Seasonal impact on physiological leaf damage risk of Aechmea hybrid under greenhouse conditions

For decades bromeliad growers have to face severe leaf damage problems occurring as necrotic spots on leaves of sensitive CAM plants such as Aechmea, both in cultivation and transport. These physiological problems mainly arise during the summer period from June to September. Previous research made clear that high malic acid concentrations in the early morning generate the driving force for cellular osmotic uptake of water and can consequently induce lethal turgor pressures in sensitive Aechmea cultivars. Although it is commonly known that CAM and its related metabolites can be influenced by different environmental factors, this relationship is poorly investigated under commercial greenhouse conditions.Therefore the authors carried out four seasonal diurnal experiments with a high leaf damage sensitive Aechmea cultivar spread equally over a 1-year period. Malic acid dynamics revealed that during the critical summer period plants fail to induce malic acid consumption in the early morning causing prolonged high levels of malic acid in the leaves. Moreover, relative water content measurements did confirm that enough water is always available inside the leaves and that even slight changes in water status can be disastrous for the leaves. During the rest of the year malic acid is consumed early in the morning and is not long enough available in the leaf to cause lethal water flow. The comprehension of why this damage induction mechanism is closely related with the summer period is essential to search for possible solutions to prevent the appearance of this physiological leaf damage problem in the future.     

Seasonal changes in CO2 assimilation in leaves of five major Greek olive cultivars

Leaf CO₂ assimilation rate, stomatal conductance (g_s), internal CO₂ concentration (C_i), chlorophyll (a + b) content, specific leaf weight (SLW) and stomatal density were measured during the season, under field conditions, for five major Greek olive cultivars, ‘Koroneiki’, ‘Megaritiki’, ‘Konservolia’, ‘Lianolia Kerkiras’, and ‘Kalamon’, with different morphological and agronomic characteristics and diverse genetic background. Measurements were taken from current-season and 1-year-old leaves, and from fruiting and vegetative shoots, throughout the season, from March to November in years 2001 and 2002. CO₂ assimilation rates showed a substantial seasonal variation, similar in all cultivars, with higher values during spring and autumn and lower values during summer and late autumn. Stomatal conductance (g_s) followed similar trends to leaf CO₂ assimilation rates, increasing from March to July, following by a decrease during August and increasing again in autumn. ‘Koroneiki’ had the highest leaf CO₂ assimilation rate and g_s values (21 μmol m⁻² s⁻¹ and 0.45 mol m⁻² s⁻¹, respectively) while ‘Lianolia Kerkiras’ and ‘Kalamon’ showed the lowest leaf CO₂ assimilation rate and g_s values (13–14 μmol m⁻² s⁻¹ and 0.22 mol m⁻² s⁻¹, respectively). One-year-old leaves had significantly higher leaf CO₂ assimilation rate than current-season leaves from April to June, for all cultivars. From August and then, leaf CO₂ assimilation rate in current-season leaves was higher than in 1-year-old leaves. There were no significant differences in leaf CO₂ assimilation rate between fruiting and vegetative shoots. Total chlorophyll (a + b) content increased with leaf age in current-season leaves. In 1-year-old leaves chlorophyll content increased in spring, then started to decrease and increased slightly again late in the season. Chlorophyll content was higher in 1-year-old leaves than in current-season leaves throughout the season. Total specific leaf weight (SLW) increased throughout the season for all cultivars. Stomatal density in lower leaf surface was lowest for ‘Koroneiki’ (399 mm⁻²) and highest for ‘Megaritiki’ (550 mm⁻²). Our results showed differences in leaf CO₂ assimilation rate among the five different olive cultivars, with a diverse genetic background, ranging from 12 to 21 μmol m⁻² s⁻¹. From the five cultivars examined, ‘Koroneiki’, a drought resistant cultivar, performed better and was able to maintain higher leaf CO₂ assimilation rate, even under high air vapor pressure deficit. All cultivars had a pronounced seasonal variation in leaf CO₂ assimilation rate, affected by date of the year, depending on ambient conditions. The high temperatures and high air vapor pressure deficit occurring during summer caused a reduction in leaf CO₂ assimilation rate in all cultivars. Leaf CO₂ assimilation rate was also affected by leaf age for all cultivars, with old leaves having significantly higher leaf CO₂ assimilation rate than young leaves early in the season.     

