The influence of apical dominance on the in vitro multiplication of the rhizome of Alstroemeria

The effects of mechanical and chemical methods of removing or reducing apical dominance on the multiplication of Alstroemeria cultivars grown in vitro were assessed. Subculture of rhizome explants without aerial shoot or rhizome apices and of rhizome explants divided into single internodes with or without aerial shoots, significantly enhanced rhizome multiplication. Subculture of rhizome explants with only the aerial shoot or rhizome apices removed produced no significant differences. Addition of the plant growth regulators T1BA, thidiazuron, NAA, GA3 and paclobutrazol to culture media, with or without BAP, did not significantly change the numbers of lateral rhizomes, shoots or roots produced. Paclobutrazol, however, extensively changed explant morphology.     

Effect of pruning and plant spacing on the growth of cherry rootstocks and their influence on stem water potential of sweet cherry trees

Summary

The aims of this work are to describe the effects of pruning and planting density on growth and water relations of ungrafted and grafted sweet cherry trees. A trial with cherry rootstocks ‘Prunus avium’, ‘CAB 11E’, ‘Maxma 14’, ‘Gisela 5’ and ‘Edabriz’ was begun in 1997. Pruning severities were applied to the rootstocks (0, 30, 60 and 90% of the vegetative growth was removed corresponding to P1, P2, P3 and P4 treatments, respectively) after planting to two plant spacings (S1 = 0.25 × 1.0 m and S2= 0.45 × 1.5 m). Canopy, root growth and leaf water potential (ψ_leaf) were quantified throughout the growing season. Pruning significantly affected root length and root weight of the rootstocks. Uncut plants (P1) showed a heavier and expanded root biomass (231 g and 108 m) than the intensively pruned plants (P4) (187 g and 75 m). The greater root biomass was obtained with the spacing/pruning combination, S1/P1 (285 g), and the smaller with S1/P4 (180 g) and S2/P4 (176 g). ψ_leaf varied significantly between the rootstocks and plant spacing but not with pruning. ‘Maxma 14’ and ‘P. avium’ attained the lowest values of midday ψ_leaf, –2.28 and –2.04 MPa, but the highest values of predawn ψ_leaf, –0.29 and –0.25 MPa, respectively. Generally, with high density (S1), the rootstocks exhibited lower predawn and midday ψ_leaf. In 1998, cultivars ‘Burlat’, ‘Summit’ and ‘Van’ were grafted onto rootstocks and a trial was installed in 1999. Predawn and midday stem water potential (ψ_stem) on cherry trees, measured in 2002, were affected significantly by the rootstock/genotype combination. Cultivars grafted on ‘P. avium’ and ‘Maxma 14’ showed the less negative midday ψ_stem, –1.36 and –1.42 MPa respectively, so these rootstock genotypes perhaps induced a higher drought resistance to the scion. Recorded data show that the scion-rootstock interaction with regard to production performance under water deficits may be an important consideration in cherry tree planting strategies.     

The effects of daminozide and under-soil heating on the growth of radish under winter conditions

The growth of radish cultivars ‘Saxa’, ‘Saxerre’, ‘Serra’, ‘Istar’, ‘Cherrybelle’ and ‘Robino’ was compared at 7 and 12°C under winter glasshouse conditions. ‘Serra’ alone produced marketable storage roots by 63 days at 7°C, but root weight was no greater at 12 than at 7°C; only ‘Robino’ produced significantly larger roots at the higher temperature. Under-soil heating applied to ‘Cherrybelle’ and ‘Robino’ grown at an air temperature of 7°C increased root growth, particularly in ‘Cherrybelle’. Daminozide treatment at 7°C increased total and storage root weight and root:shoot ratio of both cultivars. At 12°C, the only significant effect of daminozide treatment was reduced shoot weight in ‘Robino’.     

