Vegetative Flush Research Articles

Effects of Magnesium-Sulfate on Leaf Chlorosis, Plant Growth and Nutrient Uptake in Camellia sasanqua ‘Shishi Gashira’

Abstract A ‘V’-pattemed chlorosis of older leaves is frequently observed on specific cultivars of container-grown Camellia sasanqua. Symptoms are expressed during the flowering period and as the first vegetative flush of the season develops in early spring. Symptomatic leaves eventually senesce and subsequent vegetative flushes appear healthy. In the following study, container-grown Camellia sasanqua ‘Shishi Gashira’ were fertilized with 500 ml of nutrient solution containing one of five treatments: 0.0, 4.0, 10, 20, or 40 g/liter magnesium sulfate heptahydrate (MgSO4·7H2O) per 19-liter container every two weeks for nine months to determine if chlorosis could be prevented. Nutrient analyses were conducted on all plant organs to determine if there was a correlation between nutrient partitioning to different organs and the expression of leaf chlorosis. Supplemental MgSO4·7H2O fertilization increased the Mg concentration in the roots, stems, leaves and flowers, and increased the sulfur concentration only in the leaves and stems. Calcium concentration in all organs decreased and potassium concentration in the leaves and stems decreased with increased fertilization rates. Fertilization with MgSO4·7H2O prevented the development of ‘V’-patterned chlorosis but did not affect plant dry weight.

Root growth, cytokinin and shoot dormancy in lychee ( Litchi chinensis Sonn.)

Potted lychee trees (cv. Tai so) with mature vegetative flushes were grown under three day/night temperature regimes known to induce floral (18/13 °C), intermediate (23/18 °C) and vegetative (28/23 °C) shoot structures. Root and shoot growth was shown to alternate at all temperatures, with root growth occurring during shoot dormancy and in the initial stages of shoot emergence. As temperature decreased, the rate of root growth decreased and the length of the shoot dormancy period increased. Increasing the period of the endogenous shoot/root growth rhythm was sufficient to induce floral initiation. At all temperatures, shoot dormancy was broken after a similar amount of root growth. This occurred at approximately 3, 6 and 8 weeks for 28/23, 23/18 and 18/13 °C, respectively. The concentration of the cytokinin, zeatin riboside, increased in parallel with an increase in root growth rate, reaching a peak in terminal buds just prior to shoot emergence. Application of zeatin riboside to dormant buds resulted in bud-break, but full emergence did not occur. It is proposed that root growth has a strong influence on the period of shoot dormancy, possibly through the initiation of bud-break by zeatin riboside, and can influence emerging shoot structure.

Impact of root and shoot temperature on bud dormancy and floral induction in lychee ( Litchi chinensis Sonn.)

Potted lychee trees (cv. Tai so) with mature vegetative flushes were grown under three day/night temperature regimes known to induce floral (18/13 °C), intermediate (23/18 °C) and vegetative (28/23 °C) shoot structures. Heating roots respective to shoots accelerated bud-break and shoot emergence, but reduced the level of floral initiation in emergent shoots. At 18/13 °C, root temperatures of 20 and 25 °C decreased the period of shoot dormancy from 9 weeks to 5 and 3 weeks, respectively. A root temperature of 20 °C also increased the proportion of both leafy and stunted panicles to normal leafless panicles, and reduced the number of axillary panicles accompanying each terminal panicle. A root temperature of 25 °C produced only vegetative shoots. At 23/18 °C, heating roots increased the proportion of vegetative shoots and partially emerged buds to leafy and stunted panicles as well as accelerating bud-break. Cooling of roots in relation to the shoot resulted in non-emergence of buds at both 28/23 and 23/18 °C. Bud-break did not occur until root cooling was terminated and root temperature returned to that of the shoot. At 23/18 °C, subsequent emergent shoots had a greater proportion of leafy panicles relative to control trees. At 28/23 °C, all emergent shoots remained vegetative. Lychee floral initiation is influenced by both root and shoot temperature. Root temperature has a direct effect on the length of the shoot dormancy period, with high temperatures reducing this period and the subsequent level of floral initiation. However, an extended period of dormancy in itself is not sufficient for floral initiation, with low shoot temperatures also a necessary prerequisite.

