Response of tomato plants to saline water as affected by carbon dioxide supplementation. II. Physiological responses

Summary

Photosynthesis of tomato plants (Lycopersicon esculentum (L.) Mill. cv. F144) was studied under conditions of CO₂ supplementation and salinity. The purpose of the study was to elucidate the mechanisms underlying the effects of salinity on the acclimation of tomato plants to CO₂ supplementation. Plants were grown under either low (355.mmol mol^–1) or elevated (1200.6.50 mmol mol^–1) CO₂ and were irrigated with low concentrations of mixed salts. The highest salinity level (E.C. 7 dS m–1) was that used to produce quality tomatoes in the Negev highlands, in Israel. During early development (three weeks after planting), the net photosynthetic rate of the leaves was much higher under elevated CO₂, and other than a slight decrease in quantum yield efficiency as measured by fluorescence (DF/F 9 ^m ), no signs of acclimation to high levels of CO₂ were apparent. Clear acclimation to high CO₂ concentration was evide t ten weeks after planting when the net photosynthetic rate, photosynthetic capacity, and carboxylation efficiency of leaves of non-salinized plants were strongly suppressed under elevated CO₂. This was accompanied by reductions in carboxylation efficiency, Rubisco activity and PSII quantum yield, and an increased accumulation of leaf soluble sugars. The reduction in photosynthetic capacity in the high CO₂ plants was less in plants grown at the highest salinity level. This was correlated with an increase in the PSII quantum yield parameters (F_v/F_m) and DF/F 9 m ) but not with Rubisco activity which was affected by the CO₂ treatments only. These results explain the effects of high CO₂ on yields in tomatoes grown at high levels of salt (Li et al., 1999).     

Response of eggplants grown in recirculating nutrient solution to salinity imposed prior to the start of harvesting

Summary

The effects of exposing eggplants grown in recirculating nutrient solution to salt stress (6.1 dS m^–1) from planting until the beginning of harvesting, on plant growth, yield and macronutrient status was investigated. The salinity was imposed by adding to a basic nutrient solution either additional nutrients at two cation ratios or NaCl. The results showed that the exposure of plants to salinity prior to the beginning of harvesting reduced both vegetative growth during that time and early fruit yield, but the depression of the latter was more severe. The restriction of the early yield was a result of a reduced mean fruit weight due to a lower fruit water content. The detrimental effects of salinity on the mean fruit weight disappeared 25 d after discontinuing the salinity treatments. As a result, the total yield obtained after five months of harvesting was not influenced by exposing the plants to salinity prior to the beginning of harvesting. The salinity source had no specific effect on plant growth. Moreover, the increase of salinity up to 6.1 dS m^–1 did not cause any specific nutritional imbalance or toxicity to the plants, irrespective of the salts used to achieve it. It is suggested that the electrical conductivity of the nutrient solution may be raised to 6.1 dS m^–1 to control excessive vegetative growth in eggplants grown hydroponically. However, salt treatment should be terminated either at the first harvest, if the total yield is more important than the early yield, or three weeks earlier, if the opposite is true.     

Effect of elevated CO2 on vegetative and reproductive growth characteristics of the CAM plants Hylocereus undatus and Selenicereus megalanthus

This study examined the vegetative and reproductive growth responses of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus and Selenicereus megalanthus to CO₂ enrichment (1000 μmol mol⁻¹ vs. control of 380 μmol mol⁻¹). H. undatus plants enriched with CO₂ demonstrated 52%, 22%, 18%, and 175% increases, relative to plants measured in ambient CO₂, in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. The responses of S. megalanthus plants exposed to elevated CO₂ were greater than those of H. undatus under the same conditions. Compared to plant responses in ambient CO₂, under conditions of CO₂ enrichment, S. megalanthus showed 129%, 73%, 68%, and 233% increases in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. Moreover, for H. undatus, there was no significant change in fruit fresh mass although it showed a slight (7%) upward trend. On the other hand, fruit fresh mass of S. megalanthus significantly increased by 63% in response to elevated CO₂. These results indicate the high potential of CAM plants to respond to CO₂ enrichment. It is thus apparent that S. megalanthus grown under CO₂ enrichment may benefit from elevated CO₂ to a greater extent than H. undatus grown under sub-optimal growth conditions.     