Effect of temperature on seed and fruit development in three mango (Mangifera indica L.) cultivars

The effect of diurnal maximum/minimum (20/10 or 25/15 °C) temperatures on seed and fruit development of ‘Irwin’, ‘Kensington’ and ‘Nam Dok Mai’ mangoes (Mangifera indica L.) was studied in a controlled-environment glasshouse. Exposure to low temperatures (20/10 °C day/night) 3 days after hand pollination significantly increased the percentage of stenospermocarpic fruit (nubbins), in which embryos were aborted at some stage during early fruit development. There were significant differences between cultivars in the percentage of nubbins produced out of the total fruit set following overnight exposure to 10 °C with 21% for ‘Nam Dok Mai’, 11% for ‘Kensington’ and 3% for ‘Irwin’. At 45 days after pollination, nubbin fruits were much smaller in size and weighed ca. 50% less than normal fruits. The lower percentage of nubbin fruits in ‘Irwin’ implies a greater adaptation to cool temperatures by this cultivar during fruit set and early embryo development.     

The influence of NaCl salinity on growth,yield and fruit quality of strawberry cvs. ‘Elsanta’ and ‘Korona’

In a 2-year field study, strawberry cvs. ‘Elsanta’ and ‘Korona’ were exposed to three different levels of NaCl salinity supplied as aqueous solutions characterised by electrical conductivities of 0.3 dS/m, 2.6 dS/m, and 5.1 dS/m. Salinity in the rhizosphere reduced plant growth by up to 44% in ‘Korona’ and 90% in ‘Elsanta’. A rather distinct cultivar difference represented the reduction in leaf area per plant of 85% in the second year of experiment in ‘Elsanta’ compared to 29% in ‘Korona’. Strawberry can be regarded as a Na⁺ excluder, because Na⁺ content of both strawberry cultivars remained below 3 mg g⁻¹ dry mass at all salinity levels. Cl⁻ content increased considerably, up to 70 mg g⁻¹ dry mass in ‘Korona’ and 80 mg g⁻¹ dry mass in ‘Elsanta’ plants. ‘Korona’ retained most of its Cl⁻ in roots and crowns, whereas in ‘Elsanta’ the maximum was detected in petioles. ‘Korona’ was able to accumulate up to 33% higher Cl⁻ content in the roots than ‘Elsanta’. Macronutrient deficiency due to NaCl salinity was not observed and in comparison to ‘Elsanta’, higher Cl⁻ content in roots of ‘Korona’ did not coincide with an impairment of macronutrient uptake. Salinity stress reduced fruit yield by up to 27% in ‘Korona’ and 64% in ‘Elsanta’. Fruit quality, characterised as taste, aroma, and texture by a consumer-type panel, decreased by more than 24% in ‘Elsanta’, but in ‘Korona’ differences were insignificant. Total soluble solids (Brix) and the ratio Brix/TA (TA, titratable acid) decreased significantly by about 20% in ‘Korona’ and 35% in ‘Elsanta’. To summarise, the ability of ‘Korona’ to retain Cl⁻ in the root system more effectively than ‘Elsanta’ resulted not only in a 41% lower leaf Cl⁻ content at the highest salinity level and a better growth under NaCl stress, but also in a relatively higher fruit yield and fruit quality.     

Video evaluation of ethylene sensitivity after anthesis in carnation (Dianthus caryophyllus L.) flowers

Differences in ethylene sensitivity among carnation (Dianthus caryophyllus L.) cultivars were evaluated using a time-lapse video recording system. Measurement of time to petal inrolling of ‘White Sim’, ‘Nora’, ‘Chinera’, and line 64-54 flowers subjected to a range of 1–20 μl l⁻¹ ethylene showed that 10 μl l⁻¹ was the optimum concentration for sensitivity evaluation with our video system. With this system we found clear differences in ethylene sensitivity among 10 cultivars and one line. ‘Candy’, ‘Pallas’, ‘Chinera’, and line 64-54 had lower ethylene sensitivities than the other seven cultivars. Line 64-54 had the longest ethylene response time (20.6 h to start of petal inrolling). Video monitoring is a simple and accurate way of evaluating ethylene sensitivity. We have also used the system to study changes in the ethylene sensitivity of carnation flowers after anthesis. We were able to detect a shift in responsiveness to ethylene that was impossible to detect by previous methods. In the Sim-type carnation cultivars tested (‘White Sim’, ‘Scania’, ‘U Conn Sim’, and ‘Nora’), ethylene sensitivity after anthesis decreased significantly with age in both early-cut and late-cut flowers. These results clearly showed that decline of ethylene sensitivity is caused by the increasing physiological age of flowers. Ethylene sensitivity after anthesis decreased with age in normal Sim-type carnations in the same way as in long-vase-life variants such as ‘Sandrosa’.     

