Decay of muskmelons stored in controlled atmospheres

Musk melons, Cucumis melo L. var. reticulatus Naud., (commonly referred to as cantaloupes) stored for 14 days in $\text{20\%}\text{CO}{}_2\text{21\%}\text{O}{}_2$ at 5°C plus 3 days in air at 20°C, had less stem scar mold, surface mold, and flesh decay than those held in air or in $\text{5}\text{or}\text{10\%}\text{CO}{}_2\text{21\%}\text{O}{}_2$. Forty percent $\text{CO}{}_2\text{21\%}\text{O}{}_2$ appeared to injure the melons and cause off-odors and off-flavors. Storage in 1, 2, 4 or 8% O₂ for 14 days did not reduce mold growth, as compared with air storage.     

Photosynthetic characteristics and protective mechanisms against photooxidation during high temperature stress in two citrus species

Exposure of Satsuma mandarin (Citrus unshiu Marc.) and Navel orange (Citrus sinensis Osbeck) plants to high temperature (38 °C) led to reductions of the net photosynthetic rate (Pn), the photorespiration rate (Pr), the quantum efficiency CO₂ assimilation (ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$), the maximal photochemical efficiency of PS2 (Fv/Fm), the photochemical quenching (qP) and the quantum efficiency of PS2 photochemistry (Φ_PS2), whereas the minimal fluorescence yield (Fo) and the non-photochemical quenching (qN) increased. Increase in the value of Pr/Pn and ΦPS₂/ΦCO₂${\Phi }_{\text{PS}2}/{\Phi }_{\text{C}{\text{O}}_2}$ was attributed to the greater decrease in Pn and ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$ than Pr and Φ_PS2. In addition, the superoxide radical (O₂⁻) production, the H₂O₂ concentration and the activities of antioxidant enzymes such as the superoxide dismutase (SOD, EC 1.15.1.1), the ascorbate peroxidase (APX, EC 1.11.1.11), the dehydroascorbate reductase (DHAR, EC 1.8.5.1) and the catalase (CAT, EC 1.11.1.6) were raised. On the other hand, the chlorophyll concentration in leaves decreased during high temperature stress. These results suggest that decline in Pn related to inactivation of PS2 reaction centers may be due to the enhanced number of active oxygen species in the citrus leaves. The water–water cycle may play a role in limiting the degree of photodamage caused by high temperature. Lower O₂⁻ production rate, the H₂O₂ concentration and the antioxidant enzymes activity were observed in high temperature tolerant species of citrus. The exogenous active oxygen scavenger ascorbic acid (Asc) enhanced the ability to clear the O₂⁻ in citrus plants, and quicken the recovery of photosynthetic apparatus.     

Effects of ozone and sulfur dioxide on grapevines

Greenhouse-grown ‘Ives’ and ‘Delaware’ grapevines (Vitis labruscana, Bailey) were fumigated for 4-hours with ozone (O₃) and/or sulfur dioxide (SO₂) at 0.40 and 0.80 mg l^?1. Fumigations were performed in a plexiglass chamber situated within a controlled environment walk-in growth chamber. When applied separately, both gases induced characteristic foliar injury. ‘Ives’ grapevines were much more sensitive to $\text{O}{}_3\text{SO}{}_2$ fumigations than were ‘Delaware’ grapevines. Within each cultivar, leaf necrosis and shoot growth reduction were greatest following fumigation with 0.80 mg l^?1 O₃ plus 0.80 mg l^?1 SO₂. Leaf abscission occurred only on ‘Ives’ and was related to foliar necrosis. Shoot growth following fumigation was less on vines having most foliar necrosis. Yet, ‘Delaware’ vines showing less than 1% leaf area necrosis still had significant reductions in shoot growth. All O₃ and SO₂ fumigations resulted in stomatal opening.     