Changes in physicochemical attributes of sweet pepper cv. Domino during fruit growth and development

The effect of harvesting sweet pepper ‘Domino’ fruit at different stages of growth and development on physicochemical attributes was studied. The suitability of fruit fresh weight, diameter and length, weeks from anthesis, total soluble solids (TSS), fruit colour change, firmness, internal CO₂ and C₂H₄ concentrations as well as fruit respiration and ethylene production as maturity indicators were evaluated. Fruits were harvested weekly until fully red ripe. Fruits took 8 weeks after anthesis (WAA) to reach harvest maturity and a further 2–3 weeks to reach full ripeness (11 WAA). Fruits exhibited a sigmoid growth pattern. Hue angle (change in colour from green to red) declined with time while chroma (colour intensity) values increased with fruit maturity, as did TSS. An increase in PⁱCO₂ and PⁱC₂H₄ accompanied the decrease in hue angle. The association between fruit ripening and the significant increase in PⁱC₂H₄ indicates that ethylene may be responsible for ripening of this cultivar of sweet pepper. Colour change and TSS were reasonable indicators of maturity of sweet pepper fruit complemented with fruit firmness.     

Irrigation of Myrtus communis plants with reclaimed water: morphological and physiological responses to different levels of salinity

Summary

The influence of irrigation with different sources of reclaimed water on physiological and morphological changes in Myrtus communis plants was investigated to evaluate their adaptability to such conditions. M. communis plants, growing in a growth chamber, were subjected to four irrigation treatments over 4 months (120 d): a control [tap water (0.8 dS m^–1), leaching 10% (v/v) of the applied water] and three reclaimed water irrigation treatments, namely 1.5 dS m^–1 leaching 25% (v/v) of the applied water (RW1), 4.0 dS m^–1 leaching 40% (v/v) of the applied water (RW2), and 8.0 dS m^–1 leaching 55% (v/v) of the applied water (RW3). After treatment, all plants were irrigated with tap water, as for the control plants, for a further 2 months (60 d). At the end of the first period (4 months), none of the myrtle plants showed any adverse change in biomass and the average total dry weight (DW) increased by 53% in treatment RW2. However, at the end of the treatment and recovery period (180 d), accumulations of Cl^– ions, and especially Na⁺ ions, negatively affected the growth of all RW3 plants. Plants irrigated with all three reclaimed water samples had increased difficulty in taking-up water from the substrate (i.e., they had lower leaf water potential and relative water content values). RW2 plants showed a better response in their gas exchange parameters. The use of reclaimed water decreased leaf K⁺/Na⁺ and Ca²⁺/Na⁺ ratios, but no chlorosis or necrosis were observed. The three reclaimed water samples had different effects on the myrtle plants depending on the specific chemical properties of the water. Leaching was found to be important to minimise the negative effects of salinity in the irrigation water.     

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.     

The Response to CO2 Enrichment of Capillary-Watered Single-Truss Tomatoes at Different Plant Densities and Seasons

CO₂ enrichment advanced the date of first anthesis, promoted earlier cropping and shortened the duration of harvest for single-truss tomatoes sown in December and, to a lesser extent, for those sown in July. It also prevented arrested development of the flowers of a December-sown crop growing in poor light.

CO₂ caused increases in marketable fruit yield that were greatest for a mid- July sowing and least for a mid-December sowing. The increases obtained from plants sown in mid-December were independent of population density. For a mid-July sowing the increases in yield of ripe marketable tomatoes were 33% and 17% at population densities of 10 and 25 plants/m² respectively. Increases in total marketable fruit weight caused by CO₂ resulted from an increase in the number of fruits attaining marketable size and an increase in the average weight of individual fruits.

