Terminal Bud Set Research Articles

Diallel crosses in Picea abies III. Variation and inheritance patterns in nursery trials

Abstract The complete diallel cross is the only mating design that provides estimates of variance components of general combining (GCA), specific combining ability (SCA), maternal and reciprocal effects, in addition to heritabilities and genetic correlations. To obtain such estimates, complete diallels were made among 10 trees in each of three natural Norway spruce populations from altitude 300 and 500 m in Norway. Nursery trials were performed with the families from these crosses and families from seeds collected from open pollination. Traits measured and analysed are seed weight, germination rate, germination percentage, terminal bud set, and seedling heights the first and second years. The seedlings from the population at origin 500 m had lower seed weight, lower heights and earlier bud set than those from the two populations from lower altitude. A considerable variation was present among families within each diallel, and the GCA variance components had the highest values and were significant for most traits. Variance components for SCA and maternal effects were also significant for some traits, but with inconsistent values in the three diallels. A strong relationship was present between the weight of the seed lots from the maternal parent and mean family height after one and two growing seasons. The highest estimate of heritability was observed for bud set, with similar values in all three diallels.

Interspecific morphological variation in Juglandoideae resting bud organization: a winter's tale?

Dormant resting buds are frequently regarded as static units, with protective cataphylls on the outside and embryonic foliage leaves on the inside. How the presence of cataphylls influences the dynamic, cyclical, annually repeating sequence of leaf forms that a resting bud gives rise to has rarely been interrogated. To examine the connection between dormant structure and growing-season development, we compare the complete seasonal heteroblastic sequence of leaf forms of six species of temperate Juglandaceae with distinctly different vegetative resting bud structures. These include buds with cataphylls; buds without cataphylls; and buds with caducous cataphylls that are lost before the onset of winter. In a common garden setting over a 7-month growing season, the dimensions of 2249 individual vegetative metamers were tracked from first exposure to abscission along the shoots of saplings and mature trees. The timing of metamer initiation within terminal buds was investigated using micro-CT scanning. Character state transitions of resting bud types were estimated using a phylogenetic tree of Juglandaceae. The presence of cataphylls within a heteroblastic sequence is associated with a single cohort of foliage leaves that flush and abscise synchronously. This growing pattern is highly determinate, with next year's terminal-bud cataphylls already initiated before spring leaf out. In contrast, in sequences without cataphylls, shorter-lived foliage leaves appear and abscise in a staggered fashion. Despite these differences in leaf demography, all examined heteroblastic sequences produce a series of small, caducous leaf forms that precede terminal bud set. The ubiquity of caducous leaf forms in Juglandoideae may point to the importance of shoot tip protection far beyond the dormant season. In addition, the presence or absence of cataphylls in resting buds is indicative of distinct shoot ontogenetic patterns, and functional strategies, in summer.

Epigenetic memory effects in Norway spruce: are they present after the age of two years?

ABSTRACT Short-term trials on cultivated soil were planted with families of Norway spruce that had shown epigenetic memory effects in early tests up to age two years. Measurements and assessments were made of phenology traits, tree heights and stem defects until age 16 years in these trials. The memory effects of the temperature conditions during embryo development and seed maturation were confirmed for the timing of bud flush and for start and cessation of shoot elongation at age six years. The mean differences in timing of these events caused by temperature treatments were on average less than two days. They were considerably larger for families with strong effects on terminal bud set at the end of the first growing season. The memory effects did not result in a prolonged shoot growth period, nor did they affect height growth. Interaction effects expressed in adaptive traits between factorial treatments of temperature and daylength during seed production were large in the short-term trial and were still present at age nine years. The results presented demonstrate that strong memory effects observed in early tests may also be expressed in phenology traits for at least the next five growing seasons.

Assessing and Minimizing the Development and Spread of Fire Blight Following Mechanical Thinning and Pruning in Apple Orchards.

The adoption of mechanical thinning and pruning in commercial apple orchards has been limited largely by the risk of development and spread of fire blight. This devastating disease, caused by the bacterial pathogen Erwinia amylovora, may be transmitted by mechanical injury such as pruning, especially under warm, moist conditions conducive to bacterial growth, infection, and disease development. However, risk may be mitigated by avoiding highest-risk times and applying a bactericide, such as streptomycin, after mechanical thinning or pruning. In 'Gala' and 'Idared' orchards, we evaluated the risk of fire blight development and spread after mechanical thinning early in bloom (20% bloom), when seasonal temperatures are cooler and there are few open flowers available for infection. In both orchards, we also evaluated the spread and development of fire blight by mechanical pruning in July and in August, before and after terminal bud set, when shoot growth is slowed and the tree is less susceptible to infection. We also assessed the potential efficacy of a streptomycin or Bacillus subtilis biopesticide application after mechanical thinning and pruning to mitigate the spread of fire blight. In the 'Gala' orchard, disease never developed beyond the inoculated tree after thinning or pruning, which was unexpected for this highly susceptible cultivar. In the 'Idared' orchard, incidence of blossom or shoot blight from the point source, represented as relative area under the disease progress curve, was rarely different for trees that underwent mechanical thinning or mechanical pruning compared with untreated trees, and it was often reduced or eliminated when the antibiotic streptomycin or the B. subtilis biopesticide was applied within 24 h of mechanical thinning or pruning. For both thinning and pruning, incidence of fire blight dropped off quickly beyond the inoculated tree in the 'Idared' orchard and generally was not observed in trees beyond 10 to 15 m from the inoculated point source or predicted beyond 10 m by exponential and power law models fit to the disease progress curves. The results of this work demonstrate the low risk for fire blight development and spread by mechanical thinning and pruning when practiced under low-risk conditions-early in bloom for mechanical thinning and after terminal bud set (in August) for mechanical pruning-especially when paired with a subsequent bactericide application. This study demonstrates the safe use of mechanical thinning and pruning in commercial apple production, corroborated by anecdotal evidence from apple growers in western New York State.