Effects of gaseous compounds in smoke on dormancy release in freesia corms

Exposing corms to smoke generated from smouldering plant materials (“smoke treatment”) releases freesia corms from dormancy. The smoke was found to contain some hydrocarbons, i.e. ethane, ethylene, (C₂H₄), and propylene at concentrations below 130 μl 1^?1, and carbon monoxide (CO) at 2000-400 μl 1^?1.Exogenous C₂H₄ at low levels of 100-1 μl/litre air strongly stimulated dormancy-release. In contrast, propylene and acetylene were required at a concentration much higher than that in the smoke to exert the dormancy-releasing effect: the application of 100 μl/litre air had little or no effect. Air containing $\text{1000 μ}\text{l CO}\text{litre}$ air produced some effect, which could be masked by co-existence of $\text{10 μ}\text{l C}{}_2\text{H}{}_4\text{litre}$ air. Acetaldehyde, which may occasionally be present in smoke, showed the dormancy release at ca. 1 mM but was phytotoxic. Corms exposed to smoke or C₂H₄ did not show an endogenous C₂H₄ rise, while non-treated corms showed it distinctly before dormancy release.These results suggest that a C₂H₄-stimulus is dominant in smoke treatment.     

Models of water competition between fruits and leaves on spurs of ‘Bartlett’ pear trees and its measurement by a heat-pulse method

Water streams through the conducting systems in spurs of ‘Bartlett’ pear trees were modelled in piped water-streams or electric currents, and measured by a heat-pulse method. Water-potential measurements showed that water potentials of stems (ψ_s), leaves (ψ_l) and fruits (ψ_f) were highest, lowest and intermediate, respectively, at mid-day throughout fruit growth. Retaining this condition (ψ_s >ψ_f >ψ_l), a model was constructed where streams of water through pipes connecting 3 tanks with different water-levels was analogous to water streams among 3 organs of a spur. It was then possible to estimate the possibility of water flowing from the fruit into the leaf against a reverse gradient of water-potential between the stem and the fruit. Another model used electric currents passing through 3 connected electric cells with different voltages. As the electric resistances of the 3 paths were equal, the voltage gradients toward each cell in the circuit were calculated using Kirchhoff's law. Replacing voltages by water potentials allowed the gradients of water potential toward each organ to be estimated, $\text{2}\text{3}\text{ψ}{}_{\mathrm{<mtext>l</mtext>}}\text{?}\text{1}\text{3}\text{(ψ}{}_{\mathrm{<mtext>s</mtext>}}\text{+ ψ}{}_{\mathrm{<mtext>f</mtext>}}\text{)}$ toward the leaf, $\text{2}\text{3}\text{ψ}{}_{\mathrm{<mtext>f</mtext>}}\text{?}\text{1}\text{3}\text{(ψ}{}_{\mathrm{<mtext>s</mtext>}}\text{+ ψ}{}_{\mathrm{<mtext>l</mtext>}}\text{)}$ toward the fruit and $\text{2}\text{3}\text{ψ}{}_{\mathrm{<mtext>s</mtext>}}\text{?}\text{1}\text{3}\text{(ψ}{}_{\mathrm{<mtext>l</mtext>}}\text{+ ψ}{}_{\mathrm{<mtext>f</mtext>}}\text{)}$ toward the stem of the spur. Adverse water fluxes from fruits (for instance, ?0.5 ml peduncle^?1 h^?1 at the maximum rate) were determined by a heat-pulse method at mid-day in early August. Demonstrations of water fluxes through the peduncles and the petioles by this method gave close agreement with results from the 2 models in relation to the diurnal shifts of direction of the water streams. The gradients of water potential estimated by the electric current model was closely related to water fluxes during the day (r = ?0.9832 for peduncles, r = ?0.9604 for petioles). Hydraulic conductivities (L_p) for petioles or peduncles were in the order of 10^?4 cm s^?1 bar^?1.     

The effect of defoliation on bulb production of tulip cultivar ‘Apeldoorn’

The distribution of dry matter between the different bulblets of tulip is not markedly influenced by either changes in leaf area or the position of the leaf. On the contrary, total bulb yield is strongly affected.A reduction factor, S_c, for incomplete soil coverage, when the leaf area index (LAI) is less than 4, normally used for evaluation of planting density effects, can also be used for the effects of defoliation on dry matter increase. This LAI-dependent factor shows a distinctly asymptotic pathway closely resembling

$\text{S}{}_{\mathrm{c}}\text{=}\text{P}{}_{\mathrm{act}}\text{P}{}_{\mathrm{pot}}\text{=1?e}{}^{\mathrm{?k1LAI}}$

where k ～ 0.6 and in which P_act is the actual measured dry weight increase and $\text{P}\text{?}{}_{\mathrm{<mtext>pot</mtext>}}$ the potential net dry weight increase for a closed canopy.     