Xylem-sap zeatin-riboside and dihydrozeatin-riboside levels in relation to plant and soil water status and flowering in ‘Mauritius’ lychee

The effects of autumnal water stress on the levels of zeatine-riboside and dihydrozeatin-riboside in the shoot xylem-sap and on the intensity of flowering in the following year were studied in commercial lychee ( Litchi chinensis Sonn.) during the 1995/1996 season. Four irrigation treatments were initiated at the beginning of October coinciding with the end of the second vegetative flush after harvest as follows: 0.5, 0.25, 0.125 and 0 Class A pan evaporation coefficient, designated as 100, 50, 25 and 0%, respectively, were applied. Soil and midday stem water potentials were determined several times during October, after the beginning of treatment. Xylem-sap concentrations of trans-zeatin-riboside ( t-ZR) and dihydrozeatin-riboside (DHZR) were determined 20 days after the start of the irrigation treatments. Both soil and midday stem water potentials decreased with the decrease in the irrigation levels. Flowering intensities in the following spring were higher after the reduced irrigation treatments than in the control (100%). DHZR and t-ZR concentrations in the xylem-sap increased with decreasing irrigation level, down to the 25% irrigation level. Cessation of irrigation (0%) resulted in a steep decrease in the t-ZR concentration and a further increase of DHZR. The relationships between plant and soil water status, cytokinin xylem-sap content and flower bud differentiation reported herein suggest that moderate water stress is sufficient to induce fruit bud differentiation without any visible damage to the trees.

Interaction of temperature and vegetative flush maturity influences shoot structure and development of lychee ( Litchi chinensis Sonn.)

Potted lychee trees (cv. Tai so) of varying vegetative flush maturity were grown under a range of temperature regimes and monitored for subsequent shoot structure and development. A combination of low temperature (15/17 or 18/13 °C day/night) and high vegetative flush maturity was necessary for floral initiation to occur. Exposure to high temperatures (28/23 °C) invariably resulted in the production of vegetative shoots, irrespective of flush maturity. Strong floral initiation was marked by the emergence of terminal panicles and accompanying axillary panicles. A decrease in vegetative flush maturity or increase in temperature (e.g. 23/18 °C) resulted in a decrease in axillary shoot formation and the production of several intermediate shoot structures. These included leafy panicles, stunted panicles, partially emerged buds and non-emergent swollen buds, often produced on the same tree. At 23/18 °C, closer synchronisation of initial flush maturity was required for the production of a consistent shoot-type. Trees with synchronised mature flushes (I-2) at 23/18 °C resulted in the production of swollen terminal buds. Healthy trees were maintained in this state for at least 11 months. These results indicate that both temperature and flush maturity can influence subsequent shoot structure of lychee. In the absence of either a strong floral temperature (18/13 °C) or strong vegetative temperature (28/23 °C), slight differences in initial flush maturity have greater impact on the type of emerging shoot formed.

