for 21 d after harvest. Fruit were dipped in deionised water (control), or in 40, 60, or 80 mM CaCl₂, or in 1.0, 2.0, or 3.0 mM salicylic acid (SA) for 10 min.Total soluble solids (TSS) contents, titratable acidity (TA), ascorbic acid contents, total phenolics contents, and total anti-oxidant activity were determined 7, 14, or 21 d after each treatment. Fresh weight (FW) loss, titratable acidity, and TSS contents were improved by all treatments. Fruit treated with 3 mM SA exhibited the highest phenolics content during the storage period. At the end of the storage period, the highest values of TSS were observed in the 2.0 mM and 3.0 mM SA treatments. This experiment revealed that post-harvest treatment with SA or CaCl₂ prolonged the storage-life and preserved the valuable marketing characteristics of apricot fruit, presumably because of their inhibitory effects on fruit softening, ripening, and senescence. Over 21 d in cold storage, 2.0 mM SA was found to be the best treatment to maintain fruit quality in terms of FW loss, while 60 mM CaCl₂ was optimal for achieving high ascorbic acid concentrations and enhancing the anti-oxidant capacity of fruit.     

Methylene blue increases the tolerance of tomato plants to abiotic stresses

Summary

Environmental stresses such as high temperature and high salinity are known to cause oxidative stress in plants by enhancing the generation of reactive oxygen species (ROS), which have a strong impact on plant development. Mitochondria constitute one of the major sources of ROS in roots. Recently, it has been shown in mammalian systems that methylene blue (MB) at very low concentrations can attenuate mitochondrial ageing by scavenging ROS. In the present study, we tested whether MB could be used to protect tomato (Lycopersicon esculentum L.) seedlings against the harmful effects of high salinity and high root temperature. Tomato seedlings were grown hydroponically and were subjected to two abiotic stresses: high salinity (150 mM NaCl) in the nutrient medium, or high root temperature (35ºC) for 14 d. These stress treatments were applied with or without the addition of 10^–8 M MB. The results showed that, under normal conditions, MB enhanced root and shoot growth, increased root respiration, decreased root H₂O₂ and malonyldialdehyde (MDA) concentrations, and enhanced root superoxide dismutase (SOD) activity. Both high salinity and high root temperature stress impaired root and shoot growth, and caused an enhancement of root oxidative stress. MB had a significant protective effect against both abiotic stresses and restored the levels of oxidative stress-related components (i.e., H₂O₂ and MDA) in root and leaf tissues almost to normal levels. It is hypothesised that MB could confer its protective effect not only through interactions with root mitochondria, but also via additional cellular targets in the root.     

Exogenous CaCl2 reduces salt stress in sour jujube by reducing Na+ and increasing K+, Ca2+, and Mg2+ in different plant organs

In this study, we investigated the effects of 10 mM CaCl₂ on membrane permeability, malondialdehyde (MDA), reactive oxygen species (ROS), and Na⁺, K⁺, Ca²⁺, and Mg²⁺ concentrations in different organs of sour jujube grown under 150 mM NaCl stress. Our results showed 73% leaf wilting in the Na treatment. The Na treatment significantly increased leaf superoxide (O₂^.?) production rates, hydrogen peroxide (H₂O₂) concentrations, cell membrane permeability, MDA concentrations, and Na⁺ concentrations in roots, stems, and leaves. The Na treatment significantly reduced K⁺, Ca²⁺,and Mg²⁺ concentrations in roots, but increased K⁺ concentrations in stems. Compared with the Na treatment, 39% of the leaves showed wilting symptoms in the Na+Ca treatment. The Na+Ca treatment significantly decreased leaf O₂^.? production rates, H₂O₂ concentrations, cell membrane permeability, and MDA concentrations. Moreover, the Na+Ca treatment (1) significantly reduced Na⁺ concentrations in roots, stems, and leaves; (2) significantly increased root K⁺ concentrations; (3) significantly increased K⁺/Na⁺ ratios in roots; (4) significantly increased Ca²⁺ concentrations in stems and leaves, and Mg²⁺ concentrations in roots. In conclusion, exogenous CaCl₂ reduces NaCl stress in sour jujube by reducing Na+ concentrations and increasing K⁺, Ca²⁺, and Mg²⁺ concentrations in various plant organs.     

