Effect of temperature on growth and flowering of litchi (Litchi chinensis Sonn.) cultivars

Summary

Moderate day/night temperatures (20/15° v. 15/10°C) increased vegetative growth and reduced flowering in the seven litchi cvs Tai So, Bengal, Souey Tung, Kwai May Pink, Kwai May Red, Salathiel and Wai Chee. At higher temperatures (25/20° and 30/25°C), vegetative growth was promoted further and flowering eliminated. Temperature also influenced the type of inflorescence formed. More leaves were formed on the panicles of trees growing at 20/15° than at 15/10°C. All terminal shoots on all cultivars produced panicles at 15/10°C. The relative order for the amount of flowering at 20/15°C was: ‘Wai Chee’>‘Salathiel’>‘Kwai May Pink’>‘Tai So’>‘Bengal’>‘Souey Tung’>‘Kwai May Red’. Cultivars which were vigorous at high temperatures produced fewer panicles at 20/15°C and fewer leafless panicles at 15/10°C. Only small differences were observed in the leaf water potential and the nutrient status of the shoots at different temperatures. Vigour and flowering of the cultivars in the glasshouse generally reflected field performance in subtropical Australia (Lat. 27°S). Low vigour could be useful for selecting litchi cultivars for good fruiting in environments with warm autumns and winters.     

Acclimatisation to mannitol-induced water deficit in miniature rose (Rosa hybrida) plantlets cultivated in vitro under autotrophic conditions

Summary

Miniature rose plantlets at the flower development stage were grown photo-autotrophically on MS medium and subsequently exposed to water deficits of –0.23, –0.32, –0.40, or –0.67 MPa osmotic potential ( _s) for 14 d. The _s in the culture medium was raised by increasing the concentration of mannitol, which caused abnormal floral development in terms of the flowering percentage and the number of flowers per plantlet, as well as delayed flowering. In vitro flowering and the number of flowers per plantlet declined significantly when miniature rose plantlets were exposed to water deficit stress at –0.40 MPa or –0.67 MPa. Reductions in growth, pigment degradation, chlorophyll a fluorescence, and net photosynthetic rate (Pn) were greatest in plantlets exposed to a water deficit stress of –0.67 MPa. This was particularly evident in the case of Pn, with a decline of 73.7% compared to non-stressed control plantlets. In contrast, proline levels increased in plantlets under water deficit stress, as proline performs a key role as an osmoprotectant under such conditions. The flowering stage in miniature rose plantlets is particularly susceptible to water deficit stress, which suppresses the development of reproductive organs. Knowledge of the responses to water deficit stress at the reproductive stage may be applied to identify effective indices for the selection of genotypes with increased tolerance to water deficit in miniature rose breeding programmes.     

Effect of temperature on growth,dry matter production and starch accumulation in ten mango (Mangifera indica L.) cultivars

Summary

Ten mango cultivars of tropical and subtropical origin (Carabao, Kensington, Nam Dok Mai, Alphonso, Dashehari, Florigon, Glenn, Irwin, Haden and Sensation) were grafted onto cv. Kensington seedling rootstock and held at four day/night temperatures for 20 weeks (15/10°C, 20/15°C, 25/20°C and 30/25°C). Vegetative growth increased with increasing temperatures. All grew vegetatively at 25/20°C and 30/25°C. Cultivars which did not grow at 20/15°C were Carabao, Kensington and Dashehari. Cultivars Kensington, Nam Dok Mai, Alphonso, Florigon, Glenn, Irwin, Haden and Sensation produced flower panicles at 15/10°C. The rise in temperature increased the average number of growth flushes (in responsive cultivars) from 0.48 at 15/10°C to 3.21 at 30/25°C, and the number of leaves per growth flush (1.22 at 15/10°C to 13.63 at 30/25°C). Distribution of dry matter from new growth was mostly to the roots at the lowest temperature (95% at 15/10°C) and to the leaves (58%) at 30/25°C. The mean daily temperature for zero vegetative growth was calculated to be 15°C. Temperature and related growth activity also affected the concentration of starch in the woody tissue of rootstock trunks at the end of 20 weeks (15.9% starch at 15/10°C v. 4.8% starch at 30/25°C). ‘Irwin’ had the highest starch concentration at the two higher temperatures (twice that of any other cultivar at 30/25°C) while ‘Kensington’ the lowest starch level at 25/20°C, ca. 50% of most other cultivars.     