Flowering performance and yield of established and recent strawberry cultivars (Fragaria × ananassa) as affected by raising temperature and photoperiod

Plants of six strawberry cultivars were raised under controlled conditions and tested for flowering and yield potential. Short days (SD) at intermediate temperatures for 4 weeks in August induced profuse flowering in subsequent long days (LD) in all cultivars except the late-flowering ‘Malwina’. LD conditions induced flowering only in ‘Nobel’, which has an everbearing parent. ‘Nobel’ and ‘Saga’ exhibited broad temperature adaptation for SD floral induction, which was generally reduced or suppressed at 9 and 27°C. After autumn planting, all cultivars flowered most abundantly in plants raised in SD and intermediate temperatures. Flowering was earliest in ‘Nobel’ and ‘Rumba’. Plants that did not reach floral commitment after 4 weeks in SD continued and completed induction under subsequent natural SD conditions after planting in the field, demonstrating the capability of fractional induction. Berry yield varied in parallel with flowering in the field and was always higher in plants raised under SD conditions. The traditional cultivars ‘Florence’ and ‘Sonata’ out-yielded the more recent cultivars. Some cultivars lost more than two thirds of their initiated flowers during the winter with obvious consequences for their yields. With proper raising management, acceptable yields were obtained after autumn planting even in a cool Nordic climate.     

Growth of Vitis vinifera L. and Vitis aestivalis Michx. as Affected by Temperature

Abstract

Four European (Vitis vinifera L.) winegrape cvs., ‘Semillon’, ‘Pinot Noir,’ ‘Chardonnay’, and ‘Cabernet Sauvignon’, and one American (Vitis aestivalis Michx.) winegrape cv. ‘Cynthiana’, were subjected to three temperature regimes in growth chambers set at 20/15°C, 30/ 25°C, or 40/35°C, for 16/8 hr day/night to determine the influence of temperatures on vine growth and development. In general, the best temperature for shoot and root growth 28 days after temperature treatments was 20/15°C for ‘Semillon’, ‘Cabernet Sauvignon’, and ‘Cynthiana’, and 30/25°C for ‘Pinot Noir’ and ‘Chardonnay’. Although 40/35°C reduced number of leaves, shoots, tendrils, and internodes, total leaf area (LA), and total shoot biomass of all the cultivars, the reduction was more pronounced in ‘Cynthiana’ than in the European cultivars. The average reduction in number of leaves at 40/35°C for the European cultivars was 47%, compared with 92% for ‘Cynthiana’. The two types of grapes adapted differently to high temperature. Shoot growth in the European cultivars continued under high temperature, whereas growth ceased in ‘Cynthiana’. Roots of ‘Cynthiana’, however, were less susceptible to the adverse effect of high temperatures than were the shoots. This study shows that the European cultivars were relatively more tolerant to high temperature than the American cultivar and they have a potential for production of wine in the climate of south central Kansas.     

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.     

Effects of far-red light/temperature DIF and far-red light/temperature pulse combinations on height of lily hybrids

Summary

Potted bulbs of ‘Nellie White’, ‘Sunray’ and ‘Stargazer’ representing three lily hybrids [Easter (Lilium longiflorum Thunb.), Asiatic and Oriental, respectively], were forced in a glass greenhouse under three lighting regimes namely, 8.h photoperiod (8 PP) by using blackout between 1600 hours and 0800 hours to eliminate twilight; 8 PP extended with 1.h of low intensity far-red radiation (9 PP) at the beginning of the dark period; or ambient. All three lighting regimes were in a greenhouse with either a +5°C or a -5°c DIF (= T_day ±T night ) regime, while maintaining the same 24.h temperature. In a second experiment, two cultivars of each of the three lily hybrids were also grown under the same three lighting regimes with a constant day/night temperature but with either a 15°cor 25°c pulse for 3.h from 1500–1800.hours to coincide with the far-red supplementation for 9 PP. Both experiments were done during the winter and repeated the following year. Within each DIF treatment, plants which received light containing far-red at the end and start of the day (ambient) or beginning of night (9 PP) were taller than those under short day (8 PP). Plants grown under either 8 PP or ambient were taller under +DIF than under -DIF, except when 8 PP was extended with 1.h of far-red, in which case plant height was the same for either DIF. ‘Nellie White’ reacted the strongest to far-red as well as to DIF followed by ‘Sunray’ and then ‘Stargazer’. For ‘Nellie White’, the stem dry weight was increased by far-red radiation at the beginning of the dark period compared with short day or ambient, while the opposite was found for the leaf and bulb dry weights. However, total dry weight of plant was not affected by either DIF or lighting treatment. In the second experiment, plant height was not significantly affected by an end of day temperature pulse of -5°c for either the 9 PP or ambient regimes compared with a +5°c pulse.     