Nitric oxide alleviates adverse salt-induced effects by improving the photosynthetic performance and increasing the anti-oxidant capacity of eggplant (Solanum melongena L.)

Summary

Nitric oxide (NO) is an active molecule involved in many physiological functions in plants. To characterise the roles of NO in the tolerance of eggplant (Solanum melongena L.) to salt stress, the protective effects of exogenous sodium nitroprusside (SNP), a donor of NO, applied at different concentrations (0, 0.05, 0.1, or 0.2 mM), on plant biomass, photosynthesis, and anti-oxidant capacity were evaluated. The application of SNP alleviated the suppression of growth in eggplant under salt stress, as reflected by a higher accumulation of biomass. In parallel with growth, the application of SNP to salt-stressed plants resulted in enhanced photosynthetic parameters such as the net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (T_r), and intercellular CO₂ concentration (C_i), as well as an increased quantum efficiency of PSII (F_v/F_m), efficiency of excitation capture of open PSII centres (F_v’/F_m’), quantum yield of PSII ( _psii) and photochemical quenching coefficient (qP). Furthermore, exogenous SNP also reduced significantly the rate of production of O₂^{? –} radicals and the concentrations of malondialdehyde (MDA) and H₂O₂. It also increased the activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in eggplant leaves grown under salt stress. The results indicated that the protective effects of NO against salt stress in eggplant seedlings were most likely mediated through improvements in photosynthetic performance and the stimulation of anti-oxidant capacity.     

Abscisic acid alleviates the deleterious effects of cold stress on ‘Sultana’ grapevine (Vitis vinifera L.) plants by improving the anti-oxidant activity and photosynthetic capacity of leaves

The effects of exogenous application of abscisic acid (ABA) on anti-oxidant enzyme activities and photosynthetic capacity in ‘Sultana’ grapevine (Vitis vinifera L.) were investigated under cold stress. When vines had an average of 15 leaves, 0 (control), 50, 100, or 200 µM ABA was sprayed to run-off on all leaves of each plant. Twenty-four hours after foliar spraying with ABA, half (n = 5) of the water-only control vines and half (n = 5) of each group of ABA-treated plants were subjected to 4°C for 12 h, followed by a recovery period of 3 d under greenhouse conditions (25°/18°C day/night). The remaining plants in each treatment group were kept at 24°C. Cold stress increased H₂O₂ and malondialdehyde (MDA) concentrations in vine leaves, whereas all foliar ABA treatments significantly reduced their levels. Chilled plants showed marked increases in their total soluble protein contents in response to each ABA treatment. ABA significantly increased the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in cold-stressed grapevine leaves. In contrast, cold stress markedly decreased the rates of leaf photosynthesis (A) and evaporation (E), stomatal conductance (g_s), and chlorophyll concentrations in leaves, but increased intercellular CO₂ concentrations (C_i) in leaves. Treatment with all concentrations of ABA resulted in lower leaf A, E, and g_s values, but higher C_i values at 24°C. However, following cold stress, ABA-treated vines showed higher leaf A, E, and g_s values, but lower C_i values compared to control vines without ABA treatment. The application of 50–200 µM ABA allowed chilled vines to recover more quickly when re-exposed to normal temperatures, enabling the vines to resume their photosynthetic capacity more efficiently following cold stress. These results showed that, by stimulating anti-oxidant enzyme systems and alleviating cold-induced stomatal limitations, ABA reduced the inhibitory effect of cold stress on the rate of CO₂ fixation in ‘Sultana’ grapevine plants.     