Some of the advantages of producing fruit on single-truss tomatoes grown in shallow capillary-watered beds are mentioned.     

Evaluation of Salinity Tolerance of Some Selected Almond Genotypes Budded on GF677 Rootstock

ABSTRACT

In order to evaluate the tolerance of some almond genotypes to salinity, a factorial experiment was carried out based on completely randomized design (CRD), with two factors: genotypes in 11 levels (Tuono, Nonparaeil, Mamaie, Shokoufeh, Sahand, ‘Ferragnès,’ 1–16, 1–25, A₂₀₀, 13–40 budded on GF₆₇₇ rootstock, and GF₆₇₇ (without budding)) and irrigation water salinity in five levels (0, 1.2, 2.4, 3.6, and 4.8 g/l of natural salt (equal electrical conductivity 0.5, 2.5, 4.9, 7.3, and 9.8 dS/m, respectively) and with 4 replication for each treatment in research greenhouse of Seed and Plant Institute in years 2013 and 2014. The results showed that with increasing salinity concentration, growth indicators include the branch height, branch diameter, number of total leaves, percentage of green leaves, leaf density on the main branch, leaf area and leaf area ratio, relative humidity content, chlorophyll index, chlorophylls a, b, total, scion fresh and dry weight, root fresh and dry weight have been reduced in the all genotypes studied, but percentage of necrotic leaves, percentage of downfall leaves, root fresh and dry weight ratio to scion fresh and dry weight, relative ionic percentage, and cell membrane injury percentage of leaves were increased. The results of chlorophyll fluorescence showed that salinity stress affected on the young trees by increasing the amount of minimum fluorescence (F_O) and decreasing the maximum fluorescence (F_m) and reduced variable fluorescence (F_v) in the plants and reduced variable fluorescence ratio to maximum fluorescence of 0.83 in the control plants to 0.72 in Sahand cultivar and GF₆₇₇ rootstock. The result showed that type of scion was affected in obstruction of Na⁺ absorption by the roots and their transported to leaves, as well as was affected in increasing uptake of K⁺ by the roots and their transported to leaves. In this research, GF₆₇₇ is well tolerated to water salinity to 4.9 dS/m but with higher range of salinity showed stress effects. The result showed that type of genotypes budded on GF₆₇₇ rootstock was very effective in tolerant to salinity. Overall, ‘Ferragnès’ was recognized as the most tolerant cultivar to salinity stress. This cultivar could tolerate salinity 3.6 g/l (Ec: 7.3 dS/m). Also, Sahand was recognized as the most sensitive cultivar to salinity stress.     

Salinity tolerance of bermudagrass (Cynodon spp. L. C. Rich) cultivars and shoot Na,K and Cl contents under a high saline environment

Summary

Increasing need for salt-tolerant turfgrasses continues due to population growth in arid and semi-arid regions where potable water is limited, while soil and existing water sources are salty. Bermudagrass (Cynodon spp. L. C. Rich) is widely used in these areas. Therefore, this experiment was conducted to evaluate the salt-tolerance of ten cultivars of bermudagrass under a high saline soil and water environment. Five salinity levels of irrigation water (3.30, 6.93, 10.2, 14.8 and 17.8 dS m^–1) were prepared and 30 pots were surfaced-irrigated at each salinity level for 1 year. Overall top growth, root growth, K content and K:Na ratio were reduced by 75%, 45%, 77% and 94.5%, respectively; while leaf-firing, shoot Cl and shoot Na concentrations were increased by 4%, 498% and 356%, respectively, when the salinity increased from 3.3 dS m^–1 to 17.8 dS m^–1. Regarding the salt-tolerance of cultivars, ‘Tifway’ was superior in top growth, percentage leaf-firing, Na uptake and K:Na ratio, ‘ISF2’ in root growth, and ‘Tifdwarf’ in Cl uptake. Although ‘Tifway’ showed the greatest reduction in root dry weight, it had the lowest level of leaf-firing and lowest reduction in top growth, which could be due to having the lowest Na uptake. Cultivars exhibited marked differences in their response to salinity; however, no mortality was observed, indicating that all cultivars tolerated the salinity levels used in the experiment.     