Adaptive performance of genetically improved and unimproved seedlings of Scots pine

Our main objective was to determine whether various genetically improved reproductive materials of Scots pine ( L.) differ in growth rhythm, autumn cold acclimation and resilience from unimproved materials. The study consisted of two successive indoor experiments with Scots pine seedlings representing four levels of genetic gain (unimproved natural stands, first-generation seed orchards, 1.5-generation seed orchards and seed orchards established with freezing-tested parents) and a wide range of geographical origins within Finland. The seedlings were assessed for terminal shoot elongation, growth cessation, bud set, freezing injuries and bud flushing over the first growth period. All the adaptive traits showed a latitudinal trend regardless of the genetic level. Seed orchard progenies and natural stand progenies did not differ significantly in the timing of growth cessation, bud set, and the flushing rate of the frost-injured seedlings, after the trait variation was adjusted to the latitude of origin. The differences in autumn frost hardiness were insignificant, too, except for the somewhat higher injury rate displayed by the first-generation seed orchard materials. The finding was not conclusive due to ambiguous results from the two experiments. Overall, we did not find evidence of alarming compromises in the adaptive performance of genetically improved materials.Pinus sylvestris

Efficiency of night interruption treatments with red and far-red light-emitting diodes (LEDs) in preventing bud set in Norway spruce seedlings

Terminal bud set can be prevented by interrupting night with short pulses of light when the natural photoperiod is too short to maintain growth. Norway spruce (Picea abies Karst.) seedlings originating from 61°N and 64°N were grown in growth chambers under conditions that mimic growth conditions in a heated greenhouse in early spring in Finland (experiment 1) or under constant growth conditions (experiment 2). The seedlings were exposed to the following night interruption (NI) treatments using light-emitting diodes (LEDs) that generated red (R, peak at 660 nm) and far-red (FR, peak at 735 nm) wavelengths in 20 s pulses at 15 min intervals: (i) red light alone (R); (ii) R combined with FR (R + FR); and (iii) control (no NI treatment). The R + FR treatment was more effective in preventing terminal bud set than the R treatment. Seedling responses depended on the provenance and growth conditions. The R treatment reduced the proportion of seedlings with terminal buds in the 61°N seedlings and delayed bud set in the 64°N seedlings. The fluctuating growth conditions or longer dark period between the photoperiod and NI treatments reduced the efficiency of the R + FR treatment. A combination of R and FR LEDs with adequate light intensity and duration is suitable for intermittent NI treatment in Norway spruce seedlings.

Combined effects of short-day treatment and fall fertilization on growth, nutrient status, and spring bud break of Pinus tabulaeformis seedlings

Abstract: Although effects of short-day treatment and fall fertilization on seedling development have been studied independently, their combined influences are not well elucidated. We explored growth, nutrient concentration, and spring bud break of Chinese pine (Pinus tabulaeformis Carr.) seedlings exposed to two photoperiod treatments (short-day consisting of 3 weeks of 18-hr nights in late summer and ambient day length) and three rates of fall N fertilization (0, 12 and 24 mg N per seedling). Seedlings were assessed before fall fertilization and at the end of the growing season. Bud break timing was evaluated the following spring. Increased foliar P concentration concurrent with reduced root P and K concentration occurred in short-day treated seedlings at the conclusion of photoperiod treatment. By the end of the growing season, short-day treatment resulted in greater N and P concentration in the stems, and P concentration in the foliage. It also induced smaller foliage and stem dry mass in both stages. Fall fertilization consistently enhanced tissue N concentration, but interaction effects with short-day treatment were generally non-significant. Short-day treatment curtailed shoot growth, induced terminal bud set, and hastened spring bud break (by only one day) for this mid-latitude seed source (41° N). Thus, short-day treatment or fall fertilization each promoted an increased nutrient concentration, while having only a minor effect on spring bud break.