Flowering and shoot elongation of lychee in eastern Australia

We investigated the effects of the timing of shoot elongation on the flowering of lychee (Litchi chinensis Sonn.) in eastern Australia. Trees of cv. Kwai May Pink growing in Alstonville (lat. 28.9° S) were pruned during spring and summer, and subsequent shoot elongation was measured until the following spring. New shoots grew by discrete flushes, with the trees initiating 3, 2, or 1 vegetative shoots prior to winter, according to the pruning sequence. Shoots were vegetative when the mean temperature during early flush development was above 17-19°C, and floral at lower temperatures. Trees with successive flushes commencing in February (late summer) and June (early winter) were more likely to flower than trees with flushes commencing in April and August, because the weather conditions in June were cooler than those in August and more likely to favour induction. The importance of cool weather conditions during early flush development for floral determination was not significantly affected by the number of vegetative flushes to develop between pruning and winter. Having shown that the phase of recurrent flushing affects flowering, we sought to model the process in order to recognise reproductive and non-reproductive cycles along Australia's north-eastern seaboard, and to develop a management strategy for the promotion of flowering. From the results of the Alstonville pruning trial, the interval between successive flushes was regressed against the mean product of daily irradiation and mean daily temperature (°C.MJ/[m2.day]) during the interval. The regression was used in conjunction with long-term weather records to estimate the flush commencement dates required for the completion of 1 or 2 vegetative flushes by the winter solstice at different latitudes. The earliest date for the completion of 1 flush ranged from 16 February in northern New South Wales (lat. 30° S) to 13 March in northern Queensland (lat. 17° S). To test the model, a pruning trial was conducted near Mareeba (lat. 17° S). Trees pruned on 10 February, estimated to produce ≈ 1.5 flushes prior to winter (i.e. flushes in late autumn and early spring, but not in winter), flowered poorly and had low yields. In contrast, trees pruned on 11 March, estimated to produce 1 vegetative flush by winter, had good flowering and yields. Thus, strategic pruning after harvest can be used to manipulate flushing times, so that new, potentially flowering shoots emerge in winter. Cool temperatures are still required for successful flowering, and we provide estimates of the likelihood of such weather in the major growing areas by calculating the annual number of days with a mean temperature <20°C. For Cairns (lat. 16.9° S) the number of such days varied from 0 to 39 from 1888 to 1993, which is consistent with the irregular flowering of lychee in coastal northern Queensland. Our work is the first demonstration for any species that the phase of recurrent flushing affects flowering, and emphasises the interplay between a plant's endogenous developmental cycle and seasonal variations in weather.

358 Nitrogen Fertilization and Lychee Flowering and Production in Southern Florida

Despite the increasing popularity in American markets of the fruit of the illustrious lychee (Litchi chinensis Sonn.), unreliable flowering and yield has had serious impacts on lychee growers in southern Florida. Lychee flowering is normally induced by chilling temperatures. Unpredictable weather, high rainfall, and excessive nutrients cause unreliable flowering in southern Florida. Although growers have no control over the weather, they need to be able to manage the growth, vigor, and reproduction of trees through practices that optimize flowering. When excessively watered and fertilized, lychee trees grow vigorously with frequent vegetative flushes every 2 to 3 months. The lack of maturity of these late vegetative flushes prevents flower stimulation from mild temperatures in January and February, when flowering typically occurs on trees that have not experienced vegetative flushes in the late fall or early winter. Thus, by adopting nitrogen fertilizer management practice, growers should be able to induce abundant flowering even in mild winters. Our preliminary results demonstrated that timing and rates of applications of nitrogen fertilizer significantly affected concentrations of soil and leaf N. High nitrogen levels in the leaves induced more vegetative flushes and less flowering, and consequently less fruit yield.

531 CMN-Pyrazole-induced Abscission of Mature `Valencia' Oranges in Relation to Young Fruit, Root, and Shoot Growth

The seasonal abscission response of mature `Valencia' oranges [Citrus sinensis (L.)Osb.] to 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMN-Pyrazole) was examined in relation to young fruit, shoot, and root growth. CMN-Pyrazole dramatically increased ethylene production in fruit and effectively reduced the fruit detachment force (FDF), except in a period of reduced response to CMN-Pyrazole in early May. Root growth was inhibited by trunk girdling, in combination with removal of spring vegetative flushes and flowers, but not by their removal alone. During the responsive period, there was no difference in both ethylene production and FDF of CMN-Pyrazole-treated mature oranges between 1) the unmanipulated trees and those manipulated by either 2) girdling, removal of spring flushes and flowers, or 3) removal of flushes and flowers alone. However, during the less-responsive period, ethylene production in CMN-Pyrazole-treated mature oranges was significantly lower while the FDF was higher from non-manipulated trees than from trees treated by either girdling and removal of flush, or only removal of flush. There was no difference in either ethylene production or FDF of CMN-Pyrazole-treated mature oranges between trees manipulated by girdling and removal of flush, and those by removal of flush alone. Flush growth terminated at least 2 weeks before the onset of the less responsive period. This suggests that the hormones from rapidly growing young fruit may be responsible for the less responsive period.

Ultra-enhanced spring branch growth in CO 2-enriched trees: can it alter the phase of the atmosphere’s seasonal CO 2 cycle?