Effect of electrical conductivity,fruit pruning,and truss position on quality in greenhouse tomato fruit

Summary

The combined effects of electrical conductivity (an EC of 2.5 dS m^–1 or 8 dS m^–1 in the root zone) and fruit pruning (three or six fruit per truss) on tomato fruit quality were studied in a greenhouse experiment, planted in January 2005. Taste-related attributes [dry matter content (DM), total soluble solids content (SSC), titratable acidity (TA), glucose, fructose and citric acid content] and health-promoting attributes (lycopene, βcarotene, vitamin C, and total anti-oxidant activity) of tomato fruits harvested on the vine from the fifth or tenth truss positions were determined. The quality of tomato fruits was improved by high EC. A high EC in the root zone increased the DM content, total SSC, TA, as well as glucose, fructose and citric acid contents. A significantly higher lycopene and βcarotene content was also observed [on a fresh weight (FW) and dry weight (DW) basis] with a high EC in the root zone. The accumulation of different compounds that determine tomato fruit quality differed between the fifth and tenth truss. In particular, the lycopene content was reduced, whereas the βcarotene content was increased in the tenth truss with respect to the fifth truss, most likely because of higher temperatures during ripening of the tenth truss. Fruit pruning increased fruit FW by 42% and positively influenced the DM content and total anti-oxidant activity, while a negative effect was observed on lycopene and citric acid contents (on a FW and DW basis). EC and fruit pruning both had a strong effect on fruit size; however, EC had a much stronger impact on taste and health-related fruit quality attributes. A small interaction between EC and fruit pruning was found for marketable yield, fructose and glucose content, fruit firmness, and P and Ca concentrations in fruits.     

Response of kiwifruit (Actinidia deliciosa cv. Allison) to post-harvest treatment with 1-methylcyclopropene

Summary

Experiments were conducted to observe the effect of different concentrations of 1-methylcyclopropene (1-MCP) on the post-harvest life and quality of ‘Allison’ kiwifruit (Actinidia deliciosa). Fruit were treated with 1-MCP at 0.5 µl l^–1, 1.0 µl l^–1, or 2.0 µl l^–1, un-treated fruit served as controls. Each 1-MCP treatment was applied for 24 h at 20°C. After treatment, fruit were transferred to ambient temperature storage (22º ± 4ºC; 65 – 70% relative humidity) for 18 d, during which time observations on various physical, physiological, and biochemical parameters were recorded at 3 d intervals. Our results indicated that 2.0 µl l^–1 1-MCP was the most effective treatment to delay softening and ripening in ‘Allison’ kiwifruit, as such fruit showed the lowest mean weight loss (9.8 ± 0.2%), the highest mean fruit firmness value (32.7 ± 0.2 N), and began to ripen only after 12 d in storage, whereas untreated fruit started ripening on day-6 of storage. The activities of fruit softening enzymes such as polygalacturonase (PG; 58.5 ± 0.3 µg galacturonic acid g^–1 FW h^–1), and lipoxygenase (LOX; 3.96 ± 1.3 µmoles linoleic acid oxidised min^–1 g^–1 FW h^–1) were lower, and total phenolics (TP) contents (24.3 ± 0.3 mg 100 g^–1) and anti-oxidant (AOX) activities (12.5 ± 0.03 µmol Trolox g^–1 FW h^–1) were higher in 1-MCP-treated fruit than in untreated fruit (PG, 98.3 ± 0.5 µg galacturonic acid g^–1 FW h^–1; LOX, 4.39 ± 1.0 µmoles min^–1 g^–1 FW h^–1; TP, 5.3 ± 0.6 mg 100 g^–1; AOX, 4.7 ± 0.02 µmol Trolox g^–1 FW h^–1, respectively). In addition, 1-MCP-treated fruit exhibited lower rates of respiration (48.3 ± 0.4 ml CO₂ kg^–1 h^–1) and ethylene production (30.2 ± 0.02 µl kg^–1 FW h^–1) than untreated fruit (58.9 ± 0.6 ml CO₂ kg^–1 h^–1; 38.7 ± 0.04 µl kg^–1 FW h^–1, respectively). Similarly, 1-MCP-treated fruit had higher titratable acidity (TA; 1.33 ± 0.3%) and ascorbic acid (AA) contents (115.9 ± 2.6 mg 100 g^–1 pulp) and lower soluble solids contents (SSC; 8.33º ± 0.2º Brix) than untreated kiwifruit (TA, 1.0 ± 0.2 %; AA, 105.3 ± 2.2 mg 100 g^–1 pulp; SSC, 13.7º ± 0.3º Brix, respectively). Thus, 2.0 µl l^–1 1-MCP can be used for the post-harvest treatment of ‘Allison’ kiwifruit to enhance its shelf-life and marketability by approx. 6 d.     