Regulated deficit irrigation in ‘Clementina de Nules’ citrus trees. II: Vegetative growth

Summary

An experiment on Regulated Deficit Irrigation (RDI) was performed during 1995 and 1996 in an orchard planted with drip-irrigated ‘Clementina de Nules’/Carrizo Citrange in Moncada (Valencia) Spain. Treatments consisted of a control, irrigated during the whole year at 125% ET_lys and RDI treatments where irrigation was reduced to 25% or to 50% of crop evapotranspiration measured by a weighing lysimeter (ET_lys) during one of the following periods: I) flowering and fruit set (spring); II) initial fruit enlargement phase (summer) and III) final fruit growth and maturation phases (end of summer-autumn). An additional treatment, denominated 50%-Year, was irrigated at 50% ET_lys during the whole year. The effects of RDI treatments in relation to tree water status (pre-dawn Ψ^pd and midday Ψ^md leaf water potential, as well as their integral with time) show a good relation between total shoot emergence in the different growth flushes and the stress intensity reached (Ψ^pd) (r² = 0.80). This correlation was mainly due to the number of floral shoots (r² = 0.86) and not to vegetative ones (r² = 0.22). Similar results were observed between the stress integral at pre-dawn in each period and the former sprouting variables. In all cases, correlation was better with pre-dawn leaf water potential or with pre-dawn stress integral than with those at midday. RDI during spring reduced shoot length of the first growth flush (A1) and increased fruitlet fall after restarting normal irrigation. It also produced “off-season” flowering in the second flush growth (A2) and increased shoot emergence of the third flush growth (A3) with about 10% of them being floral. Summer RDI treatments did not alter vegetative growth, and although they produced off-season flowering (A3) it was much smaller than that of autumn RDI treatments, which in addition reduced vegetative growth with respect to the control. These effects, together with those of yield and fruit quality presented elsewhere, show that summer is the more appropriate period to apply RDI in “Clementina de Nules” mandarin trees.     

Promotion of floral initiation in ‘Fuerte’ avocado by low temperature and short daylength

Potted avocado (Persea americana Mill., cv. ‘Fuerte’) plants were maintained in growth cabinets for up to 32 weeks and new growth observed for flower formation. Flowers were formed if temperatures were 20°C or below, but with 25° or 30°, even if only for 1 hour per day, flower formation was inhibited. Time to flowering was accelerated, but number of flowers reduced, if daylength was shortened from 15 h to 9 h. With low temperature and short days, full bloom was about 4 months after starting experiments. Spring flowering of cv. ‘Fuerte’ in the field could follow flower induction about 4 months previously with the onset of winter temperatures and daylengths.     

Water use and fruit yield of mango (Mangifera indica L.) grown in a subtropical Mediterranean climate

Mango (Mangifera indica L.) is one of the most important fruit crops in tropical and subtropical regions worldwide. On the coast of Granada and Malaga (SE Spain), irrigated subtropical fruit species have been introduced and cultivated on terraces with a considerable economic importance as the only European production region. The subtropical fruit production in this zone is possible with intensive irrigation on terraces, which are economically more profitable than traditional rainfed crops (almond and olive), which have been replaced or abandoned. A 2-year monitoring period was conducted using drainage lysimeters to determine the crop coefficients (Kc) and fruit yield in mango (Mangifera indica L. cv. Osteen) orchards. Also, some quality parameters such as titratable acidity, total soluble solids, and vitamin C were evaluated under these conditions. The averaged Kc values of mango trees varied within production cycle of 0.43, 0.67, and 0.63 at flowering, fruit set, and fruit growth, respectively. In this study, the fruit yield under full water requirements (100% ET_C) averaged 24.1 kg tree^?1, amounting to 21.2 kg ha^?1 mm^?1 in terms of water-use efficiency. The quality parameters of the mango fruits harvested in the study area were satisfactory. Thus, this study highlights the need to optimize the irrigation-water use according to actual mango requirements, thereby achieving more sustainable Mediterranean subtropical farming in orchard terraces.     