Since the early 1960s, the declining phase of the atmosphere’s seasonal CO 2 cycle has advanced by approximately 7 days in northern temperate latitudes, possibly as a result of increasing temperatures that may be advancing the time of occurrence of what may be called ‘climatological spring.’ However, just as several different phenomena are thought to have been responsible for the concomitant increase in the amplitude of the atmosphere’s seasonal CO 2 oscillation, so too may other factors have played a role in bringing about the increasingly earlier spring drawdown of CO 2 that has resulted in the advancement of the declining phase of the air’s CO 2 cycle. One of these factors may be the ongoing rise in the CO 2 content of the air itself; for the aerial fertilization effect of this phenomenon may be significantly enhancing the growth of each new season’s initial flush of vegetation, which would tend to stimulate the early drawdown of atmospheric CO 2 and thereby advance the time of occurrence of what could be called ‘biological spring.’ Working with sour orange ( Citrus aurantium L.) trees that have been growing out-of-doors in open-top chambers for over 10 years in air of either 400 or 700 ppm CO 2, this hypothesis was investigated by periodically measuring the lengths, dry weights and leaf chlorophyll concentrations of new branches that emerged from the trees at the start of the 1998 growing season. The data demonstrate that the hypothesis is viable, and that it might possibly account for 2 of the 7 days by which the spring drawdown of the air’s CO 2 concentration has advanced over the past few decades.

658 Processes Influencing Floral Initiation and Bloom: The Role of Phytohormones in a Conceptual Flowering Model

The reproductive phenology of temperate tree fruit species, such as apple and peach, will be briefly introduced and compared to the reproductive phenologies of several tropical and subtropical tree fruit species. Conceptual models of citrus and mango flowering will be described which help to understand the physiological mechanisms of flowering and vegetative flushes in trees growing in subtropical and tropical environments. Possible roles for auxin and cytokinins in shoot initiation and for gibberellins and a putative florigenic promoter in induction will be discussed as they relate to the physiology of flowering and vegetative flushes of tropical species. Successful application of these conceptual flowering models in controlling flowering of citrus, mango, lychee, and longan through the use of growth regulators and other horticultural management techniques will be described.

Epidemiology of Mango Malformation in Guerrero, México, with Traditional and Integrated Management.

The temporal progress of malformation (MM) of mango (Mangifera indica) was studied from 1993 to 1995 with three management technologies applied to commercial plantations in North Guerrero, Mexico. Management influenced shoot production and thus determined the dynamics of epidemics. Environmental factors also affected disease incidence, particularly through an apparent effect on inoculum dispersal. In general, integrated management (IM), consisting of pruning, acaricide, and fungicide sprays, resulted in slower rates of epidemic development, lower levels of initial and final disease, and lesser areas under the disease progress curves. In the first cycle, IM increased yield per tree by 51% in relation to high technology (HT) and 74% in relation to lower traditional technology (LT), representing a benefit-cost rate of 2.8 and 3.3, respectively. Change of malformation incidence was correlated positively with the number of macroconidia of Fusarium sp. trapped in the canopy (r = 0.90, P = 0.0001) and wind speed (r = 0.83, P = 0.0001); both variables lagged over a 4-month period. The greatest change in malformation occurred during the main vegetative flush, which occurred 3 to 6 months after picking the fruit (May). The accumulated proportion of diseased shoots was correlated with the following variables measured over a 1-week period: average maximum daily temperature (r = -0.68, P = 0. 01), average temperature per hour (r = -0.59, P = 0.04), average number of hours with relative humidity ≥60% (r = -0.82, P = 0.001), and wind speed (r = 0.94, P = 0.0001). In general, the greatest spore density was found during the rainy season, with a morning periodicity showing the highest correlation with wind speed (r = 0.812, P = 0.0001). F. subglutinans was isolated consistently from diseased (86%) and asymptomatic (5%) vegetative and flowering shoots.

Gibberellin and temperature effects on dormancy release and shoot morphogenesis of mango ( Mangiferaindica L.)