The Effect of a Substrate Containing Arbuscular Mycorrhizal Fungi and Rhizosphere Microorganisms (Trichoderma,Bacillus, Pseudomonas and Streptomyces) and Foliar Fertilization on Growth Response and Rhizosphere pH of Three Strawberry Cultivars

Abstract

Vegetatively propagated plants of three strawberry cultivars-‘Senga Sengana’, ‘Elsanta’ and ‘Kent’-were grown for 20 weeks in rhizoboxes filled with 1.85 kg of sterilized mineral soil. Ten plants were treated with an N-P-K foliar fertilizer (F, control), or inoculated with a substrate containing arbuscular mycorrhizal fungi, Trichoderma viride and rhizosphere bacteria (PGPR-Plant Growth Promoting Rhizobacteria) without any fertilization (M), or inoculated with the mixture of microorganisms and treated with the foliar fertilizer (MF). Total plant biomass was increased by the M treatment in all cultivars. M treatment resulted in higher total root length and number of root tips in ‘Senga Sengana’, whereas the other two cultivars showed different responses of root morphology. Shoot/root ratio was decreased by the M and MF treatments in comparison with control plants. Foliar fertilization of inoculated plants caused different growth responses in the three cultivars and a general decrease of root growth. After the MF treatment, the biomass of ‘Senga Sengana’ increased and the biomass of ‘Elsanta’ and ‘Kent’ decreased. Inoculation with the mycorrhiza-PGPR substrate increased rhizosphere pH irrespective of foliar fertilization. Plant mineral content was highly modified by the treatments in all the cultivars examined. In particular, changes were noted in N, P, K, Fe, B and Mn uptake. The results show an interaction between foliar fertilization and root inoculation with microorganisms, as well as genotype-dependent influences, on growth responses and rhizosphere pH of strawberry plants.     

Study of some factors affecting the growth and development of myoga (Zingiber mioga Roscoe)

In order to optimise production of the edible flower buds produced by myoga (Zingiber mioga Roscoe) a greater understanding of the growth and development of the plant and factors influencing flower initiation and development are required. The vegetative growth phase in myoga was characterised by a distinct period of pseudostem development from the planted rhizome piece followed by an extended period of rhizome growth from both the base of pseudostems and the planted rhizome piece. The transition from pseudostem formation to the initiation of rhizome growth occurred at the same time as the dry weight of the planted rhizome piece ceased to decline. Flower bud initiation and development occurred over an extended period, beginning soon after the commencement of new rhizome growth and ending prior to foliage senescence. Flower buds were observed at the terminal meristem of first, second, third and fourth order rhizomes. Increasing temperatures stimulated both increased vegetative growth and flower bud initiation and development. Low flower bud yields recorded under conditions of low temperature were the result of reduced rate of floral initiation and not abortion of flower buds. Increased shading of plants grown under glasshouse conditions resulted in reduced flower bud yield and similarly the response resulted from decreased initiation rather than abortion.     

Effects of basal temperature on the rooting of hardy hybrid Rhododendrons

The effects of 3 basal temperatures; 15°, 20° and 25°C, on rooting of the hardy hybrid Rhododendron cultivars ‘Pink Pearl’, ‘Mrs. R.S. Holford’ and ‘Fastuosum Flore Pleno’ have been studied.A temperature of 15°C gave least rotting in all 3 cultivars and therefore more cuttings survived to root. Rotting increased and rooting decreased with increasing temperature.In cuttings without evident rotting, 25°C gave better rooting than 15°C, indicating that with improved control of disease, propagation at the higher temperature may be beneficial.The ease of rooting in unrotted cuttings was similar in R. ‘Fastuosum Flore Pleno’ and R. ‘Pink Pearl’ but lower in R. ‘Mrs. R.S. Holford’. Rotting was greatest in R. ‘Mrs. R.S. Holford’ and least in R. ‘Fastuosum Flore Pleno’.     

Root System Distribution of Highbush Blueberry Crops of Various Ages in Medium-Textured Soils

The paper deals with the spatial distribution of root density in highbush blueberry plantations of various ages for a proper planting distance recommendation and a better irrigation and fertilization management. The environmental conditions consist of sandy-loamy soils and a continental temperate climate. Two highbush blueberry cultivars were studied, ‘Bluecrop’ and ‘Blueray’. Root density (RD) and density of root cross-sectional area (RCSA) were investigated for various root diameters. It was found that the prevalent type of roots in highbush blueberry crops is the hair type, with root diameters less than 0.1?mm. Both RD and RCSA decreased with distance from plant and with soil depth; the 38-year-old crop showed a more developed root system versus the 8?year-old crop. In both cases the roots did not grow more than 0.6?m laterally and more than 0.7?m deep. According to these results, the planting distances in highbush blueberry could be reduced to substantially increase the number of plants/ha and fruit yield. Irrigation application should be carried out to wet a proper soil volume, about 0.6–0.7?m deep for older crops, and about 0.5?m deep for younger crops.     