Subject Index

Prohexadione-calcium (ProCa) is a gibberellin biosynthesis inhibitor with limited persistence and low toxicity that has recently been registered as a shoot growth retardant for apples in North America (Apogee^®) and Europe (Regalis^®). We investigated the response of six different pear cultivars (‘Rosemarie’, ‘Forelle’, ‘Packham's Triumph’, ‘Flamingo’, ‘Early Bon Chretien’ and ‘Golden Russet Bosc’) to ProCa in the Western Cape, South Africa, over the period 1999–2003. ProCa treatments ranging from 50 to 250 mg l⁻¹ were applied between one and three times per season and were compared with girdling and control treatments. ProCa application reduced shoot growth in all of the cultivars. ‘Forelle’, was least responsive and showed a reduction in 2002/2003 but not 2001/2002. ‘Rosemarie’, ‘Flamingo’, ‘Packham's Triumph’ and ‘Golden Russet Bosc’ were most responsive, with shoot growth being reduced by up to 50% of the control for the latter two cultivars. The response to number of applications and ProCa concentration was not consistent across cultivars. ‘Early Bon Chretien’, for example, only responded to high ProCa concentration, whereas ‘Rosemarie’ was very responsive at the lowest ProCa concentration. ProCa application improved fruit set but decreased final fruit size in some of the cultivars, particularly in ‘Rosemarie’. It also caused a decrease in return bloom in ‘Forelle’ and ‘Packham's Triumph’. The response of different cultivars to girdling, in terms of shoot growth and fruit set was highly variable. Girdling tended to increase final fruit size and return bloom. ProCa shows potential as a shoot growth retardant for the pear cultivars investigated, but the response of reduced fruit size in some cultivars requires mitigation. Future research on combined girdling and ProCa treatments may be instructive.     

A comparative study of chlorophyll loss and its related mechanism during fruit maturation in the pericarp of fast- and slow-degreening litchi pericarp

Changes in the levels of chlorophyll a and b and their derivatives, and chlorophyllase activities were compared in the pericarp of ‘Feizixiao’ (slow-degreening) and ‘Nuomici’ (fast-degreening) litchis (Litchi chinensis Sonn.). Cluster bagging and growth regulators were used to regulate the degreening process of ‘Feizixiao’. HPLC analysis revealed the presence of chlorophyllide a, pheophorbide a and pheophytin a as chlorophyll derivatives in litchi pericarp. Loss of chlorophylls in ‘Feizixiao’ pericarp was slower than that in ‘Nuomici’ pericarp. The concentrations of chlorophyll a and b in the pericarp of ‘Feizixiao’ were significantly higher than those in ‘Nuomici’ during fruit maturation, whereas the chlorophyll derivatives in the former were noticeably lower than in the latter. Chlorophyllase activity increased as chlorophylls diminished. Chlorophyllase activity peaked around the colour-break in ‘Nuomici’, being much higher than that in ‘Feizixiao’. Both cluster bagging and treatment with abscisic acid (ABA, 200 mg l⁻¹) or jasmonic acid (50 mg l⁻¹) significantly decreased the chlorophyll content and increased the chlorophyllase activity and the anthocyanin level. In fruit treated with 6-benzyl aminopurine (6-BA, 100 mg l⁻¹) the degradation of chlorophylls was delayed, with concomitant decrease of chlorophyllase activity and anthocyanin level. These results imply that chlorophyllase is the crucial factor in the regulation of the chlorophyll loss in the pericarp.     

