Multiplication and distribution of iris severe mosaic virus in secondarily-infected iris bulbs after stress induced by heat and wounding

In freshly-lifted iris bulbs infected with iris severe mosaic virus (ISMV), virus was not always detected in the basal plate and rarely in bulb scale tissue. After exposing the bulbs to stress (wounding or high-temperature treatment) the sensitivity of virus detection was enhanced. The improved detection of viral antigen after local stress (wounding) coincided with an increase of viral RNA synthesis. When general stress (high-temperature treatment) was applied, the virus could be reliably detected in the basal plate, and usually in vascular bundles and surrounding tissue. Virus was detected in the upper part of the bulb scale when such tissues were detached from the basal plate. Thus, virus must have been present in the scales in localised spots, albeit at a very low concentration, and multiplication is likely to be the main factor involved in the improved sensitivity of viral detection. The distribution of ISMV in the bulb after local or general stress treatment is discussed.     

Influence of temperature,ethylene and cyanide on the occurrence of alternative respiration in mitochondria from iris bulbs

Mitochondria, isolated from iris (Iris hollandica cv. Ideal) bulbs that have been treated for early flowering with high temperatures (14 days at 35°C followed by 3 days at 40°C) or with ethylene (10–500 ppm), show an induction of alternative respiratory capacity and a rise in state III respiration. Mitochondria from untreated bulbs (stored at 30°C) do not have an alternative pathway capacity and state III respiration is low. Induction of the alternative respiration by ethylene is maximal after 24 h, while induction by high temperature (> 36°C) is much slower. In the temperature range from 36–40°C, the extent of the induced alternative respiratory capacity increases with higher temperatures. A temperature of 42°C is lethal within 5 days. Bulbs stored at 30°C and 35°C before 40°C treatment reach the same values for alternative respiratory capacity. A treatment of the bulbs with 2.2 mM HCN (30°C) leads to an induction of alternative respiration concomitant with a decrease in state III respiration, after a lag time of 2–3 days. A treatment of 5 days with 2.2 mM HCN or longer is lethal.     

Effects of anaerobiosis on ethylene production, respiration and flowering in iris bulbs

Ethylene production of iris bulbs (Iris hollandica cv. Ideal) was very low. When stored at 30°C, production was 12–20 pmol C₂H₄ (kg fresh weight)^?1 h^?1. Higher temperatures (35°C, 40°C) enhanced the ethylene production; a treatment with 40°C for ca 7 days caused a 3 times higher ethylene production than at 30°. During anaerobic storage (in 100% N₂) ethylene production was equal to that of control bulbs. When after a 7 day period of anaerobiosis the N₂ was replaced by air, a burstlike ethylene production was observed. Twenty-four h after the replacement, ethylene production was equal to control values again. The effects of this production of ethylene on mitochondrial respiration and flowering were investigated. When mitochondria were isolated immediately after the anaerobic treatment (before the enhanced ethylene production) alternative pathway capacity was not detectable, a situation also occurring in control bulbs. When mitochondria were isolated 24 h after the end of the anaerobiosis (after the ethylene burst) uninhibited respiration did not change significantly, but a capacity of the alternative pathway was observed. The increase in alternative pathway capacity after anaerobiosis was partly inhibited by 2,5-norbornadiene (NBD), an ethylene antagonist. Fermentation occurred during anaerobiosis: ethanol concentrations increased during the treatment and decreased when air was supplied. When bulbs were exposed to ethanol vapour the alternative pathway was induced but only when very high ethanol levels in the bulbs were reached. The amount of ethanol accumulated in the bulbs during a 7 day anaerobic treatment was far too low to explain the observed induction of alternative pathway capacity. Flowering percentages were enhanced after a 24 h treatment with ethylene and after a 7 day anaerobic treatment. NBD significantly inhibited the effect of exogenous ethylene and of anaerobiosis on flowering. Ethanol was not able to induce flowering. The burst-like production of ethylene after anaerobiosis probably is responsible for the effects on respiration and flowering.     