Growth characteristic and sink strength of fruit at different CO2 concentrations in a Japanese and a Dutch tomato cultivar

The aim of the present study was to elucidate how fruit growth was limited by the source and sink capacities in a Japanese (‘Momotaro York’) and a Dutch (‘Dundee’) tomato cultivar. The two cultivars were grown hydroponically with a high-wire system in greenhouses for 25 weeks, and the growth characteristics and sink strength of fruit were determined. Fruits were pruned to four (4F) or one (1F) per truss. The latter were used to determine potential fruit growth, an indicator of fruit sink strength. Growth was also determined under normal (LC) and enriched (HC, 700 μmol mol⁻¹) CO₂ concentrations to examine the effect of source enhancement on fruit production. In both cultivars under normal CO₂, the growth rate of fruit pruned to 4F per truss was lower than that in 1F, indicating that maximum potential fruit growth was not achieved. Under HC conditions, fruit growth rate of ‘Dundee’ achieved in 4F trusses was lower than that in 1F. In ‘Momotaro York’ in HC, fruit growth in 4F trusses was close to potential. This implies that fruit growth was source-limited irrespective of CO₂ concentrations in ‘Dundee’ cultivar while fruit growth in ‘Momotaro York’ under normal and enriched CO₂ conditions was limited by source and sink strengths, respectively. Adjustments of cultural practices including increasing fruit number per truss and/or genetic approaches to enhancing fruit sink strength by breeding may improve fruit yields of Japanese cultivars under high source/sink conditions.     

The Effects of Manurial Treatments on the Chemical Composition of Gooseberry Bushes.: I. Effects on Dry Matter,Ash and Ash Constituents of Leaves and Stems of Terminal Shoots and of Fruits; and on Total Nitrogen of Fruits.

Summary

The effects of different timings of fruit thinning at the lower nodes (nodes 4 to 7) on fruit growth and abortion at higher nodes were investigated in a gynoecious, parthenocarpic cultivar of cucumber (Cucumis sativus L.), ‘NK x AN8’. Fruits at the lower nodes were removed 0, 5, 10, 15 and 20 d after anthesis of flowers at node 8 (DAA₈).

Total leaf areas and growth patterns of individual fruit were then monitored. When fruits at nodes 4 to 7 were thinned 0 or 5 DAA₈, all fruits at nodes 8 to 12 grew to commercial size, without fruit abortion. When fruits were thinned 10 DAA₈, the fruits at nodes 8 to 12 ceased to grow after anthesis, but growth was restored a few days after fruit thinning. Fruit thinning at 15 or 20 DAA₈ forced most fruits at nodes 8 to 12 to abort, while fruits at node 13 and above ceased to grow for a while, but resumed growth after fruit thinning. In all treatments, total leaf area increased with time throughout the experiment. High fruit load depressed the rate of growth of leaf area slightly, 65 to 75 d after sowing. Fruit load (fresh weight) per leaf area was about 50 mg cm^–2 just before fruits at nodes 4 to7 were thinned at 20 DAA₈.These results suggest that fruit abortion occurs if fruits at the lower nodes persist for a long period, and fruits at the middle nodes senesce before enlargement. Fruit thinning at the lower nodes can restore the growth of fruits in the stagnant growth phase within 10 d.     