Effects of day and night temperature on photosynthesis,antioxidant enzyme activities,and endogenous hormones in tomato leaves during the flowering stage

To study the effects of day and night temperature difference (DIF) on tomato growth, a controlled experiment using Solanum lycopersicum L., cv. Jinguan 5 was conducted. The daily mean temperature (T_m) was maintained at 18°C and 25°C, and the DIF was set at 0°C, 6°C, and 12°C. The results indicated that chlorophyll a (Chl a) and chlorophyll b (Chl b) gradually increased as DIF rose. At 18°C T_m, the carotenoid content reached a maximum at 12°C DIF. The Chl a/Chl b, net photosynthetic rate (P_N), photosynthetic rate at irradiation saturation (P_max), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), stomatal limitation value, the maximum assimilation rate (A_max), apparent quantum efficiency (A_q), carboxylation efficiency (C_e), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), gibberellin A₃ (GA₃), and indole-3-acetic acid (IAA) were highest, while malondialdehyde (MDA) was lowest at 6°C DIF. At 25°C T_m, P_N, P_max, A_max, A_q, C_e, g_s, C_i, CAT, POD, GA₃, IAA, and zeatin reached the maximum under 6°C DIF, while SOD and MDA reached the maximum under 12°C DIF. Furthermore, the morphological index peaked at 6°C DIF under 18°C and 25°C T_m. The results suggested that 6°C DIF improved the growth and development of tomato during the flowering stage. ABBREVIATIONS: Aq – apparent quantum efficiency; Amax – the maximum assimilation rate; CAT – Catalase; Chl a(b) – chlorophyll a(b); Ca – ambient CO₂ concentration; Ce – carboxylation efficiency; Ci – intercellular CO₂ concentration; DIF – difference between day temperature (TD) and night temperature(TN); FM – fresh mass; gs – stomatal conductance; GA₃ – gibberellin A₃; IAA – indole-3-acetic acid; Ls – stomatal limitation value; MDA – malondialdehyde; Pmax – photosynthetic rate at irradiation saturation; PN – net photosynthetic rate; POD – peroxidase; ROS – reactive oxygen species; SOD – superoxidedismutase; Tm – daily mean temperature; ZT – zeatin.     

Long-day control of flowering in everbearing strawberries

Summary

Photoperiod and temperature control of flowering in a number of perpetual-flowering or everbearing strawberry cultivars of widely varying pedigree has been studied in controlled environments. Flower bud initiation in the cultivars ‘Flamenco’, ‘Ridder’, ‘Rita’ and ‘Rondo’ was significantly advanced by long-day (LD) conditions at temperatures of 15°C and 21ºC; while, at 27ºC, flowering took place under LD conditions only. Some plants of the seed-propagated F₁-hybrid ‘Elan’, raised at 21°C, also flowered under short-day (SD) conditions at 27°C, but reverted to the vegetative state after a few weeks when maintained under these conditions. When vegetative plants growing in SD at 27°C were transferred to LD conditions at the same temperature, they consistently initiated flower buds and started flowering after about 4 weeks. At such a high temperature, flowering could thus be turned on and off by switching between SD and LD conditions. This applied to all the cultivars studied. Also the cultivar ‘Everest’, which was tested only at 21°C, produced similar results. Night interruption for 2 h was effective in bringing about the LD response. At 9°C, flowering was substantially delayed, especially in ‘Flamenco’ and, at this temperature, flowering was unaffected by photoperiod. Runner formation was generally promoted by high temperature and SD conditions, but the photoperiodic effect varied between experiments. We conclude that everbearing strawberry cultivars, in general, whether of the older European-type or the modern Californian-type originating from crosses with selections of Fragaria virginiana ssp. glauca, are qualitative (obligatory) LD plants at high temperature (27°C), and quantitative LD plants at intermediate temperatures. Only at temperatures below 10°C are these cultivars day-neutral.     

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 scanning electron microscope study of flowers of avocado,litchi, macadamia and mango

Flowers of the avocado (Persea americana Mill. cultivar ‘Fuerte’), litchi (Litchi chinensis Sonn. cultivar ‘Brewster’), macadamia (Macadamia integrifolia Maiden and Betche cultivar ‘Hinde’) and mango (Mangifera indica) L. cultivar ‘Haden’) were examined using the scanning electron microscope (SEM). Micrographs of whole flowers and floral parts are presented. The SEM shows the floral structure in more detail than has been possible with light microscopy. Relationships between structure and function are discussed.     