Endogenous levels of abscisic Acid and decanoic Acid in dutch iris bulbs and the influence of abscisic Acid and decanoic Acid on iris meristems cultured in vitro

Abscisic acid (ABA) and decanoic acid inhibited shoot elongation and floral development of Dutch iris (Iris hollandica Hoog. cv Ideal) meristems cultured in vitro. No synergism with respect to inhibition of leaf growth between ABA and decanoic acid was observed. With monthly harvest dates, from July 10, 1981 to October 10, 1981, there was a progressive decrease in endogenous level of free ABA in `Ideal' iris bulbs. Bulbs subjected to a full set of the usual preplanting storage conditions flowered, on average, 46 days after planting versus 194 days after planting for bulbs planted directly after harvest. ABA levels at harvest were 4- to 5-fold those after the preplanting storage treatment. In general, ABA levels did not correlate well with the length of time from planting until flowering of iris bulbs. Endogenous decanoic acid levels did not follow any pattern with respect to harvest date or postharvest treatment. After the postharvest high temperature treatment, there was about a 3-fold increase in nonscale decanoic acid concentration. Decanoic acid levels, in nonscale tissue, remained high after each of the other postharvest treatments. It is concluded that there is no good evidence to support the contention that either ABA or decanoic acid is directly involved in iris bulb dormancy.     

Exogenous GA<Subscript>3</Subscript> overcomes bud deterioration in tulip (<Emphasis Type="Italic">Tulipa gesneriana</Emphasis> L.) bulbs during dry storage by promoting endogenous IAA activity in the internodes

Endogenous free IAA was examined with an immunohistochemical method for its involvement in the reduction of bud deterioration after GA₃ was injected into the bulbs. We found that tulip bulbs stored at 20°C constantly developed severe bud deterioration, whereas the symptoms of deterioration was lighter in the bulbs with GA₃ injection and not observed in the bulbs with 4°C treatment. 73% success in overcoming bud deterioration was achieved in 20°C with GA₃ treatment after 8 weeks of bulb storage, and the success rate was 7% after 12 weeks of storage. IAA was detected in the parenchyma cells in the internodes of the shoot after the bulbs were stored at 4°C or at 20°C with GA₃ injection for 4 weeks, but little was detected in the bulbs stored at 20°C constantly. Moreover, a weak IAA signal was present in between the cells of the internodes irrespective of bulb treatment. After planting, the bulbs that had been treated differently exhibited different flowering ability. The bulbs stored at 4°C for 4, 8 and 12 weeks attained high flowering percentage, which was lower in the 20°C with GA₃ treatment and lowest in the 20°C treatment. It may be concluded that GA₃ injection decreases bud deterioration of tulip bulbs during dry storage at 20°C by promoting the endogenous IAA in the internodes.     

The effect of temperature on the rate of sprout growth and development within stored onion bulbs

In order to understand better the effects of storage temperature on the time to visible sprouting in stored onions, sprout growth was measured by regularly dissecting samples from bulbs stored at 1, 10, 15 or 25°C for 243 days. The dry-weight of the shoot or sprout within stored onion bulbs increased exponentially with time. The rate of increase of sprout dry weight, as well as the rate of leaf initiation by the shoot apex was faster at 17° than at 10 or 25°C, and almost zero at 1°C. The rate of loss of dry weight from storage tissue was similar at 17°C and 25°C but slower at 10°C and slower still at 1°C.     

The influence of temperature on weight loss from stored onion bulbs due to desiccation, respiration and sprouting

When onion bulbs were stored for 9 months at 2, 7.5, 15 or 25 °C and 70% r.h., the losses due to desiccation increased with temperature but less than 20 % was due to respiration at any of the storage temperatures. Respiration rates of onion bulbs transferred from 2 to 25 °C were higher from February onwards than those of bulbs stored continuously at 25 °C. Conversely, bulbs transferred from 25 to 2 °C respired less from February onwards than those kept at 2 °C. Sprouting, at the final assessment in June, was highest at 15 and 7.5 °C and lowest at 2 °C. Total weight loss was above 45 % in all the storage treatments except at 2 °C (12%). Storage at 7.5 °C is suitable until March but long-term storage until June requires low temperatures.     