Physical and cellular structure changes of Rastali banana (Musa AAB) during growth and development

A study on the physical and physiological characteristics of Rastali bananas (Musa AAB) was carried out throughout the 12 weeks after emergence of the first hand to determine the optimum growth stage of Rastali bananas. The fruit length and diameter followed a trend similar to that observed in fruit fresh weight throughout fruit development, and three physiological stages (S1–S3) of sigmoid growth were identified. The growth rate was slow during S1 (1st to 4th week), rapid during S2 (5th to 10th week) and remained constant during S3 (11th and 12th week). Peel cells underwent periclinal growth, which was accompanied by an increase in fruit peel and pulp thickness as the fruit developed. Moreover, the pulp colour became more vivid and yellow as the fruit developed. The peel moisture content decreased while pulp moisture content increased during fruit growth and development. The pulp firmness increased from the first until seventh week, and it decreased from the seventh week until twelfth week of the experiment. Carbon dioxide (CO₂) production was the highest at S1. However, CO₂ production declined until the 10th week and remained constant at a low level of 50 mL kg⁻¹ h⁻¹ during S3. Ethylene (C₂H₄) could not be detected throughout fruit growth and development. Thus, Rastali bananas showed physiological maturity at week 11 and week 12 after emergence of the first hand with constant fruit growth.     

Effect of Carbon Dioxide Enrichment on Growth,Development and Yield of Glasshouse Tomatoes. II. The Duration of Daily Periods of Enrichment

The effects of various daily durations of CO₂ enrichment ‘on early-sown glasshouse tomatoes are outlined. Reducing the daily enrichment period in the pre-planting stage (late November to mid-January) had only marginal effects on total yields and · monetary values. Reductions in the post-planting stage (mid-January to mid-April) caused significant depressions in yields, roughly proportional to the · reduction in enrichment time. For a given reduction in the duration of daily enrichment, delaying the start of enrichment in the morning was more detrimental than ending it prematurely before sunset.

Varying the frequency of water applications during the CO₂ enrichment period, from every second to every eighth day, had little effect, with no significant interactions between enrichment duration and watering frequency.

Daily durations of CO₂ enrichment somewhat shorter than the full sunrise-sunset periods, during the pre-planting stage, may not significantly reduce the total returns from the crop, but the consequent monetary saving would be quite small. Any reduction during the post-planting stage would be detrimental, resulting in a far greater loss in revenue than the consequent saving in costs.     

Effect of different light intensities on the photosynthate distribution in cherry tomato seedlings

To investigate the effect of varying the light intensity on the photosynthate distribution, cherry tomato (Solanum lycopersicum L.) seedlings were grown under different light intensities. It was found that the seedlings under 300 μmol m^–2 s^–1 had a significantly higher dry weight and health index (Health index = Stem diameter/Stem height × Dry weight) than seedlings receiving other light treatments. On the contrary, the biomass, specific leaf mass and health index values of seedlings exposed to 50 μmol m^–2 s^–1 and 550 μmol m^–2 s^–1 were the lowest among all of the treatments. In terms of ¹⁴C-labelled photosynthate translocation, the seedlings under 300 μmol m^–2 s^–1 had lower remaining ¹⁴C-labelled photosynthate (31.45%) compared with other treatments, after ¹⁴CO₂ was supplied for 2 days. The seedlings under 150 μmol m^–2 s^–1 had 36.97% of ¹⁴C-labelled photosynthate in the labelled leaves and transported the obviously higher ¹⁴C-labelled photosynthate to new shoot than others. Together, our results indicate that the photosynthate distribution was the most rational in cherry tomato seedlings at 300 μmol m^–2 s^–1, which enhanced leaf photosynthesis and plant growth.     