Effect of methyl jasmonate on reactive oxygen species,antioxidant systems,and microstructure of Chinese winter jujube at two major ripening stages during shelf life

The effect of post-harvest application of methyl jasmonate (MeJ) on reactive oxygen species, antioxidant systems, and cellular structure in Chinese winter jujube (Ziziphus Jujuba Mill.) at the major ripening stages of green maturity (GM) and half-red maturity (HM) were investigated. Jujube fruit at each ripening stage were treated with 0, 50, 100, and 200?μmol?l^?1 MeJ for 24 h, then stored at 20 ± 2°C for shelf-life testing. Thereafter, changes in firmness, color, respiration rate, superoxide anion (O₂^?), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), ascorbic acid (AsA), and glutathione (GSH) were measured at 4-d intervals for up to 8 d. Results showed that, in comparison with control fruit, MeJ treatment effectively suppressed the decrease of firmness, color, and respiration rate, inhibited the production of O₂^? and accumulation of H₂O₂ and MDA, maintained higher activities of SOD and CAT and contents of AsA and GSH, and preserved the integrity of cell membranes and organelles. The degree of maturity influenced the benefits of MeJ application. The 100?μmol?l^?1 MeJ treatment had a positive impact on antioxidant systems for GM fruit, whereas a MeJ concentration below 100 μmol l^?1 was found to extend the shelf life of HM fruit.     

Anti-oxidant enzyme responses during in vitro embryogenesis in Catharanthus roseus

Summary

The present study was carried out to analyse the activities of several anti-oxidant enzymes at various stages of somatic embryogenesis in Catharanthus roseus. The hypothesis was that anti-oxidant enzymes accumulated as part of a cellular defence mechanism in response to stress. We therefore measured superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities in various in vitro-grown tissues such as embryogenic and non-embryogenic calli, and in embryos at various stages. SOD activity increased gradually from the early embryogenic stage to heart-shaped stage embryos, but declined in the later stages (i.e., torpedo-shaped and cotyledonary embryos). In contrast, APX activity was high in non-embryogenic callus and decreased rapidly during the stage of embryo initiation. This pattern was the same for CAT. The maximum CAT activity was observed in non-embryogenic callus, then it declined almost linearly at the embryonic and post-embryonic developmental stages. The effect of exogenous hydrogen peroxide (H₂O₂) on in vitro embryogenesis was also evaluated. Lower H₂O₂ levels (0.025 mM) promoted embryo formation, whereas higher levels (0.10 mM) inhibited embryogenesis in C. roseus. Finally, higher soluble protein, free amino acid, and proline contents were found in embryogenic calli compared to non-embryogenic calli.     

Effects of post-harvest salicylic acid treatment on fruit quality and anti-oxidant metabolism in pineapple during cold storage

Summary

Pineapple (Ananas comosus L. ‘Comte de Paris’) fruit at commercial maturity (180 fruit per treatment, three replicates) were immersed in 0, 1.0, 3.0, or 5.0 mM salicylic acid (SA) for 15 min, then stored at 10ºC and 90% relative humidity (RH) for 20 d. After 20 d in cold storage, they were moved to 20ºC for 2 d to simulate shelf-life. Physiological and biochemical responses were studied. The results showed that the 3.0 or 5.0 mM SA treatments lowered the internal browning (IB) index, while the 5.0 mM SA treatment decreased the soluble solids content (SSC), titratable acidity (TA), and soluble sugar content, but increased ascorbic acid (AsA) levels at the end of shelf-life. Furthermore, during cold storage, all SA treatments significantly decreased the rate of tissue respiration in pineapple fruit. SA at 5.0 mM significantly decreased the activities of peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL), but increased the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) compared with the non-SA treated (untreated) controls. Overall, these results indicate that post-harvest treatment with 5.0 mM SA delayed the occurrence of IB in pineapple, extended its shelf-life, and maintained fruit quality during cold storage.     