Root shoot interactions in passionfruit (Passiflora sp.) under the influence of changing root volumes and soil temperatures

Summary

Passionfruit are grown in the tropics and subtropics where mean monthly soil temperatures at 15 cm range from about 10° to 30°C. The choice of rootstock can also influence production with most industries exploiting either the purple (Passiflora edulis f. edulis) or golden passionfruit (P. edulis tflavicarpa). We examined the relationship between shoot and root growth in purple x golden hybrid E-23 grafted onto golden passionfruit seedlings. Growth was manipulated by varying the volume of the soil available to the roots or temperature of the root zone. Shoot and root growth increased as root zone volume increased from 0.3, 1.4, 4, 12 to 24 1. Shoot weight (W_s) was correlated with root weight (W_R):W_S = 12.697 + 5.272 W_R + 0.195 W_R² (r² = 91%, P<0.001), with the plants allocating a smaller proportion of dry matter to the roots as root weight increased. Differences in shoot growth with pot volume were not due to changes in water or nutrient status. In the temperature experiment, the two critical root zone temperatures at 90% of maximum growth were about 20° and 35° C for vine extension, leaf area, node and leaf production, and 20° and 30°C for flower production. Leaf and stem dry weight were optimal between about 18° and 34°C, while maximum root growth occurred at 38°C. There was a weak relationship between shoot (W_s) and root dry weight (W_R): W_s = ?19.346 + 24.500 W_R ?1.046 W_R² (r² = 53%, .P<0.001). Apparently, variations in shoot growth at different soil temperatures cannot be explained solely by differences in root growth. Reduced growth at 10°C was associated with lower chlorophyll concentration, stomatal conductance and net CO₂ assimilation, but not lower leaf water potential. The concentration of most nutrients were lower at 10°C than at higher temperatures, but none was outside the range which would be expected to restrict growth. There appears to be a co-ordination of shoot and root growth as the soil volume available for root growth increases, whereas root temperature affects the roots and tops differently. The results of the pot volume experiment demonstrate the importance of rootstock vigour in passionfruit breeding. Productivity would be affected in cool subtropical areas with soil <20°C and in tropical areas with soil >30°C.     

Response of container-grown photinia to moisture stress

Two experiments were conducted to determine the effect of Vapor Gard (VG), an antitranspirant, and moisture stress on shoot water potential of container-grown photinia. In Experiment 1, plants sprayed with VG has less moisture stress than plants with no VG when 24.0 and 27.5 mm of net evaporation occurred prior to watering. Recovery periods for shoot water potential were within 4, 8 and 24 h for photinia stressed to 21.5, 24.0 and 27.5 mm of net evaporation, respectively. Photinia with and without VG were compared in Experiment 2. Shoot water potential and stomatal opening were measured pre-dawn daily (for 9 days) on photinia stressed to ?25 and ?35 bars pre-dawn shoot water potential before watering. Plants watered daily had a maximum pre-dawn shoot water potential of ?3 bars, and watered plants had a higher shoot water potential than stressed plants. Within 8 h after watering, plants with a pre-dawn stress of ?25 bars recovered to shoot water potentials of plants watered daily, and stomates closed regardless of VG treatment. Pre-dawn stress to ?35 bars resulted in a longer recovery period of shoot water potential (about 36 h). Stomates were closed on plants treated with VG and open on plants not treated with VG. Defoliation (25–75%) occurred on plants stressed to ?35 bars and not treated with VG.     

Diurnal and seasonal changes in the xylem water potentials of Grevillea and Myoporum plants during drought

Summary

Drought is an irregular feature of World climate and has adverse effects on ornamental plants growing in urban environments. Grevillea ‘Moonlight’ and Myoporum elipticum are attractive native Australian species that are commonly used in parks and gardens and are generally regarded as being drought-tolerant. Diurnal and seasonal water relations during a drought cycle of G. ‘Moonlight’ and M. elipticum, growing together in a non-irrigated garden bed, were monitored during a Summer (wetter)-to-Winter (dryer) transition period using a pressure chamber. G. ‘Moonlight’ generally maintained higher xylem water potentials than M. elipticum. Pre-dawn xylem water potentials in drought-affected M. elipticum dropped to around –2.5 MPa, while G. ‘Moonlight’ maintained pre-dawn xylem water potentials of around –1.0 MPa. This difference suggests that, because pre-dawn xylem water potentials reflect soil water potentials, G. ‘Moonlight’ accessed a different or additional source of soil water to M. elipticum. This study demonstrates the utility of the pressure chamber for describing the diurnal and seasonal water relations of ornamentals in a mixed planting in urban horticulture.     