Effects of the application of ‘cash’ on the growth,fruit yield,and nutrient status of tomato (Solanum lycopersicum L.) grown in reclaimed saline soil

Summary

The effects of ‘cash’ [a novel 2:5:1 (w/w/w) mixture of calcium sulphate, ground sunflower heads, and humic acid] as a soil amendment on the growth, fruit yield, and leaf nutrient status of tomato (Solanum lycopersicum L.) grown on reclaimed saline soil (EC = 9.4 dS m^–1) were investigated. A glasshouse experiment was performed in a completely randomised design with six treatments (0, 10, 20, 30, 40, or 50 g ‘cash’ kg^–1 soil) each with four replicates. The results indicated that ‘cash’ increased both the shoot dry weight (DW) plant^–1 and the root DW plant^–1, the free proline contents of leaves, and leaf chlorophyll contents. The use of ‘cash’ also increased the number of fruit plant^–1, fruit yield pot^–1, and fruit vitamin C contents, although total soluble solids (TSS) contents were not affected. The contents of nitrogen (N), potassium (K), and calcium (Ca), and the Ca:Na ratios of leaf tissues increased with all application rates of ‘cash’. Leaf phosphorus (P) contents showed no response to any applied level of ‘cash’. Leaf sodium (Na) contents declined gradually with an increase in the level of ‘cash’ applied to the soil. We concluded that ‘cash’ has a pronounced positive effect on the growth and fruit yield of tomato plants grown in reclaimed saline soil. ‘Cash’ therefore has the potential to be used as a soil amendment for vegetable crops such as tomato to overcome the adverse effects of salinity in newly-reclaimed soils.     

Effects of salinity at two ripening stages on the fruit quality of single-truss tomato grown in hydroponics

Summary

Single-truss tomato plants grown hydroponically (wet-sheet culture) were exposed to a salinity (EC) of 5.0 dS m²¹ or 8.0 dS m²¹ at two fruit ripening stages, the immature green stage and the decolouring stage. These salinities were achieved by adding NaCl to the standard solution, which had an EC of 2.4 dS m²¹. Increased salinity at the immature green stage improved fruit quality more than increased salinity at the decolouring stage but decreased fruit yield more. The reduction in fruit yield was due to a decrease in fruit weight but not in fruit number. Salinity increased the concentration of soluble solids, citrate, ascorbic acid, K, chlorophyll a, chlorophyll b, lycopene, and carotene in the fruit, but the absolute amount of these constituents per fruit was decreased or not affected. These results suggest that the improvement in fruit quality induced by the salinity is caused by the reduction of water import into the fruit. The effectiveness of both salinities was significantly bigger when it was applied at the earlier development stage, suggesting that mature fruit would be less sensitive to strength of the EC.     

Modified atmosphere packaging of minimally processed avocado cv. ‘Booth 7’

Summary

Avocado fruits were washed with 200 µg l^–1 active chlorine, partially ripened to a firmness of about 12.5 ± 0.6 kg cm^–2, and sliced. Fruit slices were dipped in 1.0 mg l^–1 citric acid and 200 µg l^–1 ascorbic acid maintained at 4°–6°C for 2 min, dried with tissue paper and packaged in 0.05 mm or 0.075 mm-thick low density polyethylene (LDPE) at a 1:1 surface area to product weight ratio (cm² g^–1). Sodium chloride (1 g) sealed in 0.075 mm-thick poly-coated paper pouches was included in the packages for moisture absorption. In-package O₂ and CO₂ concentrations, as well as the ethanol and acetaldehyde concentrations, firmness and lightness (L^* value) of the tissue slices were measured during storage for 10 d. The sensory attributes of the modified atmosphere (MA)-packaged slices were compared with fresh fruit slices. In-package O₂ concentrations fell from 14.1% to 6.3% and CO₂ concentrations rose from 4.7% to 4.9%. Ethanol concentrations increased from 9.0 to 32.1 µg g^–1 and acetaldehyde from 1.1 to 3.8 µg g^–1 during storage from day-1 to day-10 in the 0.05 mm-thick LDPE with sodium chloride moisture absorbers. In-package concentrations of O₂ fell from 10.8% to 3.8% and CO₂ rose from 3.8% to 8.1%, while ethanol concentrations increased from 10.0 to 40.4 µg g^–1 and acetaldehyde from 1.3 to 4.7 µg g^–1 during storage from day-1 to day-10 in the 0.075 mm-thick LDPE with sodium chloride moisture absorbers. The L^* value and sensory attributes of avocado slices packaged in 0.05 mm-thick LDPE, with moisture absorbers, were not significantly different from fresh slices, indicating the effectiveness of these MA conditions. Regardless of packaging conditions, avocado slices reached the firmness values of 5.8–6.3 kg cm^–2 required for the ‘table-ripe’ stage on day-10 in storage. Therefore, packaging of ‘Booth 7’ avocado slices in 0.05 mm-thick LDPE with sodium chloride as a moisture absorber resulted in a storage-life of 10 d at 8°C and 90 ± 2% RH.     

