Genetic improvement of vase life of carnation flowers by crossing and selection

We used conventional cross-breeding techniques to develop many carnation lines with long vase life and either low ethylene production or low ethylene sensitivity. Two cycles of selection and crossing to improve vase life led to a 3.6-day increase in mean vase life. All 39 selected lines had significantly longer vase life than the control cultivar, ‘White Sim’. In particular, second-generation lines 63-3, 63-12, 66-15, and 63-41 had a mean vase life of more than 15 days without chemical treatment. Measurements of ethylene production indicated that flowers of all second-generation selected lines had a greatly reduced capacity to produce ethylene. We screened three lines (515-10, 64-13, and 64-54) with low ethylene sensitivity. Evaluation by exposure to ethylene at high concentration showed that 64-13 and 64-54 were less sensitive to ethylene than ‘Chinera’, which is known for it low sensitivity. The vase life of these low-sensitivity lines was about twice that of ‘White Sim’. The extended vase life of selected lines was related to low ethylene production at flower senescence rather than to degree of ethylene sensitivity in young flowers. Ethylene sensitivity decreased with the age of the flower in many selected lines. The results clearly show that vase life of carnation flowers can be extended by crossing and selection.     

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.     

Selection of ethylene-resistant carnations (Dianthus caryophyllus L.) by video recording system and their response to ethylene

We used conventional cross-breeding techniques to develop a carnation with low ethylene sensitivity. A time-lapse video recording system for evaluating ethylene sensitivity of flowers, developed in our earlier study, proved useful for this breeding. We selected 10 new ethylene-resistant lines, in addition to the previously selected line 64–54. Lines 902–48a, 234–43S, and 234–36S showed extremely low ethylene sensitivity. The response time to 10 μL L⁻¹ ethylene of these three lines exceeded 50 h in two independent experiments (2004 and 2005), whereas that of three sensitive control cultivars (‘White Sim’, ‘Excerea’, and ‘Scania’) was 6.2–8.0 h. The mean vase life of the ethylene-resistant lines ranged from 7.6 to 12.7 days (1.4–2.3 times that of ‘White Sim’). The application of ethylene to carnation flowers induced autocatalytic ethylene production in both petals and gynoecia of 9 of the 11 ethylene-resistant lines without petal wilting, indicating that the autocatalytic ethylene production was regulated independently of the petal wilting reaction. This result further suggests that these lines have normal ethylene receptors and produce ethylene autocatalytically, but their petal wilting reaction stops at a point beyond the receptor. Two lines (118–64S and 120–69S) showed extremely low ethylene production at flower senescence and very low autocatalytic ethylene production from petals and gynoecia.     

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 putrescine application on fruit set in ‘Housui’ Japanese pear (Pyrus pyrifolia Nakai)

In Japan, artificial pollination is practiced to improve fruit set as well as fruit size and to obtain perfect round shapes in ‘Housui’ (S₃S₅) Japanese pear and most commercial cultivars that present gametophytic self-incompatibility. The period of artificial pollination application is limited by environmental conditions and the availability of a labor force. The present study aimed to determine if pre-pollination applications of putrescine (1.0 and 0.01 mM) positively affect fruit set in ‘Housui’ after hand-pollination. During 2002 and 2003, fruit set in late pollinated flowers increased with pre-pollination putrescine applications and concentrations of 1.0 mM had a better effect than 0.01 mM. In vitro pollination tests revealed that higher pollen germination was present in the stigmas of flowers sprayed with 1.0 mM of putrescine compared to the controls. Putrescine application did not affect post-pollination ethylene production in the styles. Moreover, in the styles of non-treated flowers, an increment of putrescine content and ethylene production after pollination was found, suggesting post-pollination responses and confirming the lack of antagonism between polyamines and ethylene at least during this process.     

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.     

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.     

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.     

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.     

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.     