The Effect of Storage Temperature on Shoot Growth, Flowering, and Carbohydrate Metabolism in Tulip Bulbs

Dry bulbs of the cvs. ‘Apeldoorn’ and ‘Paul Richter’ at stage G of flower development were stored at 5° or 21°C for 2, 4, 6, 8, 10, 12, and 14 weeks, respectively before being planted and forced at 18°C. Samples from each treatment were taken for carbohydrate analysis. The low temperature treatment (5°C) was necessary to obtain satisfactory shoot growth and flowering after planting. The rate of shoot growth and the percentage of flowering bulbs increased with increasing duration of the 5°C treatment. Time of flowering was also precipitated. 12–14 weeks of low temperature treatment seemed optimal. High temperature (21°C), or a short period at 5°C (2–6 weeks), resulted in many non-flowering bulbs, and a very slow shoot elongation when flowering occurred. In the latter case the tips or large areas of the perianths became white, the red pigmentation being prevented. Paper chromatographic analysis of oligosaccharides revealed a substantially increased content of sucrose and fructosyl sucrose (DP ≤ 5) during the first 2–4 weeks of cooling. At the end of 12 weeks at 5°C, the content of oligosaccharides decreased. The increase in the oligosaccharide content was accompanied by a corresponding starch decrease. High temperature storage (21°) led to comparatively slight changes in the sucrose and fructosyl sucrose content of the bulbs. The significance of carbohydrate metabolism in relation to shoot elongation and flowering is discussed.     

Long term lily scale bulblet storage: effects of temperature and storage in polyethylene bags

Collections of lily genotypes are usually maintained by yearly planting, harvesting and storage of the bulbs. To facilitate this maintenance, a storage method has been developed for a collection of lily genotypes, including Asiatic hybrids, Oriental hybrids, Lilium longiflorum and L. henryi. Scale bulblets were stored either dry, sealed air-tight in polyethylene bags, or in moist vermiculite in open polyethylene bags for a period of 2 yr. The decrease in mass, sprouting proportion and ion leakage or sprouting proportion alone were determined for treatments carried out at -2°C, °C and 17°C. Sealing scale bulblets in polyethylene bags at -2°C resulted in the smallest decrease in mass, the least ion leakage and the highest sprouting proportion after 2 yr of storage.     

Effect of octanoic acid on ethylene-mediated flower induction in Dutch iris

Treatment of Dutch iris (Iris × hollandica Hoog. cv. Sapphire Beauty) bulbs with ethylene prior to precooling stimulated flowering in bulbs of various sizes. In large sized bulbs exposure to ethylene followed by precooling resulted in 100% flowering over a five months period after planting. Flowering in control bulbs which were not treated with ethylene prior to precooling was limited to 67% during the same five months period. In medium sized bulbs flowering in the ethylene treatment was 90% compared to 75% in the control. However, the biggest stimulation of flowering by ethylene was found in small sized bulbs (from 16 to 56%). Application of octanoic acid for a short time period prior to exposure to ethylene stimulated flowering in all bulb sizes. After five months the final percentage flowering in large and medium sized bulbs of the octanoic acid plus ethylene treatment did not differ from that of the ethylene only treatment. However, the initial rate of flowering was higher in the former treatment. In small bulbs the percentage flowering was much higher in the octanoic acid plus ethylene treatment than in the ethylene only treatment. The results of this study indicate that, just as in certain flowers, fruit and seeds, treatment with octanoic acid stimulates ethylene sensitivity in Dutch iris bulbs. The sensitivity of untreated bulbs to ethylene was highest in large bulbs and lowest in small bulbs. This correlated well with the endogenous octanoic acid content of the bulbs. Octanoic acid levels were highest in large bulbs and lowest in small Bulbs. It appears that the endogenous levels of octanoic acid in the bulbs is determined prior to the onset of dormancy.     

