The influence of temperature,daylength and calendar date on cold tolerance of Rhododendron

Summary

Physical factors changing the acclimation and deacclimation processes that lead to cold (frost) tolerance and susceptibility in Rhododendron cv. Hatsurgiri are reported. Interactions between photoperiod and temperature which encouraged acclimation were studied by exposing detached leaves 0°C to –10°C, and assessing resulting injury using ion efflux and visual scoring. Combinations of short days (8 h) and exposure to 5°C resulted in the greatest cold tolerance. Exposure to long days (18 h) or 20°C reduced the cold tolerance of leaves. Application of each environmental factor, separately, increased cold tolerance compared with control tissues. When photoperiods were maintained at 12 h, exposing leaves to 5°C during the dark period enhanced cold tolerance compared with a 20°C dark period. Continuous 5°C applied during both light and dark periods encouraged greatest cold tolerance. Deacclimation from the cold tolerant state was accelerated by both higher temperature and longer photoperiods, but temperature was predominantly the more significant factor. Application of short days combined with low temperatures significantly delayed deacclimation. But even in this environment cold tolerance decreased over time, possibly through the action of endogenous annual rhythms. Cold tolerance changed with calendar time even when external environmental conditions were maintained at constant values and plant morphology was apparently unchanged.     

Changes in parameters of cell senescence in carnation flowers after cold storage

The effects of cold storage on vase life, ethylene (C₂H₄) production, and parameters of cell senescence, were measured in flowers of spray carnation (Dianthus caryophyllus L.), cultivar ‘Pink Royalette’. Storage for 6 or 12 days at 2°C led to a reduction in the subsequent vase life at 20°C. In addition, storage caused a reduction in the time between the rise in ethylene production and the end of vase life. That is, cold storage increased the sensitivity of the petal cells to endogenous C₂H₄.Normal aging of flowers for 6 days at 20°C led to decreased capacity of petals to take up [¹⁴C] sucrose, decreased activity of membrane ATPase, increased membrane microviscosity and decreased membrane phospholipid content, relative to the levels in fresh flowers. However, cold storage of flowers for 6 days at 2°C caused opposite changes in the levels of these senescence parameters (measured at constant temperature). It was concluded that cold storage does not simply lead to a slow rate of senescence, but has other effects on cell properties.     

Changes in the contents of phenolic substances,phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) accompanying chilling-injury of eggplant fruit

The mechanism of browning, which is a typical chilling-injury of eggplant fruit (Solanum melongena L.), was investigated by determining the changes of phenolic substances, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) either during storage at 1°C or after exposing fruit to low temperature for various periods.Chlorogenic acid and its isomer, the main substrates for browning, were isolated from eggplants by column and paper chromatography. R_f values and various color reactions of the above acids were compared with those of authentic chlorogenic acid.After 2 days of cold storage at 1°C, when browning was initiated, chlorogenic acid content decreased to less than half that of the initial day, rose to a maximum after 4 days, and then decreased rapidly.PAL activity increased to a peak after 2 days at 1°C, then decreased over 10 days as browning increased. TAL activity also increased after transfer from 1°C to 20°C.It is suggested that rapid turn-over of chlorogenic acid occurs in the early stage of cold storage of eggplant fruit, and development of browning is closely related to chlorogenic acid, PAL and TAL.     

Effect of intermittent warming on the reduction of chilling injury of Villa Franka lemon fruits stored at cold temperature

Storing lemon fruits at temperatures below 13°C caused chilling injury, namely physiological and chemical disorders and the development of excessive rot. However, warming the fruit for 7 days at 13°C after every 21 days in cold storage prevented chilling injury and enabled lemons to be kept in storage for six months and longer and retain marketable quality.     

The cold storage life of ‘Dashehari’ mangoes

Cold storage of ‘Dashehari’ mangoes at 7.2° to 7.9°C and relative humidity of 85 to 90 %, harvested on 2 dates after precooling, and after 2 or 4 days exposure to room temperature, revealed that lettuce-green fruits and those with light yellow colour stored successfully for 35 or 25 days respectively. Precooling increased the satisfactory storage life. Even after 2 or 4 days room-temperature storage prior to cold storage, the green fruits were in good condition for 35 days and light yellow fruits for 25 days. These fruits, after removal from cold storage, ripened to a satisfactory palatability.     