Inheritance and expression of fruit texture melting,non-melting and stony hard in peach

Fruit ethylene production and flesh firmness were measured in F₁ and F₂ offsprings from a cross of a non-melting cultivar ‘Nishiki’ and a stony hard cultivar ‘Yumyeong’ of peach (Prunus persicaBatsch). Fruits from genotypes that showed no natural ethylene production were treated with 1000 ppm ethylene and subsequent flesh softening was observed. Genotypes of melting and non-melting in stony hard fruits could be distinguished by the degree of softening following exogenous ethylene treatment. The stony hard trait was inherited independently of the melting flesh/non-melting flesh trait and was epistatic to this trait.     

Effects of IAA and BA on development of globular,heart- and torpedo-stage embryos from cell suspensions of three grape genotypes

In order to initiate cell and embryo suspensions, embryogenic calluses derived on NN solid medium with 2,4-D and BA from petioles of in vitro grown plants of three interspecific grapevine hybrids were cultured in three versions of liquid NN medium: (1) without growth regulators, (2) 0.1 mg l⁻¹ IAA and (3) 0.5 mg l⁻¹ BA. Cell and embryo suspensions were incubated two and three times in these versions of liquid media in various combinations. Incubating suspensions two times in hormone-free media and/or with 0.1 mg l⁻¹ IAA led to formation of globular embryos in the three cultivars studied and small numbers of heart-stage embryos in ‘Podarok Magaracha’ and ‘Intervitis Magaracha’. Numerous heart-stage embryos developed in ‘Intervitis Magaracha’ and ‘Podarok Magaracha’ when the suspensions had been initiated in medium with 0.5 mg l⁻¹ BA, and in ‘Bianca’ this was achieved after two incubations in the above medium. Torpedo-stage embryos were formed after subculturing heart-stage embryo suspensions in medium with 0.1 mg l⁻¹ IAA in all study cultivars. If only small numbers of embryos of a certain developmental heart- or torpedo- stage were formed, such cell and embryo suspensions need to be repeatedly subcultured in liquid medium with specific growth regulators to enable this process.     

Effects of cold storage on postharvest leaf and flower quality of potted Oriental-, Asiatic- and LA-hybrid lily cultivars

The effects of cold storage of mature potted plants on postharvest leaf and flower quality were investigated in several cultivars of three major groups (Oriental, Asiatic and LA) of hybrid lilies (Lilium spp.). Mature plants were stored in darkness at 3 °C for 2 weeks before placing them in a postharvest evaluation room (22 °C) and were compared with plants moved directly to the evaluation room. The efficacy of GA₄₊₇ plus benzyladenine (BA) treatments (applied just before cold storage) for preventing cold-induced postharvest disorders in each cultivar was also evaluated. In all cultivars, cold storage caused several adverse effects on postharvest quality, including accelerated leaf yellowing or browning, bud abortion and reduced flower or inflorescence longevity. Leaf abscission was observed only in Oriental-hybrids. Treatment with GA₄₊₇ plus BA significantly reduced these disorders and improved the overall postharvest quality after cold storage. While different cultivars differed greatly in their sensitivity to cold storage, all the cultivars benefited from GA₄₊₇ plus BA treatment. Experiments indicated that GA₄₊₇ plus BA treatments could be applied as early as 2 weeks before the mature bud stage without compromising the positive effects.     

The use of native turf mixtures to approach sustainable lawn in urban landscapes

Native grasses are excellent candidate species for manipulation to produce dwarf and turf type varieties as well as for producing cultivars with higher attractiveness and requiring less maintenance to be used as a turf grass in arid and semi-arid regions of the world. This investigation was conducted to explore visual qualities of native grasses and their mixtures compared to commercial turf. The field experiment was set out in a split-plot in time based on a randomized experimental design with three replications. We used two native monoculture accessions, perennial ryegrass (Lolium perenne L. ‘Yarand’) and (Lolium perenne L. ‘Shadegan’), Native low-variety Mixture (NM1): consisting of 50% Lolium multiflorum ‘Shadegan’? 50% Festuca spp. ‘Shadegan’, Native high-variety Mixture (NM2): consisting of 55% Lolium perenne L. ‘Yarand’? 35% Lolium perenne L. ‘Shadegan’? 5% L. multiflorum ‘Shadegan’ and 5% Festuca spp. ‘Shadegan’ and compared this with one commercial turf mixture that is commonly used in landscaping. Results indicated the effects of seasons and turf grass types and their interaction had significant effects on most variables including quality, season color, leaf texture, density, quality after clipping (p < 0.01). The visual quality measurements indicated the superiority of L. perenne ‘Shadegan’ over other native monoculture and polyculture and its ablility to compete with the commercial turf. The native turf mixture of NM2 showed several good characteristics. L. perenne ‘Yarand’ had statistically the lowest score for visual appeal as compared with the other turf types. This research suggests that the use of native grass species of L. perenne ‘Shadegan’ is worth investigating for better performance of the native landscape.     