Additional nitrogen fertilization affects salt tolerance of lemon trees on different rootstocks

Irrigation with saline water is one of the major problems in citrus crop in arid and semi-arid regions. Because rootstock and fertilization play an important role in citrus salt tolerance, we investigated the influence of the nitrogen fertilization and rootstock on salt tolerance of 2-year-old potted Fino 49 lemon trees. For that, trees grafted on Citrus macrophylla (M) or Sour orange (SO) rootstocks were watered for 12 weeks with complete nutrient solution containing either 0 mM NaCl (control, C), 50 mM NaCl (S), 50 mM NaCl with an additional 10 mM potassium nitrate (S + N), or 50 mM NaCl with a 1% KNO₃ (S + Nf) foliar spray application. Trees on M were more vigorous than trees on SO and saline treatments reduced leaf growth similarly in trees on both rootstocks. Trees on SO had a lower leaf Cl⁻ and Na⁺ concentration than those on M. Additional soil nitrogen (S + N) decreased leaf Cl⁻ concentration and increased leaf K⁺ concentration in salinized trees on both rootstocks. However, the salinity-induced reduction leaf growth was similar in S + N and S trees. This was due to osmotic effect, beside leaf Cl⁻ and Na⁺ toxicity, played an important role in the growth response of Fino 49 lemon to the salt stress. Additional foliar nitrogen in the S + Nf treatment also reduced leaf Cl⁻ concentration relative to the S treatment but trees from S + Nf treatment had the lowest leaf growth. Net assimilation of CO₂ (ACO₂$A_{\text{C}{\text{O}}_2}$), stomatal conductance (g_s) and plant transpiration were reduced similarly in all three salt treatments, regardless rootstock. Salinity reduced leaf water and osmotic potential such that leaf turgor was increased. Thus, the salinity-induced ACO₂$A_{\text{C}{\text{O}}_2}$ reductions were not due to loss of turgor but rather due to high salt ion accumulation in leaves.     

Temperature influences nutrient absorption and uptake rates of bananas grown in controlled environments

We explored the influence of temperature on the concentration of nutrients in banana plants, the nutrient uptake rate, apparent root transfer coefficient ($\text{}\text{?}$ga) and the relationship between accumulation of dry matter and nutrient. Young banana plants (Musa (AAA group, Cavendish sub-group) ‘Williams’) were grown at six temperature regimes (17/10–37/30°C) in sunlit growth chambers for 12 weeks.The amount of nutrient absorbed was influenced by the amount of growth made, but the link between the two differed from one element to another. Temperatures less than $\text{29}\text{22°}\text{C}$ reduced the concentration of all elements in the whole plant, except Fe.Temperature influenced the root uptake rate of B 10-fold; K, Na, Ca, Fe and Zn 3–4-fold; and N, P, Mg, Mn, Cu, Cl 1–2-fold. Among the elements the highest recorded rate was 12 mg g^?1 day^?1 for K at $\text{33}\text{26°}\text{C}$. The optimum temperature for nutrient uptake rates differed among the elements. This was accounted for largely by greater growth at those temperatures of organs with high concentration of particular elements.The $\text{}\text{?}$ga (an estimate of efficiency of uptake) of B varied 12-fold among treatments; K, Ca, Mg, Na, Mn, Zn and Cl varied 3–5- fold and N, P, Cu and Fe varied 2–3-fold.The ratio of relative nutrient accumulation rate, R_m, to the relative growth rate, R_w, was most stable across temperatures for N and least stable for B and Na. However, the trend was for $\text{R}{}_{\mathrm{<mtext>m</mtext>}}\text{R}{}_{\mathrm{<mtext>w</mtext>}}$ to increase as temperature rose, indicating an absorption of nutrients greater than might be expected from a change in growth rate as temperature increased, and a decreased efficiency in their utilization for plant growth.     