Single foliar sprays of gibberellic acid (GA 3) (10–250 mg l −1) were applied during cool or warm temperatures to determine their effects on shoot initiation and morphogenesis in mango ( Mangifera indica L.) cv. Keitt and Tommy Atkins. Dormant, non-differentiated axillary buds were released by removing the apical inflorescence (deblossoming) in flowering shoots, or by heading the terminal vegetative flush (intercalary unit) in vegetative stems. Buds of non-treated and GA 3-treated stems initiated growth during exposure to cool (about 26°C day/15°C night outdoors or 18°C day/10°C night in a growth chamber) or warm temperatures (outdoors at about 29°C day/25°C night or 30°C day/25°C night in a growth chamber). Buds initiated inflorescences despite GA 3 treatment when morphogenesis occurred during exposure to cool, floral-inductive temperatures outdoors or in the growth chamber. A single GA 3 treatment delayed initiation of inflorescences on deblossomed orchard stems, but not on headed vegetative stems. GA 3 treatment resulted in vegetative shoot production only when buds differentiated during exposure to warm temperature conditions either outdoors or in a growth chamber. Thus, GA 3 delayed inflorescence initiation but did not cause vegetative morphogenesis when bud differentiation occurred in cool temperatures. In contrast to delaying inflorescence initiation in cool temperatures, GA 3 did not delay vegetative growth during warm temperatures. Thus, it is concluded that GA 3 prevents initiation of reproductive shoots of mango rather than inhibiting floral induction.

Effect of Fall Irrigation Level in `Mauritius' and `Floridian' Lychee on Soil and Plant Water Status, Flowering Intensity, and Yield

The effect of fall irrigation level in `Mauritius' and `Floridian' lychee (Litchi chinensis Sonn.) on soil and plant water status, flowering intensity, and yield the following year was studied in a field during 2 consecutive years. At the end of the second vegetative flush after harvest (1 Oct. 1994 and 10 Oct. 1995), four irrigation treatments were initiated: 0.5, 0.25, 0.125, and 0 Class A pan evaporation coefficients designated 100%, 50%, 25%, and 0%. The three lower irrigation levels effectively stopped shoot growth, suggesting the 50% treatment to be the threshold for shoot growth cessation in both years. For both years, flowering intensity and yield in the 100% treatment were lower than those following the other three treatments. Soil and plant water-stress indicators responded to the water-stress irrigation treatments. However soil water-potential values were highly variable relative to plant water potentials. Stem water potential differed more markedly between treatments than leaf water potential. Midday stem water potential appeared to be the best water-stress indicator for irrigation control. Midday stem water potential in both years was correlated with midday vapor-pressure deficit, suggesting that the threshold for irrigation control should take into account evaporative demand.

Prospects for manipulating the vegetative-reproductive balance in horticultural crops through nitrogen nutrition: a review

This review examines the prospects for manipulating the vegetative-reproductive balance in horticultural crops through nitrogen (N) nutrition. It also examines whether incorrect timing or excessive applications of N stimulate vegetative growth at the expense of reproductive growth. Productivity of horticultural crops is dependent on an adequate N status because photosynthetic capacity is dependent on leaf N content per unit area. Efficient N uptake occurs during periods of active growth and depends on active photosynthesis. Most N in exposed leaves is accumulated as protein and the uptake and conversion to protein requires a carbohydrate (CHO) supply. A feedback mechanism has been proposed from shoots to roots in the control of N uptake, because ammonium and nitrate uptake do not increase at supraoptimal concentrations. Stored CHO and nutrients support actively growing shoots and inflorescences and while vegetative and reproductive meristems compete as sinks, fruit growth depends principally on current photosynthesis. Most of the season's N uptake by deciduous trees occurs during the post-fruit maturity period in late summer and autumn in vegetative growth which is remobilized prior to leaf fall in late autumn into storage. The N is redistributed the following spring to support new season leaf and fruit growth. In sand culture studies conducted with 2-year-old peach and apple trees, an N deficiency which led to inadequate tree N reserves in winter inhibited flowering, fruit set and vegetative growth the following spring. N applied during spring is poorly assimilated. For Prunus spp., 90% of the N contained in the spring vegetative flush is derived from storage, indicating that exogenous N applications at that time are unlikely to influence that season's growth. Vegetable crops which have high growth and N uptake rates compared with tree fruit crops (maximum N uptake rate for tomato 66 kg/ha.week v. peach 1.3 kg/ha.week) rely on exogenous N and current photosynthesis to support growth. In studies where very high N rates were applied to horticultural crops, tree crops were unaffected except in citrus where yield was depressed and tree size was unaffected. The growth and yield of most vegetable crops were depressed at high N rates while at these high N rates, tomato yields were increased while vegetative growth was unaffected. Where a depression in tomato growth occurred at high N rates, it was caused by a salt effect, although chloride at the same osmotic potential depresses growth much more than nitrate. In subtropical fruit and nut crops such as lychee, macadamia and avocado, timing and rate of N were not detrimental to yield. Soil N, tree N and CHO reserves buffer against an external N supply and hence the ability of applied N to manipulate the vegetative-reproductive balance. More work is required to establish the extent and subsequent effect of competition between the vegetative flushes and inflorescence growth for subtropical fruit crops in particular.