Rooting of peach hardwood cuttings for the meadow orchard

In order to make peach meadow orchard systems feasible, the possibility of propagating peaches by hardwood cuttings and thus reducing the establishment cost of this extremely high-density planting system was examined.A medium temperature of 25°C was harmful to auxin-treated peach cuttings, but excellent rooting could be obtained at a temperature as low as 12°C. Further trials conducted under outdoor conditions in winter in the coastal plain of Israel, with a soil temperature of 12–14°C, did not show any effect of timing on rooting, providing the cutting was taken mature enough (after mid-November) and not later than about 6 weeks prior to bud break. In 30 days root initiation started. Although variations were found between cultivars, 1500 mg/l of indole butyric acid in a 5-second base-dip was found to act well with most cultivars. Good aeration was shown to be critical for good root formation. Leaving the cutting for 1 month in damp sand prior to planting in orchard soil was satisfactory. An area of a few hectares of commercial meadow orchards has already been established with this method.     

Rate of nitrogen application during the growing season alters the response of container-grown rhododendron and azalea to foliar application of urea in the Autumn

Summary

One-year-old rhododendron (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron ‘Cannon’s Double’) plants grown at different nitrogen (N) fertilisation rates were used to assess the influence of soil N applications during the growing season, and foliar applications of urea in the Autumn, on N uptake and accumulation, and plant growth in the following Spring. N uptake efficiency declined linearly during the first growing season with an increasing rate of N fertilisation. For both cultivars, foliar urea application in the Autumn significantly increased plant N content without affecting plant size, regardless of plant N status. Leaves of rhododendron accumulated more N than other plant structures. Plants sprayed with foliar urea in the Autumn had more new growth the following Spring than plants receiving no urea, regardless of whether the plants received fertiliser in the Spring. For azalea, N uptake in the Spring was, in general, not affected by applications of urea during the previous year. For rhododendron, urea application in the Autumn decreased N uptake the following Spring. For both cultivars, increasing N availability during the growing season increased the ratio of above-ground to below-ground dry weight. Our results suggest that combining optimum N applications during the growing season with foliar application of urea in the Autumn can improve N uptake efficiency, increase N storage, and optimise growth in Rhododendron.     

Effect of the plant raising environment,transplant weight and date of transplanting on the subsequent growth and development of leeks (Allium porrum L.) grown for early production

Leek transplant weight at planting was greater for a given period of growth at 23°C than at 9°C but was unaffected by nutrition. A single line fitted to all the data, using a time-scale based on ‘effective day-degrees’ (with a base of 4°C and an upper limit of 23°C) accounted for over 76% of the variance in transplant weight at planting. Plant weight at harvest was positively related to transplant weight and fitting straight lines to each of the early and late harvest data sets from all the experiments accounted for 75% of the variance in plant weight at harvest. There were no ‘carry-over’ effects of temperature or nutrition from the plant-raising phase other than those on transplant weight. It was calculated, using data from two of the experiments where transplanting date was a factor, that yields fell by between 0.4 to 1.61 ha“1 for each week’s delay in planting over the period early April to mid-June. This loss in yield could be compensated by planting larger plants; 300 g plants could be produced in early August by planting 0.6 g, 0.9 g and 1.7 g plants in mid-April, mid-May and early/mid-June, respectively. The number of plants with flower initials at harvest increased with an increase in transplant weight and exceeded 10% with transplants of 0.5 g fresh weight or more and, for comparable transplant weights, was substantially greater from plants raised at 9° than 12°C. Flower initials were present even in crops from plants raised at 23°C. Transplants raised at 9°C produced up to 30% bolters at harvest but bolters were almost completely absent in crops established from plants raised at 12°C, 18°C or 23°C. Small plants (<0.4 g fresh weight) with 2-3 visible true leaves responded to cold.     