Relationship between bolting-resistance and seed dormancy of different celery cultivars

A correlation between bolting-resistance and seed dormancy was established for 13 celery cultivars. Those cultivars which bolted early in response to a 4-week cold-treatment (7°C) given at the 5-leaf seedling stage had seeds which gave a high germination response to $\text{GA}{}_{\mathrm{<mtext>4</mtext><mtext>7</mtext>}}$ at 2 × 10^?4M in the dark at 22°C. Conversely, bolting-resistant cultivars showed a low germination response to $\text{GA}{}_{\mathrm{<mtext>4</mtext><mtext>7</mtext>}}$. A correlation coefficient (r) of 0.969 was calculated from these data, and values of r = 0.947 and r = 0.950 were obtained using data from field trials on celery bolting in 1974 and 1975, respectively.     

Modelling the effect of air vapour pressure deficit on leaf photosynthesis of greenhouse tomatoes: The importance of leaf conductance to CO2

Summary

The response of photosynthesis of leaves of greenhouse tomato plants to leaf position and vapour pressure deficit (VPD) was studied by modelling the effect of these on leaf conductance to CO₂. The study was carried out in Avignon (southern France) on well-irrigated plants during spring and summer seasons, with VPD ranging from 0.7 to 3.4 kPa at midday, while the 24 h mean ranged from 0.6 to 1.8 kPa. Net photosynthesis (Pn) was measured on single leaves placed at three levels defined by the leaf position, and under different CO₂ concentrations in the range of 200 to 1100 µmol mol^–1. A model for leaf photosynthesis was used to evaluate the leaf conductance to CO₂ transfer. The leaf conductance to CO₂ transfer was maximum for top level leaves, and decreased with leaf depth in the canopy. Leaf conductance at the upper level was reduced when air VPD exceeded a threshold value of 1 kPa.     

Effect of reducing the infrared radiation of sunlight on greenhouse temperature,leaf temperature,growth and yield

Infrared radiation, which is responsible for leaf temperatures that exceed the optimal for photosynthesis, was reduced by absorption in an aqueous CuSO₄ solution. A small greenhouse was constructed of double acryl plates through which a 0.5% CuSO₄ solution was circulated for infrared radiation filtration and cooling. The air temperature in this greenhouse never exceeded 30° C and the leaf temperature of the plants grown in this house was 10% lower than in a glass greenhouse. The yield of tomato plants grown in the acryl greenhouse, with infrared radiation filtration and receiving CO₂ enrichment during the entire light period, was not significantly increased as compared with the yield in the glass greenhouse with a similar CO₂ concentration. This may have been due to long periods with low light levels caused by extremely rainy and cloudy weather conditions, and by condensation on the inside surfaces of the acryl greenhouse caused by the high humidity.     

Effects of shoot size,number of continuous-light cycles and solar radiation on flower initiation in the carnation

Carnation plants (Dianthus cary ophyllus L.) cultivar ‘White Sim’, were grown in containers in a glasshouse under short (8 h) days. When the primary shoots had 4, 8 or 12 pairs of visible leaves, the plants were moved to a continuous-light area, lit by tungsten lamps for 5, 10, 15 or 30 days, and then returned to short days. This was repeated with several sets of plants at different times of year to obtain a range of radiation flux densities.The number of continuous-light cycles required to initiate a given proportion of shoots was dependent upon the radiation integral, a generalised linear model gave quantitative relationships between the proportion of responding shoots, the number of cycles of continuous light (CL) and the radiation integral. For shoots with 4 visible leaf pairs the model

$\text{keta;=μ+∝X}{}_1\text{+βX}{}_2$

accounted for 83% of the deviance, where η is the linear predictor, μ, α and β are parameters, X₁ = log_e (number of CLs + 1) and X₂ = log_e mean radiation (calories cm^?2 day^?1). For shoots with 8 visible leaf-pairs, 76% of the deviance was removed.Under low radiation integrals, intra-plant competition resulted in only a small proportion of shoots on a plant initiating flowers; increasing the number of CL cycles only partially mitigated this effect. At low radiation integrals, shoots that failed to initiate flowers in CL were often delayed by this treatment and initiated flowers later than shoots in short days. Both the CL-requirement and the limiting effect of the radiation integral on the proportion of shoots that initiated flowers decreased as shoot size increased.It is concluded that competition for photosynthetic assimilates under low radiation conditions can severely limit flower initiation in the carnation.     