Comparison of growth,leaf water relations and gas exchange of Cistus albidus and C. monspeliensis plants irrigated with water of different NaCl salinity levels

Four-month-old potted Cistus albidus and Cistus monspeliensis plants growing in a greenhouse were submitted to saline stress from 9 August to 2 December, using irrigation water containing 0, 70, and 140 mM NaCl. C. monspeliensis plants are more tolerant to saline irrigation water than C. albidus plants, mainly due to their capacity to resist stress with a lower plant biomass and canopy area; furthermore, they showed no leaf necrosis symptoms. Under saline stress conditions the main growth limiting factor in both species was photosynthesis. Both Cistus species responded to saline stress by developing avoidance and tolerance mechanisms. The avoidance mechanisms took place at a morphological and physiological level. Morphologically, the reduction in the canopy area can be considered a mechanisms for regulating water loss via transpiration. Treated C. monspeliensis plants showed a greater capacity to absorb water and were able to conserve it more efficiently than C. albidus plants. Tolerance mechanisms included Na⁺ and Cl⁻ inclusion and osmotic adjustment. However, the reaction of each species to osmotic adjustment was different, because in C. monspeliensis plants the osmotic adjustment was unable to prevent a decrease in leaf turgor. The curvilinear relationship between P_n and g_l observed in C. monspeliensis plants indicated stomatal limitation of photosynthesis below a leaf conductance of about 160 mmol m⁻² s⁻¹. In C. albidus plants, a linear relationship between photosynthesis and leaf conductance rather a curvilinear model was significant, indicating limitation of the photosynthetic capacity.     

Somatic embryogenesis and plant recovery from callus of ‘Nabali’ Olive (Olea europea L.)

Regeneration via somatic embryogenesis from callus was studied in ‘Nabali’ olive (Olea europea L.). Among different explant sources (leaf blades, leaf petioles, hypocotyls of germinated seeds and roots of germinated seeds), roots gave the highest (46%) callus induction. Somatic embryogenesis was induced from root callus on embryogenesis induction medium (EIM) containing 5.0 μM 2,4-D, 0.5 μM kinetin and 5.0 μM NAA in darkness. Embryo regeneration was studied by transferring the callus from EIM to embryogenesis expression medium (EEM) containing different concentrations (0.0, 5.0, 10.0 and 15.0 μM) of 2-isopentenyladenine (2iP), BA, thiadiazuron (TDZ), zeatin or kinetin. Among the tested concentrations, 2iP at 10.0 μM outperformed the other growth regulators. 2,4-D at 5.0 μM in the EIM was satisfactory for embryogenesis induction. Sucrose at 0.2 M evoked higher embryogenesis than any other concentration of fructose and glucose in EIM, while sorbitol and mannitol at 0.1, 0.2 or 0.3 M reduced embryogenesis significantly and inhibited it totally at 0.4 M. Somatic embryos were rooted by transferring them to hormone-free medium (HFM). About 85% of embryos converted to rooted plantlets, 5% showed secondary embryogenesis and 10% were not developed and died. Rooted plantlets gave 95% survival when acclimatized ex vitro. Acclimatized plantlets developed into whole plants in the greenhouse and they were phenotypically similar.     

Differential tolerance to iron deficiency of citrus rootstocks grown in nutrient solution