Vegetative Flush Development and Leaf Area Contribution to Citrus Canopies

The recent infestation of Florida citrus by the Asian citrus leafminer required that more information be obtained about the time interval for a flush to expand and the leaf area contributed by flushes in seasons when leafminer populations are likely to increase and cause leaf area loss. Time for leaf and shoot expansion was determined for spring and summer flush. Leaf area contribution from previous-year and current flushes was determined by seasonal tagging and measuring leaf area for flush in frame areas of 1/4 m2 surface projected to the center of the tree. Flush of 1/3 m length required 30 days to expand from first leaf feathers to full expansion. Summer flush in 1994 was 40% to 45% of total leaf area. Spring and previous year's flush averaged 20% each. Fall flush contributed 5% to 12% to leaf area, more on young, low-bearing trees. Summer flush resulted in more canopy leaf area and previous year's flushes less leaf area than expected by the end of the growing season.

Effect of leaf age, duration of cool temperature treatment, and photoperiod on bud dormancy release and floral initiation in mango

Floral induction in apical buds of container-grown ‘Tommy Atkins’ mango trees occurred after a cool temperature regime of 18 °C day/10 °C night, 12-h photoperiod, was imposed for a minimum period of 3 weeks on trees bearing leaves at least 7 weeks old. Growth of induced buds during exposure to the cool temperature regime appeared to be necessary for floral initiation, since buds resuming growth in warm temperatures (about 28 °C day/22 °C night) immediately after receiving an inductive, cool temperature treatment produced a vegetative flush. Trees bearing younger leaves or chemically forced (thidiazuron or ammonium nitrate application) to resume growth prior to completing 3 weeks of cool temperature treatment also produced vegetative growth instead of inflorescences. Cool temperatures of 18 °C day/10 °C night with either 11-, 12-, 13-, or 24-h photoperiods resulted in floral initiation, whereas only vegetative growth occurred with warm temperatures of 30 °C day/25 °C night using 11- or 13-h photoperiods. Results of this study suggest that floral induction of ‘Tommy Atkins’ mango occurred during bud dormancy in cool temperatures around 15 °C, and that warm temperatures near 30°C prevented floral initiation of induced buds. Cool temperatures rather than a short photoperiod caused floral induction, whereas warm temperatures rather than a long photoperiod inhibited flowering.

Seasonal Fluctuations in the Extent of Colonization of Avocado Plants by the Stem Canker Pathogen Phytophthora citricola

At monthly intervals, plants and stem cuttings of avocado (Persea americana Miller) `Hass' grafted on `Barr Duke' rootstock and `Topa Topa' growing in a lathhouse were wounded and inoculated with the stem canker pathogen, Phytophthora citricola Sawada. The seasonal changes (measured monthly) in the extent of colonization of the avocado plants by P. citricola followed a periodic pattern, with two peaks of colonization during an annual growth cycle. Concentration of free amino acids and total soluble carbohydrates in the plant tissues followed a periodic pattern with two peaks similar to that of canker growth. Months were significantly different for canker size, free amino acids, and total soluble carbohydrates of the bark tissues. The extent of colonization was highest during May-June, after the first vegetative flush, and during November-December, after the second vegetative flush. Total free amino acids of the hark tissue was highly correlated with canker size (r = 0.89). Although the total soluble carbohydrate of the bark tissue was also elevated during the periods of canker development, it showed lower positive correlation (r = 0.45) with canker size. Plants were relatively resistant to colonization through March-April, during the first vegetative flush, and through August-September, during the second vegetative flush. Cankers formed on stem cuttings were generally larger than those of intact plants.