Regulated deficit irrigation in `Clementina de Nules' citrus trees. I. Yield and fruit quality effects

Summary

An experiment on Regulated Deficit Irrigation (RDI) was performed during 1995 and 1996 in a ten year old, drip-irrigated `Clementina de Nules' mandarin orchard in Moncada, Spain. Treatments consisted of a control, where irrigation was applied without restriction during the whole year at 125% ET_lys and RDI treatments where irrigation was reduced to 25% or to 50% of crop evapotranspiration measured by a weighing lysimeter (ET_lys) during one of the following periods: I) flowering and fruit set (spring, 20 March to 3 July in 1995, and 1 April to 1 July in 1996); II) initial fruit enlargement phase (summer, 4 July to 7 August in 1995, and 2 to 28 July in 1996), and III) final fruit growth and maturation phases (end of summer–autumn, 8 August in 1995, and 29 July in 1996 to harvest). An additional treatment, denominated 50%–Year, was irrigated at 50% ET_lys during the whole year. The effects of the treatments on yield and fruit quality in relation to tree water status (pre-dawn (c^a) and midday (c^md) leaf water potential, and their time integral) show large differences in sensitivity to water stress according to phenological stage. The critical periods were the flowering and fruit set phases. The main treatment effects during each period were: In spring, a decline in c^a and c^md with respect to the control of only 0.1 to 0.2 MPa reduced yield by 62% and 28%, respectively for the 25% and 50% levels, due to an increased ``June drop'' and consequent fewer fruit harvested per tree. Final fruit size and quality were similar to those of the control. In summer, RDI treatments allowed water savings between 7 and 14% without affecting yield or fruit quality, providing that a threshold value of c^a–1.3 MPa is not surpassed. In autumn, for the 25% and 50% levels there was a 25 to 11% reduction of fruit size, respectively, with some external peel disorders (creasing) which reduced fruit quality, even at the lower water stress levels reached in the 50% treatment during this period (c^a 20.64 MPa and 20.83 MPa in 1995 and 1996, respectively). In treatment 50%–Year, where water application was 44% of that in the control, minimum c^a values were around 20.6 MPa and 20.8 MPa in 1995 and 1996, respectively. Tree growth was reduced in both seasons and average yield decreased by 17%. Yield loss was due to smaller, not fewer fruit. This treatment increased TSS and acids in the juice, without affecting the maturity index or creasing. However, in the current market situation, this irrigation strategy could be recommended only as a long-term one in cases of very high water prices.     

Aroma volatiles emission in relation to chilling injury in ‘Kensington Pride’ mango fruit

Summary

Mature green mango fruit (Mangifera indica L. ‘Kensington Pride’) were stored at 0, 5, 10, 15 or 20°C for 1, 3, 7, 14, 21 or 28 d to induce different levels of chilling injury (CI) and to elucidate its relationship with aroma volatile production. The fruit were removed from storage and allowed to ripen at 22 ± 1°C and CI index was assessed on fully ripe fruit. Aroma volatile compounds were estimated from the pulp of fully ripe fruit. CI index significantly increased as the storage temperature was lowered and the storage period was extended, particularly in the fruit stored at 0, 5 or 10°C. CI symptoms did not develop on fruit stored at 15 or 20°C. Fifty-six aroma volatile compounds were identified from mango fruit pulp using headspace solid phase microextraction (SPME) technique with gas chromatography (GC-FID) and GC combined with mass spectrometry (GC-MS). Among the 56 aroma volatile compounds, 25 were quantified using GC, which included monoterpenes (±-pinene, ²-pinene, myrcene, 2-carene, ±-phellandrene, 3-carene, ±-terpinene, limonene, ocimine, ³-terpinene, ±-terpinolene, and a-terpineol), sesquiterpenes (±-copaene, ±-gurjunene, trans-carophyllene, aromadendrane, ±-humulene, alloaromadendrane, ³-gurjunene, and ledene), hydrocarbon (p-cymene), esters (methyl octanoate and ethyl caprylate), aldehyde (decanal), and norisoprenoid (²-ionone). A significant reduction in total aroma volatiles, monoterpenes, sesquiterpenes, hydrocarbon, esters, aldehyde, and norisoprenoid production were observed in fruit stored at 0, 5, 10 or 15°C compared with fruit stored at 20°C. The degree of reduction in aroma volatile compounds depended on the severity of CI, induced with different storage temperatures and storage periods. In conclusion lower temperature storage induced CI in mango fruit and adversely affected the aroma volatiles production.     