Physiological and anatomical responses of calendula (Calendula officinalis L.) cultivars to heat-stress duration

It is necessary to identify the heat-tolerant cultivars of bedding plants in order to cope with the challenges of the global warming. The physiological and anatomical responses of four calendula cultivars (Candyman’, ‘Zen’, ‘Indian Prince’, and ‘Pacific Beauty’) to four duration levels (0, 7, 14 and 21 days) of heat stress (in a mean range of 35–42°C), were investigated after their establishment under greenhouse conditions. The results indicated that calendula cultivars displayed different responses to various heat duration levels in most parameters. Although the gas exchange of ‘Candyman’ was the highest in control treatment, it showed a considerable reduction in all levels of stress durations. In contrast, ‘Indian Prince’ maintained gas exchange and chlorophyll content and exhibited the most resistance to heat stress among others, especially for longer duration exposure, which might be resulted from the greater soluble sugar content, higher stomatal density, and thicker leaves. Experiment to assess cell membrane thermostability showed heat stress resulted in significant increase in electrolyte leakage percentage as the incubation temperature of all cultivars was increased. However, the least membrane stability was observed in ‘Zen’, indicating the higher sensitivity of this cultivar to heat-stress conditions in comparison to three other cultivars.     

Evaluation of conditions for in vitro storage of commercial and minor grapevine (Vitis vinifera L.) cultivars

In vitro culture represents a tool for the ex situ conservation of a high number of sanitised plants in a reduced space. However, the culture media and/or other growing conditions need to be optimised to minimising plant growth and storage cost. Growth on MW medium was evaluated in the commercial cultivars ‘Airén’, ‘Bobal’, ‘Chardonnay’, ‘Garnacha Blanca’, ‘Moscatel de Alejandría’, ‘Moscatel de Grano Menudo’, ‘Pedro Ximénez’, ‘Pinot Blanc’, ‘Pinot Gris’, ‘Sauvignon Blanc’, and ‘Tempranillo’; the minor cultivars ‘Chelva’, ‘Valencí Negre’, ‘Valencí Blanc’, and ‘Verdil’; and the endangered cv. ‘Esclafacherre’. Different growth rates were observed among cultivars: those with faster growth need to be subcultured every 1.5–2.0 months; those with the slowest growth every 3.5–4.0 months. The effect of halving the sucrose in MW reduced the growth of the cultivars that grew faster without compromising survival. When IBA was removed from MW, growth was also reduced in some cultivars. Therefore, small modifications of the MW composition are adequate for grapevine in vitro storage under standard incubation conditions. This is an advantage with respect to the change of temperature used in other work to achieve growth reduction, and allows the use of the same chamber for different in vitro culture procedures.     

Temperature effects on dormancy,bud break and spear growth in asparagus (Asparagus officinalis L.)

Summary

The effects of the length of chilling, chilling temperature and growing temperature on dormancy of asparagus crown buds and subsequent rates of spear growth were examined. The results showed that prior chilling enhanced bud break at low growing temperatures and stimulated the growth of spears.Thus, chilling should facilitate commercial production by hastening bud break and spear growth rates at lower temperatures. If sufficient chilling was given, the minimum temperature for rapid bud break was approx. 12.5°C for ‘Rutgers Beacon’ and ‘Jersey Giant’, and around 10°C for ‘UC 157’ and ‘Apollo’. The optimum chilling temperature appeared to be closer to 5°C than to 10°C or 2°C for ‘Rutgers Beacon’ plants grown at 12.5°C. Increasing the growing temperature had a significant effect on the relative spear growth rate (RSGR) in all cultivars. Prior chilling had no effect on the RSGR for ‘Dariana’ and ‘Apollo’; but, for ‘UC 157’, chilling plants at 5°C for 5 or 10 weeks increased growth rates at 12.5°C and at 20°C. These results demonstrate that release of bud dormancy and spear growth rates depended not only on the growing temperature, but also, at least in some cultivars at some temperatures, on the duration and temperature of chilling during the previous Winter.     

Investigations on Chlorosis of Fruit Trees.: III.—A Chlorosis of Plums Due to Potassium Deficiency.