Foliar treatment of Mn deficient ‘Washington navel’ orange trees with two Mn sources

The objective of this study was the comparison of the effect of two Mn sources (MnSO₄·H₂O, MnEDTA) which were applied at various concentrations (0, 200, 400, 800, and 1200 mg Mn l⁻¹) to the leaves of ‘Washington navel’ orange trees in order to correct Mn deficiency.One hundred and seventy days after the foliar application of Mn solutions, the mean Mn concentrations in the leaves treated with MnSO₄·H₂O (200, 400, 800 or 1200 mg Mn l⁻¹) or MnEDTA (400, 800 or 1200 mg Mn l⁻¹) were significantly higher than those of the control leaves. Manganese sulfate (MnSO₄·H₂O) was more effective than MnEDTA regarding the improvement of the leaf Mn concentrations of the trees, when applied at equal Mn concentrations. Finally, the leaf Mn concentrations were in the sufficiency range (>25 mg kg⁻¹ d.w.), only after the application of 800 or 1200 mg Mn l⁻¹ as MnSO₄·H₂O.     

In vitro induction of tetraploid ginger (Zingiber officinale Roscoe) and its pollen fertility and germinability

In vitro induction of tetraploid ginger (Zingiber officinale Roscoe) and its pollen fertility and germinability were investigated. The growth of shoot tip cultures on agar MS medium containing 2.0 mg l⁻¹ BA was greater than that of similar cultures in liquid MS medium with the same BA concentration. In liquid medium, the combinations of 0.5, 1.0, or 2.0 mg l⁻¹ BA with 0.05 mg l⁻¹ NAA tended to enhance the growth of the cultures. The efficiency of tetraploid induction was assessed by treating shoot tip explants on agar or in liquid MS medium containing 2.0 mg l⁻¹ BA, 0.05 mg l⁻¹ NAA, and 0.2% (w/v) colchicine for 4, 8, 12, and 14 days. The total number of tetraploids induced on solid medium was 18, but only five in liquid medium. On both media, the colchicine treatment for 8 days gave the maximum level of tetraploid induction. Therefore, it was found that the treatment of shoot tip explants on agar medium containing 2.0 mg l⁻¹ BA, 0.05 mg l⁻¹ NAA, and 0.2% (w/v) colchicine for 8 days was the most efficient way of inducing tetraploid ginger. Induced tetraploid strains, ‘4× Kintoki’, ‘4× Sanshu’, and ‘4× Philippine cebu 1’, had higher pollen fertility and germinability than the diploid counterparts, i.e., in the diploid strains, pollen fertility ranged from 0.3 to 6.2% and the germination rate from 0.0 to 0.1%, while in the tetraploid strains, pollen fertility ranged from 27.4 to 74.2% and the germination rate from 4.8 to 12.9%.     

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 phytohormones on in vitro shoot multiplication and rooting of lime Citrus aurantifolia (Christm.) Swing

Multiple shoots were produced from node explants of lime (Citrus aurantifolia (Christm.) Swing) on MS medium supplemented with 6-benzylaminopurine (BAP), 6-furfurylaminopurine (kinetin) and α-naphthaleneacetic acid (NAA). The highest number of shoots, nine shoots per node, were produced on a medium containing 2 mg l⁻¹ BAP (8.8 μM), 1 mg l⁻¹ kinetin (4.6 μM) and 1 mg l⁻¹ NAA (5.4 μM). Depending on the concentration of BAP and kinetin, NAA either inhibited, stimulated or did not affect shoot multiplication, which also depended on the cytokinin level. Maximum shoot length was obtained from treatments containing 0.5 mg l⁻¹ BAP (2.2 μM) combined with 1 mg l⁻¹ kinetin (4.6 μM) and 0.5 mg l⁻¹ NAA (2.7 μM). The largest leaves of resultant shoots were produced on a medium containing 0.5 mg l⁻¹ each of kinetin (2.3 μM) and NAA (2.7 μM). Transferring in vitro shoots to rooting media containing indole-3-butyric acid (IBA) and NAA produced complete plantlets. The highest rooting percentage was obtained on a medium containing either 1 mg l⁻¹ NAA (5.4 μM) alone or 0.5 mg l⁻¹ NAA (2.7 μM) combined with 2 mg l⁻¹ IBA (9.6 μM), whereas the highest number of roots were produced on a treatment containing both 2 mg l⁻¹ NAA (10.8 μM) and 2 mg l⁻¹ IBA (9.6 μM). Roots elongated most on treatments containing 0.5 mg l⁻¹ of either NAA (2.7 μM) or IBA (2.4 μM). Shoot growth associated with the rooting phase was the highest in response to 2 mg l⁻¹ IBA (9.6 μM) or 0.5 mg l⁻¹ NAA (2.7 μM). Plantlets that survived acclimatization, 82%, exhibited normal growth in soil under greenhouse conditions.     