Does root-sourced ABA play a role for regulation of stomata under drought in quinoa (Chenopodium quinoa Willd.)

The Andean seed crop quinoa (Chenopodium quinoa Willd.) is traditionally grown under drought and other adverse conditions that constrain crop production in the Andes, and it is regarded as having considerable tolerance to soil drying. The objective of this research was to study how chemical and hydraulic signalling from the root system controlled gas exchange in a drying soil in quinoa. It was observed that during soil drying, relative g_s and photosynthesis A_max (drought stressed/fully watered plants) equalled 1, until the fraction of transpirable soil water (FTSW) decreased to 0.82 ± 0.152 and 0.33 ± 0.061, respectively, at bud formation, indicating that photosynthesis was maintained after stomata closure. The relationship between relative g_s and relative A_max at bud formation was represented by a logarithmic function (r² = 0.79), which resulted in a photosynthetic water use efficiency WUE_Amax_/gs$\text{WU}{\text{E}}_{A_{\text{max}}/g_{\text{s}}}$ of 1 when FTSW > 0.8, and increased by 50% with soil drying to FTSW 0.7–0.4. Mild soil drying slightly increased ABA in the xylem. It is concluded that during soil drying, quinoa plants have a sensitive stomatal closure, by which the plants are able to maintain leaf water potential (ψ_l) and A_max, resulting in an increase of WUE. Root originated ABA plays a role in stomata performance during soil drying. ABA regulation seems to be one of the mechanisms utilised by quinoa when facing drought inducing decrease of turgor of stomata guard cells.     

Water relations between leaf water potential,photosynthesis and agronomic vine response as a tool for establishing thresholds in irrigation scheduling

During the last few years, leaf water potential has been a useful tool in controlling vine water status. However, the time of measurement that could best explain short- and long-term vine responses remains a matter of discussion. The objectives of this work were to study the relationship between vine water status and vine performance and to determine what time of day leaf water potential is best correlated to physiological performance and agronomic vine response. The assay was conducted in Madrid, Spain. Plant material was Cabernet-Sauvignon (Vitis vinifera L.) grafted onto SO₄. Three irrigation treatments were established: T1 was non-irrigated, and T2 and T3 were irrigated with a constant fraction of the ETo, k = 0.45 and 0.2, respectively. Vine water status was monitored through predawn, midmorning and noon leaf water potential. Their relationships with net CO₂ assimilation rate, vegetative growth rate, yield components and must composition at harvest were studied for 3 consecutive years. Shoot growth rate and net CO₂ assimilation rate were better correlated with midmorning and noon leaf water potentials – Ψ_m and Ψ_n – than predawn leaf water potential – Ψ_pd – but all of them were significant. Shoot growth rate was zero for Ψ_pd = −0.48, Ψ_m = −1.12 and Ψ_n = −1.18 MPa. Berry size was better correlated with the water stress integral for predawn (S_Ψpd$S_{{\Psi }_{\text{pd}}}$) although the water stress integral for midmorning (S_Ψm$S_{{\Psi }_{\text{m}}}$) and noon (S_Ψn$S_{{\Psi }_{\text{n}}}$) performed quite well. No relationship was found between the water stress integral and TSS, total acidity or pH. Leaf water potential performed as a good parameter for determining both vine water status and agronomic response, but not for evaluating must composition.     