Summary

Grafting is a suitable method to control soil-borne diseases in melon (Cucumis melo L.) crops. To date, several Cucurbita species and their inter-specific hybrids have been tested as rootstocks. However, graft-scion incompatibility and lower fruit quality have prevented their commercial use. The wild accession ‘Pat 81’ ssp. agrestis of C. melo is highly resistant to Monosporascus cannonballus Pollack et Uecker root rot, and develops a root system that is more suitable to withstand infested soils than that of cultivated melon. The potential of ‘Pat 81’ as a rootstock for melons (e.g., ‘Piel de Sapo’ type, C. melo ssp. melo) compared with the popular rootstock ‘RS 841’ (Cucurbita maxima Cucurbita moschata) has been evaluated here. The response of grafted plants to Monosporascus root rot disease, and rootstock effects on plant performance and fruit quality have been investigated using both classical methods and modern technologies (e.g., root image analysis and real-time PCR). The results indicate that, during infection, the root system of ‘Pat 81’ adapts to the needs of the aerial part of the ‘Piel de Sapo’ scion, displays a high level of resistance to M. cannonballus (similar to ‘RS 841’), and provides the plant with more healthy roots, with a higher root/vine biomass ratio compared with non-grafted ‘Piel de Sapo’. In addition, ‘Pat 81’ rootstock retains its favourable root structure (i.e., larger total length and root area) to withstand soil stress. In healthy soils, ‘Pat 81’ rootstocks had less effect on fruit quality than ‘RS 841’, leading to a lower percentage of non-marketable products. The high resistance of ‘Pat 81’, and its reduced effect on fruit quality, point to it as a good rootstock for the grafting of melons to resist M. Cannonballus infested soils.     

The effect of temperature on growth and dry matter production of lychee seedlings

In lychee (Litchi chinensis Sonn.), high day/night temperatures ($\text{30}\text{25}$, $\text{25}\text{20}$, $\text{20}\text{15}\text{°}\text{C}$ compared to $\text{15}\text{10}\text{°}\text{C}$) increased stem extension, node and leaf production and plant dry weight in seedling selections of 6 cultivars (‘Bengal’, ‘Haak Yip’, ‘Kwai May’, ‘Gee Kee’, ‘Tai So’ and ‘Wai Chee’). The mean daily base temperature for shoot growth (node production) was estimated by linear correlation to be 11.0°C for the seedlings. High temperatures also increased the proportion of leaf and decreased the proportion of root in the total dry weight. There was a strong effect of cultivar on all aspects of growth, but the responses to temperature were similar.This experiment shows that temperatures in many tropical and warm sub-tropical areas where lychees are grown are too high to induce satisfactory vegetative dormancy prior to floral initiation. The assessment of lychee seedlings for low vigour in a heated glasshouse appears to be a useful technique for the initial screening of adapted genotypes (which flower and fruit under warm conditions) prior to field evaluation.     

Bulbing responses of two cultivars of red tropical onions to photoperiod,light integral and temperature under controlled growth conditions

Summary

The effects of photoperiod, light intensity and temperature on bulb formation and bulb structure of two tropical onion cultivars were investigated. From an initial experiment it was observed that the number of true scales and sheath scales differed significantly between the cultivars ‘Red Creole’ and ‘Agrifound Dark Red’. When these two cultivars were given 11, 12 and 13 h photoperiod treatments, it was found that both cultivars needed at least 12 h photoperiod for bulb formation. Modify the R/FR ratio from 1.22 to 1.16 in the final hour of the 11 h light period did not induce bulbing. The 13 h photoperiod increased the number of true scales and decreased the number of sheath scales compared with the 12 h photoperiod in both cultivars but total scale + leaf sheath numbers remained nearly constant. When onion plants were grown under 0%, 25%, 50% and 75% shading treatments, (12 h photoperiod), only plants receiving 0% and 25% shading bulbed. Low light intensity decreased the number of true scales and increased the number of sheath scales. Four temperature regimes were compared in a growth room experiment. Plants under the 29°348C treatment bulbed within two weeks and matured within six weeks. However, plants receiving the 25°308C treatment delayed bulb initiation more than those plants receiving 17°228C and 21°268C treatments. At the lowest temperature, bigger bulbs with thick necks were produced. This may be due to changes in bulb structure since at low temperature, the number of sheath scales was increased, however the number of true scales remained relatively constant in both cultivars. Dormant leaf initials decreased with decreasing temperature while the number of secondary meristems significantly increased. The results suggest that ‘Red Creole’ was more responsive to shorter photoperiods, bulbing earlier than ‘Agrifound Dark Red’. There was no significant difference in time to bulbing in response to temperature between the two cultivars if measured by bulbing ratio however there were differences in bulb structure which suggested that ‘Red Creole’ bulbed earlier. These effects may be due to the breeding histories of the two cultivars. It is suggested that studying bulb structure may provide a useful method of interpreting onion bulbing responses.