Effect of temperature manipulation during storage and ripening on firmness,extractable juice and woolliness in nectarines

‘Independence’ nectarines were stored at — 0.5°C for three or four weeks or at 3°C for four weeks or kept at room temperature for 18 h prior to storage for four weeks at -0.5°C. After cold storage, fruit from all treatments was ripened at 10°, 15°or20°C. In all treatments the percentage woolly fruit initially increased to high values and thereafter decreased with further ripening. The rate of increase and decrease in woolliness depended on the ripening temperature. A storage period of four weeks at — 0.5°C resulted more woolliness during subsequent ripening. Woolliness persisted longer after a four-week cold storage period than after a three-week one. When fruit was delayed at room temperature prior to cold storage, woolliness generally developed earlier and to a lesser extent during ripening. At all ripening temperatures initial storage at 3°C resulted in most woolliness extending over the longest period. In addition, browning of the meso- carp tissue occurred only in fruit cold stored at 3°C.-The delay period before cold storage decreased fruit firmness by 15.7 to 17.6 N. Except for fruit subjected to the delay period, the extractable juice in fruit of all treatments first decreased during ripening to low values then increased.     

Studies on keeping-quality of vegetables and fruits. III. Changes in sugar and organic acid contents accompanying the chilling-injury of eggplant fruits

The mechanism of chiiling-injury in fruits of eggplants (Solanum melongena L. cultivar ‘Hyonaga’) was investigated by determining the sugar and organic acid content during cold storage and after exposure to low temperature for various periods. Fructose, glucose and maltose were detected, and totalled more than 96% of total sugar on the initial day. Total sugar content increased to 30% higher than the initial day after 2 days of cold storage, and after that decreased gradually, while in 20° C-stored fruits it decreased sharply. Fructose, glucose and maltose increased rapidly after transfer from 1° C to 20° C. Succinic, oxalic, malic and citric acid were detected before storage. Malic and citric acid were found to be the main organic acids. The ratio of malic/citric acid in fruits stored at 1°C decreased during storage, while after storage at 20°C it increased. The ratio in fruits after transfer from 1°C to 20°C increased rapidly during the time course. The ratio of malic/citric acid ranged from 6.0 to 6.8 in healthy fruits, while it was below 5.9 or above 7.3 in chilled fruits. It is suggested that according to this ratio the degree of chilling-injury of eggplant fruits might be foreseen.     

Changes in Ripening Behaviors of 1-MCP-Treated ‘d’Anjou' Pears After Storage

Abstract

1-Methylcyclopropene (1-MCP), an ethylene action inhibitor, was applied to ‘d’Anjou' pears (Pyrus communis L.) at 20°C between 2 and 5 days after harvest. Scald of ‘d’Anjou' pears was completely controlled by 1-MCP at a concentration between 0.05 and 0.3 µl l1 after a prolonged cold storage plus 7 days of exposure to an environment with or without 500 µl l1 ethylene at a temperature of 20°C or 25°C. 1-MCP inhibited the biosyntheses of α-farnesene and its oxidative products (conjugated trienes) and thus controlled scald. However, fruit treated with the above concentrations of 1-MCP did not ripen normally in an environment with or without ethylene. Ethylene production and fruit softening of 1-MCP-treated ‘d’Anjou' pears were inhibited during 7 and 15 days at 20°C. ‘d’Anjou' fruit treated with 0.01 and 0.02 µl l¹ 1-MCP ripened normally on day 7 at 20°C after 3 months of cold storage at ? 1°C, and ripened fruit did not develop any incidence of scald. Untreated fruit developed substantial scald. After 4 months of storage or longer, both untreated fruit and fruit treated with 0.01 and 0.02 µl l 1 1-MCP developed an unacceptable incidence of scald upon ripening. Thus, use of other scald control methods may be necessary in addition to treatment with a low dosage of 1-MCP to insure both normal ripening and scald control for d'Anjou pear fruit from the Mid-Columbia district.     