Effect of sampling time and leaf position on leaf nutrient composition of Protea 'Pink Ice'

Seasonal fluctuations in the concentrations of 12 nutrients were assessed over 3 years for Protea 'Pink Ice' in 3 plantings in the Mount Lofty Ranges of South Australia. Nutrient concentrations in youngest fully expanded leaves (YFEL) generally showed strong seasonal trends, reflecting seasonal vegetative and flowering patterns. During May-August and December-February, YFEL concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), sulfur (S), copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) were relatively stable, making these suitable times for sampling. The effects of sampling error and leaf position were also determined. The error associated with our sampling procedure was within acceptable limits (coefficients of variation 45%) for N, P, K, Ca, magnesium (Mg), Na, S, and boron (B). Differences in nutrient composition between YFEL and YFEL - 1, YFEL - 2, YFEL + 1, YFEL + 2, and YFEL + 3 were of little practical significance. Nutrient removal by flowering stems and concentrations of nutrients in different fractions (bloom, stem + leaves, axillary shoots) of flowering stems were determined for each site. Nutrient concentrations in flowering stems were generally lower than in leaves. Nitrogen concentrations in axillary shoots and K concentrations in blooms were significantly higher than in other fractions. For preferred sampling times, seasonal trends showed that concentrations of N, P, K, Ca, Na, S, Cu, and Fe were fairly stable over May-August. Similarly, concentrations of N, P, K, Ca, S, Zn, and Mn were relatively stable during December-February, after completion of the spring vegetative flush.

Somatic embryogenesis from leaf callus derived from mature trees of the cycad Ceratozamia hildae (Gymnospermae)

A friable and transient embryogenic callus was initiated from pinnae removed from leaves in new vegetative flushes of mature Ceratozamia hildae Landry & Wilson, a cycad. Somatic proembryos developed from the callus approximately 3 months after explanting onto plant growth medium consisting of a modified B5 formulation with 60 g l-1 sucrose, 400 mg l-1 glutamine, 100 mg l-1 arginine, 100 mg l-1 asparagine, 4.5 μM 2,4-dichlorophenoxyacetic acid with either 1.2 μM or 4.6 μM kinetin and 1.75 g l-1 gellan gum. Following subculture of somatic proembryos at this time onto medium without plant growth regulators, they continued to proliferate by a process resembling cleavage embryony or polyembryogenesis for several months. Proliferating embryogenic cultures consisted of hyperhydric somatic proembryos. Some 15 months after explanting, the somatic proembryos began to change in appearance; the suspensors became white and opaque, but were usually highly branched due to cleavage embryony. A single cotyledonary somatic embryo usually developed from the tip of each of the suspensors. Somatic embryos were primarily dicotyledonous, and less frequently monocotyledonous. Fewer than 10% of the somatic embryos appeared to be morphologically abnormal. Germination occurred in vitro whereby the coleorhiza elongated and a tap root emerged; however, plantlet recovery has not been demonstrated because the shoot axis failed to elongate.

Relationship between vegetative flushing and flowering of Macadamia integrifolia in Hawaii

Flowering patterns of the macadamia cultivars, ‘Kau’ (HAES 344), ‘Keaau’ (HAES 660), and ‘Kakea’ (HAES 508) were studied over three consecutive seasons at an orchard near Hilo, HI (elevation 27.4 m). These studies showed that all cultivars had broad flowering peaks with maximum anthesis occurring between January and April. The frequency of vegetative flushing was monitored during 1988, and raceme production by the flushes was observed during the subsequent flowering seasons (1988–1989, 1989–1990, 1990–1991, 1991–1992). Vegetative flushing occurred throughout the year for all cultivars but was more prominent during fall which coincided with the period of nut maturation. Sporadic flowering was observed within 1 year after vegetative flush emergence. For all cultivars, flowering of the 1988 flushes increased in 1989–1990, was most abundant in 1990–1991, and decreased in the 1991–1992 flowering season. Most racemes produced during 1989–1992 developed on flushes that were produced in the spring and fall of 1988.