Effect of low temperatures on pulp browning and endogenous abscisic acid and ethylene concentrations in peach (Prunus persica L.) fruit during post-harvest storage

Summary

Changes in the severity of pulp browning, endogenous abscisic acid (ABA) and ethylene concentrations, and related gene expression in peach (Prunus persica L. ‘Bayuecui’) fruit stored at the biological freezing-point temperature (BFT; 1ºC), at 4ºC, or at room temperature (20ºC; as a control) were investigated.The results showed that fruit stored at room temperature showed climacteric changes in ethylene and ABA concentrations and in levels of expression of the corresponding ethylene synthetase genes (PpACS1, PpACO1) and the gene for a key enzyme of ABA synthesis (PpNCED), concomitant with a significant decrease in fruit firmness and an increase in juice yield. Meanwhile, two sucrose synthase genes (PpSUS1 and PpSUS2) were expressed at relatively low levels. However, fruit firmness decreased slightly and chilling injury (CI) increased significantly 40 d after storage (DAS) at 4ºC, with a significant accumulation of proline [from 8.33 µg g^–1 (at t = 0 d) to 9.125 µg g^–1 (at t = 40 d)]. In contrast, fruit firmness decreased slowly and pulp browning increased slightly 80 DAS at the BFT ( 1ºC), with a lower accumulation of proline than in fruit stored at 4ºC. The concentrations of soluble sugars and titratable acidity decreased during storage at 1ºC, 4ºC, or 20ºC, but there was a peak of soluble sugars at a late stage of storage at the BFT ( 1ºC). The fruit browning index was significantly and positively correlated (R ² = 0.967) with ABA concentration. The decrease in ABA concentration in cold-stored fruit (at both 1ºC and 4ºC) inhibited ethylene production. Moreover, there was no significant correlation between CI in fruit and ethylene production. In conclusion, the decrease in ABA concentration reduced ethylene concentrations and inhibited the development of pulp browning, which resulted in an improved taste, but crisper fruit, when fruit were stored at the BFT (–1ºC).     

Effect of humidity and nutrient feed K/Ca ratio on physiological responses and the accumulation of dry matter,Ca and K in tomato

Summary

Two levels of humidity, high, 0.1 kPa vapour pressure deficit (vpd) and control 0.5 kPa vpd, and four nutrient feed K/Ca mM ratios (4/7, 10/7, 4/2 and 10/2) were applied in all factorial combinations to a nine-week old tomato (Lycopersicon esculentum Mill.) crop for 63 d. The effect on gas exchange, water relations, vegetative growth, yield and accumulation of Ca and K in the shoot was examined. High humidity had a deleterious effect on leaf expansion, delayed truss and fruit maturity and reduced fruit yield. Water uptake was reduced and the Ca concentration of leaf and fruit tissue was increased under high humidity compared with plants grown under control humidity; K accumulation was unaffected. The accumulation of K and Ca in the shoot appeared to be poorly related to the rate of transpiration. The high (10/2 mM) K/Ca ratio nutrient feed had little effect on vegetative growth and yield compared with the low (4/7 mM), but restricted Ca uptake to the fruits at both the high and the control humidity. During the measurement period, 0900–1300 hours, stomatal conductance and leaf water status remained high at elevated humidity, compared with a progressive reduction in leaf water status and low stomatal conductance in the control humidity. A/c_i gas exchange analysis where A is the net CO₂ assimilation rate and c_i is the intercellular partial pressure of CO₂ suggested that, at high humidity, the photosynthetic capacity of the leaves was reduced because of a lower in vivo carboxylation efficiency. However, the mechanism(s) responsible for reduced leaf expansion remains unclear. The complex interrelations between physiological responses, leaf expansion and the uptake and distribution of K and Ca to the shoot, are discussed.     