Preventing cold storage disorders in nectarines

A storage experiment was aimed at preventing low temperature storage disorders in nectarine fruits, of cvs July Red and Autumn Grand. Fruit was either cooled immediately after harvest or kept at 20°C for 48 h, before transfer to controlled atmosphere (CA) conditions at 0°C. Combinations of 0, 10, 15 and 20% C02 with 8 and 16% 02 were assayed. The fruit was evaluated following cold storage, 31 days after harvest, and after four and eight days under ‘shelf conditions’ (ripening at 15-18 °C). Warming of the fruit at 20°C before cold storage prevented woolliness in the absence of elevated C02 levels but did not affect internal browning and increased reddish discoloration; further, it enhanced water loss and ripening, increasing fruit softening markedly. Conversely, high C02 delayed fruit ripening in CA storage, keeping the fruit firmer, and preventing the development of woolliness, internal browning and reddish discoloration during ripening, the best results being mostly obtained with 20% C02. 02 levels assayed did not show clear effects, but decreased 02 concentration in absence of high C02 showed some benefit in ‘July Red’. No deleterious effect of C02 concentrations even as high as 20% could be detected. Thus, even though high C02 in CA conditions showed promise for controlling disorders and preventing over-ripening, further work is needed on other cultivars, and lower 02 concentrations should be investigated before making a general recommendation.     

The influence of sucrose,ethanol and calcium nitrate on the freezing-point and long-term low-temperature storage of carnation flowers

Both tight bud and open carnation (Dianthus caryophyllus L.) flowers survived ?4°C for 5 days without injury if flowers were pulsed with 20% sucrose at 25°C for 24 hours prior to storage. Between the 8th and 10th day of storage, both stem and floral tissue froze. Flowers pulsed with 10 or 20% ethanol for 24 hours at 25°C survived ?2°C for 5 days, while those pulsed in water failed to open normally or were frozen when stored at 0°C for 5 days. Flowers stressed (wilted) for 24 hours at 25°C survived for only 5 days at ?4°C. After pulsing, tight buds were more resistant to freezing than open flowers and stem tissue was more resistant than petal tissue. However, during storage stem tissue froze before petal tissue. Using exotherm analysis, petal tissue froze at ?2.3 or ?4.7°C when first pulsed with water or sucrose and at ?3.0 and ?3.8°C after 7 days.     

Chilling induced ethylene biosynthesis in ‘Hayward’ kiwifruit following storage

‘Hayward’ kiwifruit were stored at 0, 5, 10, 15 and 20°C for 5, 12 and 17 days before rewarming to 20°C for 10 more days. Ethylene and CO₂ production, ACC, ACC synthase (ACS) and ACC oxidase (ACO) activities, flesh and core firmness, soluble solids content (SSC) and flesh colour were measured. Kiwifruit stored at 0, 5, 10 and 15°C did not ripen, produce ethylene or show increases in ACS or ACO activity. Fruit stored for 5 days at the above temperatures, then rewarmed to 20°C, did not show any change during the following 10 days. Rewarmed fruit, pre-stored at 0–10°C for 12 days, started autocatalytic ethylene production within 24 h, followed by fruit ripening. Fruit stored at 15°C for 12 days needed 72 h to start ethylene autocatalyse and did not fully ripen during 10 days at 20°C. After 17 days storage at 0–15°C kiwifruit started autocatalytic ethylene production with no delay upon exposure to 20°C. Autocatalytic ethylene production correlated with increased ACC content, and increased activities of ACS and ACO. Fruit held continuously at 20°C started autocatalytic ethylene production after 19 days, with concomitant increases in ACC content, ACS and ACO activities and ripening. Respiration increased after rewarming, concomitantly with the increase in ethylene production.We concluded that exposing kiwifruit to chilling temperatures (0–10°C) for 12 days advanced ethylene biosynthesis and ripening when compared with fruit held continuously at 20°C. The advanced ethylene biosynthesis was due to increase ACS and ACO activities immediately upon rewarming of the fruit.     

Effect of low-pressure storage on the quality of green capsicums (Capsicum annum L.)