The effect of low temperature and GA3 treatments on dormancy breaking and activity of antioxidant enzymes in Fritillaria meleagris bulblets cultured in vitro

We investigated the effect of low temperature and gibberellic acid (GA₃) treatment on dormancy in Fritillaria meleagris L. bulbs. Also, we studied the effect of dormancy breaking on the antioxidant enzymes activity. To overcome dormancy, bulbs require a period (4–8 weeks) of exposure to low temperature. Bulbs regenerated in vitro were grown in the dark on medium without growth regulators at the standard (24 °C) or at low temperatures (4 and 15 °C) for 4, 6, 8 and 10 weeks. Bulbs were collected after 3, 4 and 5 weeks of cooling at 4 °C. To investigate the influence of GA₃ on dormancy, bulbs were treated for 24 h with GA₃ solutions with 1, 2 and 3 mg l^?1 concentrations. During the period of growth of bulbs at 4 °C, regeneration of bulbs was very weak, while at 15 °C the number of regenerated bulbs increased significantly. Improved bulb sprouting was achieved by a short treatment with gibberellin. Low temperature also represents a kind of oxidative stress for the plant. The activity of superoxide dismutase, catalase (CAT) and peroxidase (POX) in bulbs of F. meleagris L. grown in vitro and ex vitro increased with decreasing temperature in contrast to glutathione reductase. POX showed generally lower activity than CAT which indicates that major role in the breaking dormancy and preparing bulbs for sprouting have catalases.     

Physiological Analysis of Flower Formation in Wedgwood Iris

A series of experiments is described in which buds and scalesof iris bulbs were implanted in nutrient media and subjectedto varying temperature treatments, in an attempt to analysethe effect of different endogenous growth factors and of gibberellicacid on flower formation. In isolated scales incubated at 13°C for one to three weeks much of a heat-stable flower-inducingcompound and a small quantity of a second growth factor is produced.At 25.5° C no such substances are formed. It is shown thatat different times during a prolonged lowtemperature treatmentof iris bulbs, different growth factors are formed which activatesuccessive stages in the differentiation of the flower primordium.At 25.5° C the production and activity of the factor responsiblefor the transition to the reproductive stage are inhibited.Probably not inhibited at this temperature are differentiationprocesses in the reproductive primordium controlled by otherfactors with gibberellin-like characters.     

Effects of delaying fungicide treatment of wounded potatoes on the incidence of Fusarium dry rot in store

Potato tubers artificially inoculated with Fusarium solani var. coeruleum or F. sulphureum 3 months after harvest were uniformly wounded and held at 5, 10 or 15°C for up to 21 days before immersion in fungicide suspensions. Holding tubers for 14 days at 15°C (curing conditions) or at 5°C did not alter the incidence of dry rot subsequently developing on tubers stored at 10°C, and holding tubers for up to 21 days at 15°C slightly increased disease caused by both pathogens. Thiabendazole, imazalil and prochloraz applied to tubers immediately after wounding almost completely prevented dry rot. Treatment after 3 days was less effective and the amount of disease increased with further delay; fungicides were more effective on tubers held at 5°C than at 10 or 15°C before treatment and storage, and efficacy of the fungicide was decreased by increasing the amount of inoculum on tubers. Wounds became less susceptible to infection by F. solani var. coeruleum and F. sulphureum when tubers were held at 15°C before inoculation, and the incidence of rots was decreased by 70–80% by delaying inoculation for 7 days. Treating tubers with dichlorophen immediately after wounding slightly increased the disease. The effects of fungicide treatment, curing conditions and wound healing are discussed.     