We studied the effects of Fe deficiency on physiological parameters of citrus rootstocks grown in nutrient solution. Three 4-week old rootstocks (‘Troyer’ citrange – Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf., Citrus taiwanica Tan. and Shim., and ‘Swingle’ citrumelo – Poncirus trifoliata (L.) Raf. × Citrus paradisi Macf.) were grown in nutrient solutions with 0, 5, 10, 15 and 20 μmol Fe dm⁻³. Calcium carbonate (1 g dm⁻³) was added to all solutions to mimic the natural conditions in calcareous soils. For each rootstock, shoot length, number of leaves, and root and shoot dry weights were measured at the end of experiment. Chlorophyll concentration was estimated using a portable SPAD-502 meter calibrated for each rootstock. The amount of nutrients (P, K, Mg, Ca, Fe, Zn, Mn, and Cu) was determined in shoots. Chlorophyll fluorescence parameters (F₀: basal fluorescence; F_m: maximum fluorescence; F_v = F_m − F₀: variable fluorescence) were measured with a portable fluorimeter. ‘Troyer’ citrange rootstock was the most tolerant to Fe deficiency. These plants grew more and accumulated more chlorophyll and nutrients than the others in the presence of low levels of Fe (10 μmol Fe dm⁻³). ‘Swingle’ citrumelo plants needed 20 μmol Fe dm⁻³ in the nutrient solution to secure adequate growth. ‘Taiwanica’ orange rootstock had an intermediate behaviour, but could be distinguished from ‘Troyer’ citrange based on fluorescence parameters, since there was a variation in the basal fluorescence in the former, whereas in ‘Troyer’ citrange the basal fluorescence was not affected by the supply of Fe.     

Methyl jasmonate and CMN-pyrazole applied alone and in combination can cause mature orange abscission

Methyl jasmonate (MJ) and CMN-pyrazole alone and in combination were applied to ‘Hamlin’ and ‘Valencia’ orange trees (Citrus sinensis (L.) Osbeck) in seven separate experiments in the 1998/1999 and 1999/2000 growing seasons to induce abscission of mature fruit for mechanical harvesting. MJ alone significantly reduced fruit detachment force (FDF) of ‘Hamlin’ oranges at concentrations of 10 mM and higher. However, MJ at 20 and 100 mM caused significant defoliation. For ‘Hamlin’ oranges, the most effective treatments were those combining 10 mM MJ and 50 mg l⁻¹ CMN-pyrazole, and 20 mM MJ and 25 mg l⁻¹ CMN-pyrazole. ‘Valencia’ oranges did not respond to 10 mM MJ treatments alone or in combination with CMN-pyrazole, and required MJ at 20 mM in combination with CMN-pyrazole to loosen this late-maturing variety to below 50 N, but excessive defoliation occurred.     

Quality assessment of three warm-season turfgrasses growing in different substrate depths on shallow green roof systems

In an effort to increase the accessibility and functionality of shallow green roof systems, the ability of warm-season grasses to provide acceptable growth needs to be further investigated. In the current study, which was conducted during 2011 and 2012, three warm-season grasses (hybrid bermudagrass, Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy ‘MiniVerde’; seashore paspalum, Paspalum vaginatum Swartz ‘Platinum TE’ and zoysiagrass, Zoysia japonica Steud. ‘Zenith’) were established in outdoor lysimeters. The lysimeters were equipped with all necessary green roof layers placed below a coarse-textured substrate that comprised pumice, thermally treated attapulgite clay, peat, compost and zeolite. Half of the lysimeters had a substrate depth of 15 cm, while the other half had a substrate depth of 7.5 cm. Irrigation was applied at crop evapotranspiration (ET_c). Measurements included determination of substrate moisture content, green turf cover (GTC) and leaf stomatal resistance. Significant differences were observed in the values of GTC among the three turfgrass species and the two substrate depths. Zoysiagrass exhibited the best adaptation at the lower depths of shallow green roof systems. At 15 cm substrate depth, zoysiagrass managed to sustain green coverage for the two study periods. In addition, it was the only turfgrass species that managed to perform well at the substrate depth of 7.5 cm. Seashore paspalum exhibited limited green cover at both substrate depths, while hybrid bermudagrass could provide acceptable green coverage only at 15 cm substrate depth.     

Variability between silver thiosulfate and 1-naphthaleneacetic acid applications in prolonging bract longevity of potted bougainvillea

Potted bougainvillea ‘Purple Flower’ and ‘Taipei Red’ in four different stages of bract development were sprayed with STS (0.1, 0.5 mM) or NAA (25, 50 ppm) and were moved to low-light indoor conditions after treatment. The experiment was conducted twice, and the results showed that 0.5 mM STS and NAA (25, 50 ppm) could significantly prolong the longevity of bracts at certain stages in both cultivars. Treatment with 0.1 mM STS, however, had no effect on bract longevity of ‘Taipei Red’ at any stage. The prolonging effect of STS was more obvious in early bract stages and decreased as the bract stage increased, whereas NAA applications at later bract stages produced better results on prolonging bract longevity. The ethylene production rates of bracts in these two cultivars were higher in early stages and gradually decreased with bract growth. We propose that this phenomenon is related to the variability between STS and NAA in prolonging bract longevity of bougainvillea.     