Abscisic acid alleviates the deleterious effects of cold stress on ‘Sultana’ grapevine (Vitis vinifera L.) plants by improving the anti-oxidant activity and photosynthetic capacity of leaves

The effects of exogenous application of abscisic acid (ABA) on anti-oxidant enzyme activities and photosynthetic capacity in ‘Sultana’ grapevine (Vitis vinifera L.) were investigated under cold stress. When vines had an average of 15 leaves, 0 (control), 50, 100, or 200 µM ABA was sprayed to run-off on all leaves of each plant. Twenty-four hours after foliar spraying with ABA, half (n = 5) of the water-only control vines and half (n = 5) of each group of ABA-treated plants were subjected to 4°C for 12 h, followed by a recovery period of 3 d under greenhouse conditions (25°/18°C day/night). The remaining plants in each treatment group were kept at 24°C. Cold stress increased H₂O₂ and malondialdehyde (MDA) concentrations in vine leaves, whereas all foliar ABA treatments significantly reduced their levels. Chilled plants showed marked increases in their total soluble protein contents in response to each ABA treatment. ABA significantly increased the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in cold-stressed grapevine leaves. In contrast, cold stress markedly decreased the rates of leaf photosynthesis (A) and evaporation (E), stomatal conductance (g_s), and chlorophyll concentrations in leaves, but increased intercellular CO₂ concentrations (C_i) in leaves. Treatment with all concentrations of ABA resulted in lower leaf A, E, and g_s values, but higher C_i values at 24°C. However, following cold stress, ABA-treated vines showed higher leaf A, E, and g_s values, but lower C_i values compared to control vines without ABA treatment. The application of 50–200 µM ABA allowed chilled vines to recover more quickly when re-exposed to normal temperatures, enabling the vines to resume their photosynthetic capacity more efficiently following cold stress. These results showed that, by stimulating anti-oxidant enzyme systems and alleviating cold-induced stomatal limitations, ABA reduced the inhibitory effect of cold stress on the rate of CO₂ fixation in ‘Sultana’ grapevine plants.     

Effect of gibberellic acid and Vapor Gard on ripening,amylase and peroxidase activities and quality of mango fruits during storage

Post harvest application of gibberellic acid at 200 mg 1^?1, Vapor Gard (di-l-p-menthene) at 2.5% and their combination was studied on ‘Mallika’ mangoes (Mangifera indica L.) stored at ambient temperature (37 ± 2° maximum and 34 ± 2°C minimum) and at 15°C. Significant delay in the ripening of mango fruits was observed when gibberellic acid was applied with or without Vapor Gard. Gibberellic acid significantly retarded the degradation of ascorbic acid and chlorophyll in the peel, and reduced a-amylase and peroxidase activities during storage. Loss of weight decreased following treatment with Vapor Gard either alone or with gibberellic acid during storage at both ambient temperature and at 15°C. A pronounced retardation of ripening was observed when fruits were treated with gibberellic acid and Vapor Gard and stored at 15°C. The study thus suggests that mango fruits can be successfully stored for 20 d by application of gibberellic acid (200 mg 1^?1) in combination with Vapor Gard (2.5%) and stored at 15°C.     

Factors affecting the response of tulips to gibberellin

Gibberellic acid (GA₃) treatment of forced tulip crops has potential for producing faster growth to anthesis in the glasshouse, for reducing losses due to floral bud blasting, and for reducing the duration of cold storage needed to obtain satisfactory flowers. Using partly and fully cooled direct-forced tulips, cultivar ‘Apeldoorn’, several factors (relevant to the definition of GA₃ treatments) were studied. Experiments confirmed the previously recorded effects of gibberellins in tulips: GA₃ injections reduced the duration of the glasshouse period, enhanced flower survival and flower length, and reduced stem length at flowering.Following bulb storage at temperatures from ?2 to 20°C, GA₃ reduced the glasshouse period by 15–25% and increased flower length, compared to controls, irrespective of storage temperature. Stem length was also reduced by GA₃, this effect being greater following a storage temperature of 5°C or lower. When GA₃ was applied during the period of 17°C-storage which precedes cool storage, or during or after storage at 5°C, it was found that treatments during or at the end of cool storage were more effective in producing the characteristic effects of GA₃ than were pre-cooling applications. In partly cooled bulbs (but not fully cooled ones), the GA₃-induced earliness of flowering was about doubled when GA₃ injections were given repeatedly at 2-week intervals throughout storage. The responses to GA₃ injections were found to be unmodified by early-lifting and heat-treatment (for earlier forcing), by delaying the start of 5°C storage (for later forcing), by glasshouse temperature (16 and 18°C), and by shading treatments; there was little effect of bulb size.     