Effects of exogenous salicylic acid and nitric oxide on lipid peroxidation and antioxidant enzyme activities in leaves of Brassica napus L. under nickel stress

The effects of nickel in combination with salicylic acid (SA) and sodium nitroprusside (SNP), a donor of nitric oxide (NO) on 21-day-old canola plants were evaluated. Exposure to 0.5 mM NiCl₂·6H₂O for 10 days resulted in toxicity symptoms such as chlorosis and necrosis at leaves. Addition of 0.2 mM SA or 0.2 mM SNP slightly reduced the toxic effects of nickel. After application of both SA and NO, these symptoms considerably decreased. Treatment with Ni resulted in a decrease in dry weight of roots and shoots and chlorophyll content of leaves. In Ni-treated plants, level of lipoxygenase activity and malondialdehyde (MDA), H₂O₂ and proline contents significantly increased, while the activities of the antioxidant enzymes such as catalase, guaiacol peroxidase and ascorbate peroxidase decreased in leaves. The results indicated that Ni caused an oxidative stress in canola plants. The Ni-stressed plants exposed to SA or NO, especially to SA + NO, exhibited an improved growth as compared to Ni-treated plants. SA or NO, especially both together considerably reduced root-to-shoot translocation of Ni and increased the activities of the antioxidant enzymes in leaves of Ni-stressed plants. Interaction of SA and NO improved the chlorophyll content and decreased the level of lipid peroxidation, H₂O₂ and proline accumulation in leaves. These results suggest that SA or NO in particular their combination counteract the negative effects of Ni on canola plants.     

Supplementary phosphorus can alleviate boron toxicity in tomato

The effect of supplementary phosphorus on growth and yield of tomato (Lycopersicon esculentum cv. Target F1) plants grown at high boron was investigated. The results showed that high B reduced dry matter, fruit yield and chlorophyll content. High B plus 0.5 or 1 mM P increased plant dry matter, fruit yield and chlorophyll concentrations as compared to high B treatments only. Membrane permeability was not increased significantly due to high B application. In the leaves of plants grown at high boron treatments, superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO) levels were increased. However, supplementary P to nutrient solution containing high B reduced the activities of the earlier mentioned enzymes in leaves but their levels were still higher than those at the control treatments. The study revealed that B status affects the activities of some antioxidant enzymes examined. Boron (B) concentrations increased in leaves and roots in the highest external B treatment as compared to the control treatment. Concentrations of Ca, P and K were significantly lower in the leaves of plants grown at high B than those in the control plants. Supplemented nutrient solution containing high B with 0.5 or 1 mM P increased the tissue concentrations of nutrients. These results indicate that supplementary P can mitigate the adverse effects of high B on fruit yield and growth in tomato plants.     

Slowing the deterioration of mango fruit during cold storage by pre-storage application of oxalic acid

Summary

The effects of pre-storage application of oxalic acid (OA) on the incidence of decay and ripening in mango fruit, and its physiological effects on the peel and flesh of mango were investigated after mango fruit (Mangifera indica L. cv. Zill) were dipped in 5 mM OA for 10 min at 25ºC then stored at 14º ± 1ºC for 5 weeks. In addition, spore germination and mycelium growth of Colletotrichum gloeosporioides Penz. on potato dextrose agar (PDA) media containing different concentrations of OA were measured. Application of OA decreased the incidence of decay and delayed the ripening process in mango fruit during cold storage. However, there was no reduction in fruit quality, as judged by the soluble solids content (SSC) and titratable acidity (TA) of fruit ripened at 25ºC for 3 d, following 3 weeks of cold storage. Oxalic acid-treatment resulted in decreased lipoxygenase (LOX) activity and increased superoxide dismutase (SOD) activity in the peel, and increased ascorbate peroxidase (APX) activity in both the peel and the flesh, coincident with a decrease in reactive oxygen species (ROS).At or above 5 mM, OA with unaltered (natural) pH or after neutralisation, also inhibited C. gloeosporioides development in vitro. It is suggested that the physiological effects of OA, in decreasing LOX activity and enhancing defense against oxidation damage, contributed to delaying the ripening process in mango fruit during cold storage. Thus, pre-storage application of OA could be a promising method to suppress post-harvest deterioration and extend the shelf-life of refrigerated mango fruit, possibly due to a combination of its physiological effect in delaying the ripening process, coupled with an inhibition of the development of pathogens such as C. gloeosporioides.     