Factors affecting the shoot multiplication of Persian walnut (Juglans regia L.)

A number of experiments were conducted to identify suitable procedure for in vitro shoot multiplication of Persian walnut (Juglans regia L.). Three different nutrient media (DKW, MS and WPM) and three different gelling agents (Phytagel, Difco Bacto agar and a mixture of Phytagel and Difco Bacto agar) were studied in the first experiment. Driver and Kuniyuki walnut (DKW) medium solidified with 2.2 g l⁻¹ Phytagel was found optimum. Performance of explants was better on DKW medium than on MS and WPM. The DKW and MS media were not significantly different from each other, but both of them were significantly better than WPM, which was a very poor medium for this species. Phytagel alone was significantly better than Difco Bacto agar or Phytagel combined with Difco Bacto agar. In another experiment different concentrations of BA were studied. Medium containing 1.0 mg l⁻¹ BA and 0.01 mg l⁻¹ IBA was the best, although medium containing 0.6 and 0.8 mg l⁻¹ BA were also successful, and utilisation of 0.4 mg l⁻¹ BA and 0.01 mg l⁻¹ IBA was optimum for shoot elongation. Application of different kinds of auxins (IAA, IBA and NAA at 0.01 or 0.1 mg l⁻¹) with 1.0 mg l⁻¹ BA were also studied. Media containing IBA were significantly better than media containing IAA for shoot fresh weight, but neither of them was significantly different from media containing NAA. Application of 0.01 mg l⁻¹ or 0.1 mg l⁻¹ auxin, with 1.0 mg l⁻¹ BA, was not significantly different for shoot multiplication of Persian walnut. The morphology of shoots on media containing 0.01 mg l⁻¹ IBA was the best.     

GA4+7 plus benzyladenine reduce foliar chlorosis of Lilium longiflorum

The effectiveness of two commercial formulations of gibberellin (GA) and benzyladenine (BA) for reducing foliar chlorosis on Easter lily (Lilium longiflorum Thunb.) was compared. On a per liter basis, plants were sprayed with 0, 100, 200, or 400 mg (BA equivalent) of Accel (GA₄₊₇:BA of 1:10) or Promalin (GA₄₊₇:BA of 1:1) when the crop leaf area index (LAI)=3. One group of plants was sprayed with 100 mg of Accel or Promalin (BA equivalent) per liter twice: once at LAI=3 and again 3 weeks later. Plants were harvested when the largest flower bud on each plant measured 13 cm in length, stored for 0 or 3 weeks at 2.5°C in the dark, and then moved into a post-harvest evaluation room at 21°C, where foliar chlorosis was monitored for 3 weeks. Senescence of some lower leaves on plants in every treatment was evident at harvest, and incidence of senescence increased during the 21 days of post-harvest evaluation. Cold storage increased the number of leaves senescing during the subsequent evaluation period. Application of Promalin or Accel significantly reduced leaf senescence compared to that of untreated plants. At harvest, 21% of the leaves on untreated plants were senescent, while plants treated with Promalin or Accel averaged 3 or 9% senescent leaves, respectively. Following 7 days of post-harvest evaluation, Promalin was more effective in preventing chlorosis than Accel at the 400 mg l⁻¹ (BA equivalent) level. Following 14 or 21 days of post-harvest evaluation, Promalin was more effective than Accel for the 100 mg l⁻¹ 2× and 400 mg l⁻¹ (BA equivalent) treatments.Plants in all Promalin and Accel treatments were taller than untreated plants 1 week after sprays were applied. At harvest, plants sprayed with Promalin were between 6 and 14 cm taller than untreated plants, but those treated with Accel were the same height as untreated plants.Neither Promalin nor Accel influenced the occurrence of malformed or aborted flowers in this study. However, cold storage significantly increased the number of plants with aborted buds and malformed flowers. Unstored plants averaged 0.16 aborted buds and 0.02 malformed flowers each, while those stored 3 weeks averaged 0.51 aborted buds and 0.18 malformed flowers each.     