Some physiological changes in strawberry (Fragaria × ananassa ‘Camarosa’) plants under heat stress

Summary

The effects of heat injury induced by long exposures were evaluated in strawberry (Fragaria × ananassa ‘plants’) Camarosa in this study. Seedlings were grown in 14 × 12 cm pots using perlite for three weeks at 25/10°C day/night temperature, and watered daily by modified 1/3 Hoagland nutrient solution. Half of the plants were transferred to a growth chamber with a constant 25°C, 16/8 h (light/dark) photoperiod regime and 1200 lux light intensity for a week to acclimate the plants. Temperature was increased stepwise (5 K per 48 h) to 30, 35, 40°C and finally to 45°C. In addition to others, plants were transferred from the outside to the growth chamber, at each temperature step to impose a heat shock. Leaf relative water content (RWC, %), loss of turgidity, chlorophyll content (Spad value) and heat-stress tolerance (HTS; LT₅₀) were measured in control and stressed plants. Total soluble proteins and total DNA were extracted from the leaves following the above treatments using standard procedures and total protein contents were determined using a Bradford assay. In general, effects of gradual heat stress (GHS) and shock heat stress (SHS) on the variables studied were mostly significant, except for chlorophyll content, while the effect of temperatures was significant for all the variables. Interaction between the heat stress type and temperature treatments was not significant for leaf RWC, loss of turgidity and chlorophyll content. Data also indicated that total protein and DNA contents were changed significantly by heat stress types (GHS and SHS) and/or temperature treatments. The plants exposed to GHS exhibited a significant increase in HST compared with the plants exposed to SHS (LT₅₀ of 41.5°C and 39°C, respectively). Consequently, gradual heat stress increased HST in strawberry leaves. Increased HST may be associated with the accumulation of several heat-stable proteins in GHS plants.     

Effect of temperature on pollen germination and pollen tube growth of four cultivars of mango (Mangifera indica L.)

Summary

The effect of a constant (10, 15, 20 or 25°C) or a diurnal maximum/minimum (15/5, 20/10, 25/15 or 30/20°C) incubation temperature on in vitro pollen germination and pollen tube growth in the pistils of two poly-embryonic (‘Kensington’ and ‘Nam Dok Mai’), and two mono-embryonic (‘Irwin’ and ‘Sensation’) mango cultivars was studied. In in vitro experiments where pollen was incubated in a liquid germination medium for 24 h in darkness, little difference was found between pollen germination of mono- and poly-embryonic cultivars. Averaged over the four cultivars, 53.9% of pollen germinated at 10°C, this increased to 76.2% when the incubation temperature was increased to 15°C, thereafter up to 25°C the percentage germination remained stable but germination decreased slightly to 68.2% at 30°C. Similarly, there was no difference in percent germination between cultivars when pollen was incubated under diurnal temperature regimes. Mean pollen germination of all four cultivars was 52.3% at 15/5°C and pollen germination increased by 10% when the temperature was raised to 30/20°C. When self-pollinated flowers were incubated for 24 h on a semi-solid agar medium at 10°C, pollen tube growth of the four cultivars was retarded and no pollen tubes reached the ovaries. As the temperature was increased from 15 to 25°C, the mean number of pollen tubes in ovaries increased from 0.04 to 0.25. At 30°C, the mean number of pollen tubes that entered ovaries decreased to 0.04. After incubation under diurnal temperature regimes, the mean number of pollen tubes in ovaries of all four cultivars at 15/5°C was 0.23 and increased to 0.42 when the temperature increased to 30/20°C. At each incubation temperature, there were significant differences in pollen tube growth between cultivars, but there were no differences between the temperature response of pollen from mono- and poly-embryonic cultivars.