Controlled-atmosphere storage of kiwifruit. I. Effect on fruit firmness and storage life

The effect of atmospheres containing high CO₂ and low O₂ on the firmness of kiwifruit (Actinidia chinensis Planch.) during cool storage at 0°C has been studied. Atmospheres containing above 4% CO₂ with 15–20%O₂ caused a retardation in the softening of kiwifruit. This effect increased as the CO₂ content of the atmosphere increased from 4 to 10%, but additional CO₂ above 10% had no further effect on fruit firmness. Low O₂ (2–3%) with 3–5% CO₂ further delayed the rate of kiwifruit softening and increased storage life up to 3–4 months beyond normal air-storage life. Although controlled-atmosphere storage increases storage life of kiwifruit, the magnitude of the effect was found to vary from year to year. Contamination of the storage atmosphere by as little as 0.1 μl^?1 ethylene severely reduced the effectiveness of controlled-atmosphere storage in maintaining kiwifruit firmness, even at 0°C.     

Net CO2 exchange rate of in vitro plum cultures during growth evolution at different photosynthetic photon flux density

CO₂ concentration was monitored during three 15-day subculturing cycles in vessels containing actively proliferating plum cultures of Prunus cerasifera, clone Mr.S. 2/5. The effects of two photosynthetic photon flux density regimes: 50 ± 5 μmol m⁻² s⁻¹ and 210 ± 5 μmol m⁻² s⁻¹ were compared. Three distinct phases in the CO₂ trend were distinguished during each culturing cycle of both light treatments. In the first, occurring at the beginning of the culture cycle, the amount of CO₂ emitted by the cultures during dark periods was greater than that assimilated during the light periods. In the second phase, the opposite trend was detected, while in the third, the range of CO₂ day–night fluctuations increased or remained stable according to the number of explants per vessel. The treatment with 210 ± 5 μmol m⁻² s⁻¹ did not modify the CO₂ phase trend but induced more pronounced fluctuations in day–night CO₂ concentration. Under this light treatment, cultures reached CO₂ compensation point for a period as long as 48% of the total number of light hours, while under 50 ± 5 μmol m⁻² s⁻¹, it was only 8%. The different range in CO₂ day–night fluctuations monitored throughout a subculturing cycle, appeared to be mainly induced by changes in culture growth dynamics.     

Fruit development and ripening in Barbados cherry,Malpighia emarginata DC.

Barbados cherry fruit shows a biphasic pattern of growth whether monitored on a diameter or weight basis. Each growth phase was of about 2 weeks duration with weight gains of equal magnitude but with most of the size increase occurring in the first phase. Pyrene growth paralleled that of the whole fruit. Cell division was limited to the first week of fruit development and horticultural maturity was reached when fruit showed colour break (18 days post-anthesis). Barbados cherry is climacteric with a very high peak respiratory rate (900 ml CO₂ kg⁻¹ h⁻¹) but a low rate of peak ethylene production (3 μl C₂H₄ kg⁻¹ h⁻¹), the former consistent with its high perishability.