Green capsicums (Capsicum annum L.) were stored under low pressure (4 kPa) at 10°C for 5 and 11 days with 100% RH. The results showed that the incidence of stem decay under low-pressure storage for 5 and 11 days and storage at ambient atmosphere at 20°C for 3 days was lower compared to fruits that were stored at regular atmosphere at 10°C. Fruit that had been stored at low pressure at 10°C had no symptoms of flesh rots for up to 11 days, whilst fruit which had been stored at regular atmosphere at 10°C had 6% flesh rots after 11 days storage at 10°C.There was no difference in flesh firmness and colour retention between fruits stored at low pressure and regular pressure at 10°C. Capsicums stored at low pressure had higher overall acceptability compared to fruit that were stored at regular atmosphere at 10°C. These results demonstrate the potential of low pressure storage as an effective technique to manage capsicum fruit quality, however, there was no additional benefit when fruits were stored at low pressure for more than 5 days.     

Artificial cold treatment,gibberellin application and flowering response of kohlrabi (Brassica oleracea L. var. gongylodes L.)

Juvenility, cold requirement and the effect of GA₃-application on flowering have been studied for some cultivars. If present, the juvenile phase was very short. Cold treatment for 8–12 weeks at 4 °C followed by 2 weeks at 10 °C gave flowering in all cultivars. Gibberellin sprays (250 or 500 p.p.m., 3 times) after an incomplete cold treatment promoted bolting and flowering even in the slow-bolting ‘Trero’, having the highest cold requirement.     

Effects of pre-sowing seed treatments and temperatures on tomato seed germination and seedling emergence

Sowing pre-germinated seeds with radicles 2–3 mm long reduced the time from sowing to seedling emergence to 17 days compared with 41 days in untreated seeds at soil temperatures of 10°C, and to 5 days compared with 11 days at 18°C. Sowing pre-germinated seeds also improved percentage seedling emergence and reduced the variability of times of emergence of individual seedlings. Seeds imbibed for 56 h before sowing (radicles just emerging) emerged about 3 days earlier at both 10°C and 18°C than untreated seeds. Seeds soaked in a solution containing 1.5% each of KNO₃ and K₃PO₄ for 5 days at 24°C, or in “Carbowax 20 M” for 20 days at 15°C, and then dried before sowing, gave results similar to imbibed seeds. Soaking seeds in 70% of their weight of water followed by drying for different lengths of time and for different numbers of cycles of wetting and drying did not improve germination or seedling emergence.     

Influence of Early-Season Temperature on the Growth and Branching of Newly-Grafted Apple Trees

Newly-grafted trees of apple cv Discovery on MM.106 were grown in pots at 25°C before transfer to growth rooms at 20°C; some were then subjected to 5 or 10 d at 10°C. The continuous 5-d cool period stimulated branching without reducing main shoot growth but the 10-d cool period reduced main shoot growth and did not stimulate branching. Subjecting similar plants to a night temperature of 0°C for various periods also stimulated branching but the number of cold nights and the stage of scion shoot growth influenced the magnitude of the response.     

Cold treatments enhance responsiveness to gibberellin in stock (Matthiola incana (L.) R. Br.)

Summary

Endogenous GAs have been suggested as regulators of stem elongation and flowering of cold-requiring plants. Here, the relationship between temperature conditions and responsiveness to GA₄ on stem elongation and flowering of stock (Matthiola incana) was investigated. The optimum temperature for induction of flower bud initiation was 10°C, and the minimum duration was 20 d in the late flowering cv. Banrei; the type of cold treatment effect on flowering was classified as a “direct effect”. Stem elongation was markedly promoted by cold treatment regardless of flower bud initiation. The cold treatment amplified the stem elongation response to GA₄. The GA₄ level necessary for flower bud initiation was lower in the 10°C treatment than in the 15°C treatment, and it became lower at longer durations of cold treatment. These results indicate that the cold treatments enhance responsiveness to GA₄ not only in the stem elongation process but also in the flower bud initiation process and that the development of responsiveness to GA₄ may correlate with the temperature and duration of cold treatment.     