The effects of storage condition on starch metabolism and regeneration potentials of twin-scales and inflorescence stem explants of <Emphasis Type="Italic">Narcissus tazetta</Emphasis>

Summary The natural propagation rate of Narcissus is very slow. In vitro micropropagation of Narcissus is more efficient than conventional propagation for rapidly building up aseptic stocks of varieties, especially for the establishment of new cvs. and the production of pathogen-free stock material. In the present study, Narcissus tazetta cv. ‘Ziva’ bulbs were used as the source of mother plants. The bulbs were kept at 30°C in a dark chamber until the start of the experiments. Prior to explant preparation, the bulbs were subjected to a cold treatment at 15°C in the dark for 6 wk to break dormancy. Twin-scales and inflorescence stem discs were isolated from aseptic bulb parts and were used as the initial explants. The polar orientation affected the regeneration of the inflorescence stem. Storage duration at 30°C followed by cold treatment were found to affect starch levels, adenosine diphosphate glucose pyrophosphorylase (AGPase) activities, and regeneration potentials. Starch levels were reduced significantly during a 10 mo. storage period at 30°C in both twin-scales and inflorescence stem disc explants. Regeneration was followed by an efficient acclimatization system with 98–99% survival. More than 500 highly uniform young bulbs were propagated from one mother bulb in a 12 mo. period.     

Evidence that Tuber Respiration is the Pacemaker of Physiological Aging in Seed Potatoes (Solanum tuberosum L.)

Storage temperatures greater than 4 °C (that is, heat-unit accumulation) increase respiration and accelerate physiological aging of seed tubers. The degree of apical dominance is a good indicator of physiological age (PAGE). As seed age advances, apical dominance decreases, resulting in more stems, greater tuber set, and shifts in tuber size distribution. Herein we provide evidence that tuber respiration rate may constitute the “pacemaker” of aging. Tubers exposed to a brief high-temperature age-priming treatment initially in storage, followed by holding at 4 °C for the remainder of a 190–200-day storage period, maintained a higher basal metabolic (respiration) rate throughout storage compared with tubers stored the entire season at 4 °C. Tubers thus “remembered” the age-priming treatment as reflected by their elevated respiration rate. Moreover, reducing the respiration rate of age-primed seed by subsequently storing it at 3.5 % O₂ (4 °C) until planting significantly attenuated the effects of the aging treatment on apical dominance, tuber set, and size distribution. The effect of the age-priming treatment on the magnitude of the respiratory response was the same whether given at the beginning or toward the end of storage. However, moving the age-priming treatment progressively later in the storage season effectively decreased its impact on plant growth and development. These results underscore the importance of time in the aging process. Exposure of seed to a high-temperature age-priming treatment at the beginning or end of storage elevated respiration (the pacemaker) to the same extent; however, the timing of these treatments resulted in vastly different physiological ages. The longer the respiration rate of tubers remains at an elevated level, the greater their PAGE at planting. Thus, an accurate but impractical measure of PAGE may be the respiratory output from vine kill to subsequent planting. Respiration appears to be the pacemaker of PAGE and production, and storage conditions that affect respiration may “set the clock speed” that will ultimately determine the PAGE at planting.     

Effects of delaying fungicide treatment on the incidence of gangrene in stored potato tubers

Potato titbers infested with Phoma exigua var. foveata were uniformly wounded and sprayed or dipped in fungicide suspensions either immediately or after periods of up to 21 days' storage at 5, 10, 15 or 20 °C. Tubers were then stored at 5 °C and gangrene assessed after 12 wk. Incidence of gangrene on untreated tubers was progressively decreased by increasing the length of storage at 15 or 20° (curing) but was not affected by 3 days' storage at any temperature. Fungicide treatment immediately after wounding gave best control of the disease; treatment after 3 days' delay was less effective and after 14 or 21 days was usually ineffective. Gangrene was decreased by fungicides more on tubers stored for 3 or 7 days at 5 °C than at higher temperatures. Control of gangrene by curing or fungicides diminished when the amount of inoculum on tubers was increased. Increasing the amount of fungicide applied improved control and fungicides were more effective in decreasing gangrene on cut and crush wounds than on cut wounds. At the arbitrary concentrations used in these experiments imazalil gave better disease control than thiabendazole, prochloraz, carbendazim plus quinolin 8-ol or triadimefon.     