Effect of air humidity variation on powdery mildew and keeping quality of cut roses

Vase life, flower opening and development of mildew were studied in six cut rose cultivars grown at daily periods of 0, 6, 12, 18 and 24 h at 90% and 75% relative air humidity (RH) was determined. Air humidities corresponded to vapour pressure deficits (vpd) of 220 and 550 Pa, respectively. Treatment with drought stress was included at the constant high RH treatment. On increasing RH from constant 75% to constant 90%, vase life decreased by between 15% and 70% in the different cultivars. High RH for up to 18 h generally had only a minor effect on vase life, but there was a significant deterioration between 18 and 24 h (continuous). On increasing the daily period of 90% RH from 0 to 12 h, the percentage of flowers opening during vase life in one of the cultivars decreased; a further increase to 18 and 24 h significantly reduced flower opening in five of the six cultivars. As a mean of all cultivars, 71% and 27% of the flowers opened when grown at 75% and 90% RH, respectively. The development of mildew was much greater at 12 h 90% RH combined with 12 h 75% RH compared with all other treatments. Constant 90% RH eliminated all mildew development, while at constant 75% RH, only minor infections were observed. Drought stress at constant 90% RH increased the vase life of five cultivars and stimulated the flowers to open in three; no mildew development was observed in any of the cultivars.     

Prohexadione–Ca inhibits vegetative growth of ‘Smoothee Golden Delicious’ apple trees

Experiments to test the effectiveness of prohexadione–Ca as a growth inhibitor in apple trees have been carried out for 3 years in the Middle Ebro Valley (Spain). Also, effects on fruit quality and flower initiation were evaluated. The application of 100–400 mg l⁻¹ of prohexadione–Ca between 12 and 30 days after full bloom (DAFB) to ‘Smoothee Golden Delicious’/M9 apple trees resulted in the inhibition of shoot growth, the effect increasing with concentration, and a greater inhibition was obtained when the trees were first sprayed 12–20 DAFB. A second spray was usually needed to avoid a regrowth of the shoots. The effectiveness of the second application was related to the concentration applied and the date of the first spray. The relative increase in trunk-cross-sectional area was not affected by the growth inhibitor. No negative effects on yield and fruit quality were found except for a reduction of soluble solid content. Flower initiation in the following year was not affected. Concentrations of 100–200 mg l⁻¹ applied shortly after full bloom should be recommended, bearing in mind that a second application might be necessary 6–8 weeks later.     

Double-phase in vitro culture using sorbitol increases shoot proliferation and reduces hyperhydricity in Japanese pear

This study aimed to improve in vitro shoot proliferation efficiency without inducing hyperhydricity in Japanese pear. The shoot number increased at 2.5–10.0 mg l⁻¹ benzyladenine (BA), while shoot fresh mass increased at 1.0 and 2.5 mg l⁻¹ BA. Different macroelement formulation did not affect shoot proliferation, but adding activated charcoal (AC) to the medium inhibited markedly the production of axillary shoots and biomass and many shoots were hyperhydric. Different carbon sources (CS) significantly increased the shoot number and fresh mass, with the best results for shoot proliferation at 20–30 g l⁻¹ sorbitol. With gelling agents, the shoot number increased at 0.4 and 0.6% agar and 0.3% gellan gum, while fresh mass increased at 0.4% agar. The hyperhydric explants were more than 30% at 0.4–0.6% agar and at any concentration of gellan gum. The improved culture (woody plant (WP) supplemented with 20 g l⁻¹ sorbitol, 0.1 mg l⁻¹ 3-indolyl-butyric acid (IBA), 2.5 mg l⁻¹ BA and 0.8% agar) and double-phase culture (the same medium using a double-phase liquid-gelling agent solidified culture system) produced a higher number of axillary shoots than the conventional culture (1/2MS supplemented with 0.1 mg l⁻¹ IBA, 1.0 mg l⁻¹ BA, 30 g l⁻¹ sucrose and 0.8% agar), moreover, double-phase culture had a higher fresh mass than the other cultures.     

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.