A comparison of the response of different citrus fruit cultivars to storage temperature

A comparison was made of the response to storage temperatures (0–17°C) of grapefruit ‘Shamouti’ and ‘Valencia’ oranges, and lemon fruit. There was no chilling injury (CI) and the incidence of rot was relatively low at 12°C or higher for all cultivars. At low storage temperatures, however, pitting and subsequent rot development in grapefruit and in ‘Shamouti’ and ‘Valencia’ oranges were highest at 6°C, while in lemon the incidence of these disorders rose with the decrease in storage temperature, and was highest at 2°C. Grapefruit and ‘Shamouti’ oranges exhibited the highest susceptibility to CI, lemon showed an intermediate susceptibility, and ‘Valencia’ orange a very low one. In grapefruit, severe peel pittings that developed in cold storage were covered by mold rots during cold storage and shelf-life, but in ‘Valencia’ and particularly in ‘Shamouti’ oranges the incidence of decay during cold storage was low. During shelf-life, a pronounced CI-induced increase in the incidence of mold rots was evident. This breakdown during shelf-life may be associated with microscopic peel injuries which are formed during cold storage and covered by mold rots during shelf-life. Increased susceptibility of the cultivar to CI could be correlated with an increase in ethanol content at low temperatures.     

Physical dormancy in myrtle seed

The nature of dormancy in seeds of myrtle (Myrtus communis L.) was investigated. Scarification with cold acid or sand paper and soaking in water increased seed germination, whilst stratification, inserting the seeds in boiling water or hot acid treatment decreased the number of germinating seeds. The highest germination was obtained by treating the seeds with 100 % cold acid for 60 min or 80 % cold acid for 120 min. Hard seed coat was found to be the principal cause of poor seed germination.Scarified and non-scarified seeds were germinated for 2 weeks at 6 temperatures between 5 and 30° C, and 20° C was optimum.     

Factors affecting twin-scale propagation of narcissus

The effects of several factors on bulbil yields obtained by twin-scaling were examined in 4 narcissus cultivars (representing poeticus, trumpet and large-cup types). Bulbils were initiated on twin-scales prepared at any time of year, but grew satisfactorily only if twin-scaling was carried out between June and September. Large twin-scales initiated more bulbils, but smaller twin-scales were also effective propagules and gave high rates of multiplication and bulbils with high relative growth rates. Twin-scales cut from the outer-most scales initiated most bulbils, but more of those bulbils produced from the more central scales were recovered after 1 year; those from intermediate scales produced most and heaviest bulbils after 1 year. Partial loss of the basal plate had no effect on bulbil initiation. Optimum bulbil initiation, emergence and first-year recovery rates occurred following incubation at 15 or 20°C; at 25°C these responses were cultivar-dependent. Bulbil yield after 1 year was greater following incubation for 16 weeks compared with 12 weeks. There was little effect on bulbil yield of cold (9°C) or warm (35°C) treatments of the parent bulbs prior to twin-scaling, except for a marked reduction in the numbers of bulbils initiated when the warm treatment immediately preceded twin-scaling. When the propagules were grown on in a frost-free greenhouse (minimum, 5°C) bulbil yields were higher than from those grown either in a warm glasshouse (minimum, 18°C) or in the open; an initial cold period (5°C) given before the propagules were placed in the frost-free house also reduced yield.     

Response of the chrysanthemum to soil heating

Chrysanthemum plants were exposed to 16°C day-temperature, 11°C night-temperature, 13°C soil-temperature, to be indicated as 16/11/13°C, or to 16/11/25°C, 20/16/18°C, or 20/16/25°C, first long day, then short day, (long day = 12-h light period with 3-h night break; short day = 12-h light period) from planting to harvest in controlled environments to study the effects of soil heating on growth and flowering. There were significant, but not substantial, effects of soil heating on leaf area, percent soluble carbohydrate, flower bud diameter, days to visible bud and some other parameters. Two winter cultivars responded similarly, while 2 summer cultivars differed in flowering-response to soil heating. An experiment was also conducted using 16/11/25°C day/night/soil temperatures during long days, short days or throughout the complete growth cycle, with 16/11/13°C day/night/soil temperatures at other times. Soil heating during long days resulted in the highest quality flowers. Soil heating during short days or throughout the growth period resulted in most rapid flowering but decreased flower quality.