Determination of background pyruvic acid concentrations in onions,Allium species,and other vegetables

Background pyruvic acid concentration is a critical factor to determine onion pungency but greatly different values have been reported. This study was initiated to measure accurate background pyruvic acid levels in onion cultivars, other Allium species, and non-Allium vegetables using an HPLC method. A microwaving time of 2 min per 100 g was sufficient to deactivate alliinase and further degradation of pyruvic acid was not observed up to 6 min. Five percent trichloro acetic acid was suitable for both fresh and frozen tissues, while 80% ethanol did not stop the alliinase activity completely. The background pyruvic acid concentrations in various onion cultivars were less than 0.34 μmol ml⁻¹, while garlic and onion sprouts were 0.84–0.95 μmol ml⁻¹. Non-Allium vegetable also showed very low levels (0.09–0.34 μmol ml⁻¹) of pyruvic acid in the microwaved tissues. This study confirmed that background pyruvic acid levels in onion were minimal and could be disregarded in a routine analysis. Previous reports of high levels of the background pyruvic acid may need to be reviewed for accuracy.     

Application of ammonium thiosulfate for blossom thinning in apples

The efficacy of ammonium thiosulfate (ATS) in blossom thinning was investigated as a function of concentration, drying time and flower development stage at the time of treatment. In 2-year-old crabapple trees, flower damage caused by ATS, applied at a concentration of 10 g/l, increased as the drying time of the ATS spray increased. Approximately 40% of flowers were damaged when the ATS spray dried in 30 min, significantly less than the 80% damage observed when the drying time was 71 min. Application of ATS at 2% resulted in high levels of flower damage regardless of drying time. Fully developed open flowers were more susceptible to ATS damage than closed flowers. Ethylene does not appear to have a major role in mediating the thinning activity of ATS, as the levels of flower and leaf damage were unaffected by the use of an ethylene inhibitor. In ‘Jonagold’ apples, ATS at either 5 or 10% provided excellent thinning but was phytotoxic unless washed off the trees. The effects of drying time and flower development stage on ATS activity can be countered by applying ATS at a concentration of 5% at petal fall then washing the tree with water within 1 h of application to avoid excessive thinning and leaf damage.     

Prohexadione-calcium affects growth and flowering of petunia and impatiens grown under photoselective films

The response of petunia (Petunia x hybrida Vilm.-Andr. ‘Countdown Burgundy’) and impatiens (Impatiens wallerana Hook ‘Accent Orange Tempo’) to Prohexadione-calcium was evaluated under a clear and a far-red light absorbing greenhouse (A_FR) film to investigate the dosage effect of Prohexadione-Ca and to determine if it can overcome the flowering delay under FR deficient greenhouse environments. Prohexadione-Ca reduced stem elongation of petunia and impatiens under A_FR and clear films when applied 3 weeks after germination. Late applications were less effective. In both crops, main stem length decreased in a quadratic pattern as the concentration of Prohexadione-Ca increased. Under both films, 50–100 mg l⁻¹ Prohexadione-Ca resulted in ≈30% shorter petunia plants. Greater concentrations (500 and 1000 mg l⁻¹) resulted in excessively short plants (over 70%). Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis of petunia by 8 and 3 days under the clear film and the A_FR film, respectively during less inductive photoperiods but had no effect during inductive photoperiods. In impatiens, Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis over 10 days under clear or A_FR film. Greater concentrations (200 and 300 mg l⁻¹) inhibited flowering of impatiens. Prohexadione-Ca treatments significantly affected flower color development. Untreated petunia plants had dark burgundy flowers. Prohexadione-Ca treatment increased L*, a*, and C* values and decreased hue angle indicating that the flowers were faded. Flowers of untreated impatiens plants were bright orange color. Prohexadione-Ca at 100 mg l⁻¹ increased L* value and decreased a*, b*, and C* values indicating that significant petal fading had occurred. Flowers of treated plants were nearly white under both films. Although effective in height control, loss of color would be a major limitation to the use of Prohexadione-Ca on flowering crops.