The effects of pre-sowing seed treatments on the germination and emergence of lettuce seeds at high salt concentrations

Radicle emergence in lettuce seeds cultivar ‘Hilde’ was reduced by NH₄NO₃ above 8×10^?2M, while radicle extension was inhibited by 8×10^?2M NH₄NO₃ and no seedlings emerged. Inhibition of radicle emergence by 8 and 16×10^?2M NH₄NO₃ was prevented by soaking seeds for 4 h before sowing in a mixture of $\text{GA}{}_{\mathrm{<mtext>4</mtext><mtext>7</mtext>}}$ and kinetin+phosphate buffer, and was partially prevented by soaking them for 4 h before sowing in phosphate buffer. These treatments did not prevent inhibition of radicle emergence by 32×10^?2M NH₄NO₃, but seeds soaked in growth regulators or phosphate buffer before sowing and taken from this NH₄NO₃ solution after 7 days and washed to remove excess salt gave 45–52% germination compared with 12 % for untreated seeds. Pre-treatment of the seeds did not prevent the inhibitory effect of NH₄NO₃ on radicle extension. In field experiments seeds treated with growth regulators + phosphate buffer or phosphate buffer alone gave a higher final percentage emergence from soils given 125 kg N/ha than did untreated seeds.     

Ca storage and hypobaric storage of white peach ‘Okubo’

White peach ‘Okubo’ fruits were stored for 3 weeks at 1°C in cold storage, controlled atmosphere (CA) storage (3% CO₂ + 3% O₂ and 0% CO₂ + 3% O₂) and hypobaric storage ($\text{1}\text{7}\text{and}\text{6}\text{7}\text{atm}\text{.}$) After removal from storage, fruits were ripened at 20°C. In cold-stored fruits, low temperature injuries (flesh browning, mealy breakdown and abnormal peeling) developed. When O₂ was maintained at 3% without CO₂, the ripening rate after storage was faster than that of fruits which had been held at 20°C directly, and low temperature injuries were not controlled. Under the atmospheric conditions of 3% O₂ and 3% CO₂, ripening rate after storage was not different from that of directly ripened fruits, and injuries were almost completely controlled. In the fruits kept in hypobaric storage of $\text{1}\text{7}\text{atm}\text{.}$, the ripening rate after storage was slower than that of fruits stored in air at 1 atm. (cold storage). Mealy breakdown was reduced, but no effect was found on the flesh browning nor on the abnormal peeling. No significant differences were found between hypobaric-stored fruits of $\text{6}\text{7}\text{atm}\text{.}$ and cold-stored ones.     

Environmental and cultural effects on vegetative growth and flowering of selected “bedding” ornamentals. II. Night-break lighting and gibberellic acid applications

Weekly foliar applications of $\text{GA}{}_{\mathrm{<mtext>4</mtext><mtext>7</mtext>}}$ (GA; 25 p.p.m.) during seedling growth promoted reproductive development of both Tagetes patula and Matthiola incana whether grown in short days (8 h), or long days effected by night-breaks (NB). The NB treatment was unfavourable for flowering in Tagetes but promoted leaf growth whereas both GA and NB, favourable for early flowering and associated stem elongation in Matthiola, inhibited leaf growth. The GA applications substituted for the long-day requirement for flowering in Matthiola. These findings are coupled with those reported earlier for the effects of night temperature on vegetative growth and flowering and are discussed in relation to a possible “blue-print” for commercial horticultural practice.     

Light responses of photosynthesis and transpiration of two tomato cultivars under ambient and altered CO2 and O2

Young plants of two tomato (Lycopersicon esculentum L.) cultivars, ‘Sonatine’ and ‘F6-IVT’, were examined for whole plant photosynthesis and transpiration in a closed gas-exchange system under different light levels and a combination of high or low oxygen (21 or 1%) and high or low carbon dioxide concentrations (1850 or 550 mg m^?3). With saturating light, both cultivars showed approximately equivalent increases in photosynthesis in response to lowering the oxygen concentration, raising the carbon dioxide, or both. Under non-saturating light, ‘F6-IVT’ responded positively to lowered oxygen but CO₂ had little effect. In ‘Sonatine’, changes in O₂ as well as CO₂ gave photosynthetic enhancement under low light. Stomates responded primarily to CO₂ with little response to O₂. As a result of the stomatal behavior to light, plant water-use efficiency in the short term peaked at moderate light levels, was enhanced by low O₂, but was enhanced most by high CO₂, regardless of O₂ concentration.