Characteristic Stimulation by Ethylene of Respiration in Dutch Iris Bulbs

The low steady-state basic respiration of iris bulbs (Iris bollandica cv.‘Wedgwood') at 30°C can be enhanced by ethylene. When ethylene is administered continuously a lag period of 4 hours is followed by an increase in the rate of respiration showing two peaks, one after 24 hours and the other after 3 to 4 days. Thereafter, the respiration rate decreases gradually, notwithstanding the presence of ethylene. Concentrations of less than 0.05 microlitre ethylene per litre have no effect, and the maximum effect is observed at concentrations of 3 microlitre per litre and higher. Between 0.2 and 2 microlitre ethylene per litre the peak values of the first maximum are linearly proportional to the logarithm of the ethylene concentration applied. The characteristics of the respiratory response in iris bulbs are probably similar to those described for potato tubers and non-climacteric fruits.     

The effect of drought stress and temperature on spread of barley yellow dwarf virus (BYDV)

1 The effect of drought stress and temperature on the dispersal of wingless aphids Rhopalosiphum padi (L.) and the pattern of spread of BYDV (barley yellow dwarf virus) within wheat plants in controlled environment chambers was quantified. Combinations of three different drought stress levels, unstressed, moderate and high stress level, and three different temperatures, 5 ± 1 °C, 10 ± 1 °C, and 15 ± 1 °C, were investigated. 2 With increased temperature there was an increase in the mean distance of visited plants from the point of release and in the number of plants visited and infected with BYDV. Drought stress had no effect on mean distance moved by aphids at any temperature or on plants infected with virus at 10 °C and 5 °C. When plants were drought stressed, the numbers of plants visited and infected were greater at 15 °C than at 10 °C and 5 °C. 3 A greater proportion of plants visited by aphids was infected with BYDV when plants were stressed than when not stressed. At 15 °C a greater proportion of these plants was infected than at lower temperatures. There was no difference between treatments in the numbers of aphids present at the end of the experiment. 4 It is concluded that drought stress and temperature are of considerable importance in virus spread.     

Respiration of mitochondria isolated from tulip bulbs stored at 5 and 17°C

For the production of good quality flowers, tulip ( Tulipus gesneriana L.) bulbs need a period of low temperature. In cultivar Apeldoom a treatment of 12 weeks at 5 C can be used. In the bulb scales the respiratory metabolism has to adjust to this low temperature. Mitochondria isolated from the bulb scales are able to use succinate. NADH and pyruvate as respiratory substrates. Respiratory characteristics of these mitochondria changed after transfer of the bulbs to 5°C and the adaptation was complete within 2 weeks. Both state 3 respiration and respiratory control increased. Alternative pathway capacity was constitutively present at both 5°C and 17°C: it was low and substrate dependent at both temperatures. During the following weeks of the treatment no significant changes took place. However, when bulbs were transferred to 17°C after storage at 5°C. various responses could be demonstrated. In bulbs only cooled for a short period no readjustment to this higher temperature occurred. In bulbs stored for longer periods the change depended on the duration of the 5°C treatment. The nature of the re-adaptation is discussed     

Biological activity of Friend spleen focus-forming virus after cold storage

Two stocks of Friend spleen focus-forming virus (SFFV) were prepared, one in saline and the other in Eagle's medium with 2% fetal calf serum, and the effects of different freezing, storage and thawing temperatures were determined for the recovery of infectious virus from each diluent. Once frozen, virus maintained its titer at ?70 and at ?170 °C for up to 13 weeks, while it lost titer at ?13 °C more rapidly if it had been prepared in saline than in medium. However, during the freezing process lower ambient temperatures (?70 and ?170 °C) gave lower virus yields than a higher temperature (?13 °C) did. Similarly, rapid thawing (in a 37 °C water bath) was less efficient than slow thawing (in 4 or 20 °C air) for the recovery of infectious SFFV, This study illustrates the importance, for efficient recovery of leukemogenic activity from stored murine leukemia virus stocks, of the temperature used for freezing or thawing, as well as for storage.