Effect of CaCl2 treatment on the acclimatisation of mericlone seedlings of Cattleya and Phalaenopsis

Summary

To increase resistance to environmental stress during the acclimatisation of mericlone seedlings of Cattleya and Phalaenopsis, seedlings were treated with CaCl₂. The effectiveness of CaCl₂ treatment on acclimatisation was determined by investigating the levels of anti-oxidative enzyme activity and reactive oxygen species (ROS), the amounts of chlorophyll and malondialdehyde (MDA), the net rate of photosynthesis (A), and the area of leaf-burn caused by high temperature injury. The activities of four anti-oxidative enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD)] in mericlone seedlings of Cattleya and Phalaenopsis increased with CaCl₂ treatment. The highest increase was in the treatment with 4 mM CaCl₂. Mericlone seedlings treated with 4 mM CaCl₂ had increased SOD, CAT, APX, and POD activities compared with the controls after 35 d of acclimatisation in a greenhouse. The levels of superoxide anions (O₂^?–) and hydrogen peroxide (H₂O₂) were also low. In line with this, any decrease in chlorophyll content, increase in MDA content, drop in A, or injury due to high temperature stress were mitigated by CaCl₂ treatment. These results show that CaCl₂ treatment is effective for the acclimatisation of mericlone seedlings of Cattleya and Phalaenopsis by increasing their resistance to environmental stress.     

Determination of the optimal pre-storage delayed cooling regime to control disorders and maintain quality in ‘Honeycrisp’TM apples

Summary

Several pre-storage time (0, 1, 2, 4, and 6 d) and temperature (3.5º, 10º, 15º, 20º, 25º, and 30ºC) delayed cooling (DC) treatments were tested on harvested ‘Honeycrisp’^TM apples to determine which combination was optimal for reducing soft scald and low temperature breakdown (LTB), while maintaining the highest fruit quality [i.e., firmness, minimal mass loss, titratable acidity (TA), soluble solids content (SSC), absence of rot, and minimal skin greasiness] after 4 months of refrigerated air (RA) storage. Fruit were harvested from three separate Annapolis Valley (Nova Scotia) orchard sites in 2006 and in 2007. Multiple linear regression and surface response curves showed that fruit firmness and SSC generally increased throughout the DC treatment, but were affected curvilinearly by temperature, reaching a maximum at approx. 15ºC, then declining. Loss of fruit mass was positively related to a (day temperature²) interaction, indicating that it increased synergistically the longer and the warmer the DC treatment. Fruit acidity was affected only by temperature, with the highest TA values at approx. 15ºC, then declining at higher DC temperatures. Multiple logistic regression and surface responses demonstrated that the incidence of soft scald declined curvilinearly the longer and the warmer the DC treatment, while LTB declined curvilinearly with increasing DC temperature only. A positive (day² temperature²) interaction indicated that fruit greasiness increased non-linearly as the duration and temperature of DC increased. Collectively, these results show that both soft scald and LTB were suppressed or eliminated by a DC regime of 25ºC for 1 – 2 d, or 30ºC for 1 d, without incurring a major reduction in fruit quality.     

Changes in antioxidants and fruit quality in hot water-treated ‘Hom Thong’ banana fruit during storage

The effects of hot water treatment on antioxidants and fruit quality were investigated in banana fruit of cv. Gros Michel (Musa acuminata, AAA Group, locally called cv. Hom Thong) by immersing fruits in hot water (50 °C) for 10 min, before storage at 25 °C for 10 days or 14 °C for the first 8 days followed by storage at 25 °C for the second 8 days until ripening. Quality parameters including peel color and pulp firmness indicated that hot water treatment helped to delay banana fruit ripening at both storage conditions. Hot water treatment decreased the levels of hydrogen peroxide (H₂O₂) and malonydialdehyde (MDA) during storage at 25 °C. Glutathione (GSH and GSSG) contents and the ratio of GSH/GSSG during fruit approaching ripening were significantly induced in hot water-treated fruits while ascorbic acid (AA) contents were slightly increased. In addition, the combined treatment increased free phenolics and flavonoids during storage. Results suggest that hot water treatment has led to an induction of antioxidants in banana fruits as indicated by an increase of antioxidants and a decrease of H₂O₂ during ripening, and all of which result in a delayed ripening of banana fruit.