Growth and development of Norway spruce and Scots pine seedlings under different light spectra

The goal of this study was to examine how different light spectra affect growth and development of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) seedlings. The seedlings were grown in a darkened greenhouse under four light spectra consisting of different proportions of blue (B, 400–500nm), red (R, 600–700nm), and far-red (FR, 700–800nm) light, with high-pressure sodium lamps (HPS) serving as controls. The light treatments (250μmolm−2s−1 photosynthetically active radiation) were provided using light-emitting diodes (LEDs), and the treatments included the following: (1) 25% B+70% R+5% FR; (2) 25% B+75% R; (3) 55% B+45% R; and (4) HPS: 6% B+44% green (500–600nm)+41% R+9% FR. We measured germination, growth, morphology, gas exchange, N concentration in needles and stem, and terminal bud set of the seedlings after a 4-month growth period. Our results showed that the physiological and morphological responses of shade-intolerant Scots pine seedlings to light quality were more pronounced than those of the shade-tolerant Norway spruce seedlings. Growth under the FR-containing light treatments produced tall seedlings with larger needle dry mass. Removal of FR and addition of B in the growth light reduced the height growth, and it increased the sturdiness and altered the branching patterns in the seedlings. Growth under the treatment containing about 25% B and 75% R resulted in the highest root-to-shoot ratios in both species and highest root growth capacity and water-use efficiency in Scots pine. Timing of bud set was independent of growth light spectra. Our results show that it is possible to improve the seedling attributes that are contributing to good performance potential by using different wavelength combinations in growth light, particularly in Scots pine. However, the potential after-effects of growth under an incomplete light spectrum on seedling performance after planting to forest regeneration site are still unknown.

Verification of a phenotypic discrimination method for hybrid larch seedlings using DNA markers

The hybrid between Kuril larch (Larix gmelinii var. japonica) and Japanese larch (L. kaempferi) is an important afforestation tree species in Hokkaido, Japan, because of its rapid juvenile growth, straight stem, and resistance to bark gnawing by voles. To produce desirable hybrid seedlings, precise seedling discrimination is essential. However, continuous variations in morphological and phenological traits occur across L. gmelinii var. japonica × L. kaempferi and L. gmelinii var. japonica × L. gmelinii var. japonica seedlings. Therefore, we used DNA markers to verify and improve the morphological and phenological discrimination method. We collected seeds from an interspecific seed orchard and, using chloroplast DNA analysis, we showed that the hybridization rates of 1-year-old seedlings were different between years (2004, 23.2 %; 2005, 53.6 %) and between mother trees (2004, 5.8–39.4 %; 2005, 20.0–81.0 %). Discriminant analyses revealed that the root collar diameter of 2-year-old seedlings, number of sylleptic branches of 2-year-old seedlings, and day of terminal bud set in 1- and 2-year-old seedlings are traits that aid in discriminating hybrid seedlings. The proportions of correctly discriminated individuals were found to be 81.7–88.2 % when using improved phenotypic discrimination methods. These methods adopted traits with high discrimination abilities during discriminant analyses and determined the selection intensity according to the hybridization rate estimated from the DNA markers. In contrast, the proportions of correctly discriminated individuals obtained using the current method were lower, 72.7–78.5 %, because this method was based on seedling height and adopted a constant selection intensity.

Functional and Expressional Analyses of PmDAM Genes Associated with Endodormancy in Japanese Apricot

Bud endodormancy in woody plants plays an important role in their perennial growth cycles. We previously identified a MADS box gene, DORMANCY-ASSOCIATED MADS box6 (PmDAM6), expressed in the endodormant lateral buds of Japanese apricot (Prunus mume), as a candidate for the dormancy-controlling gene. In this study, we demonstrate the growth inhibitory functions of PmDAM6 by overexpressing it in transgenic poplar (Populus tremula × Populus tremuloides). Transgenic poplar plants constitutively expressing PmDAM6 showed growth cessation and terminal bud set under environmental conditions in which control transformants continued shoot tip growth, suggesting the growth inhibitory functions of PmDAM6. In the Japanese apricot genome, we identified six tandemly arrayed PmDAM genes (PmDAM1-PmDAM6) that conserve an amphiphilic repression motif, known to act as a repression domain, at the carboxyl-terminal end, suggesting that they all may act as transcriptional repressors. Seasonal expression analysis and cold treatment in autumn indicated that all PmDAMs were repressed during prolonged cold exposure and maintained at low levels until endodormancy release. Furthermore, PmDAM4 to PmDAM6 responses to a short period of cold exposure appeared to vary between low- and high-chill genotypes. In the high-chill genotype, a short period of cold exposure slightly increased PmDAM4 to PmDAM6 expression, while in the low-chill genotype, the same treatment repressed PmDAM4 to PmDAM6 expression. Furthermore, PmDAM4 to PmDAM6 expression was negatively correlated with endodormancy release. We here discuss the genotype-dependent seasonal expression patterns of PmDAMs in relation to their involvement in endodormancy and variation in chilling requirements.

Nutrient Accumulation and Flower Bud Formation Affected by the Time of Terminal Bud Set on Water Sprouts of Persimmon

Heavy pruning to lower tree height of persimmon results in excessive production of water sprouts and reduced yield. This experiment was conducted on ‘Fuyu’ (Diospyros kaki) trees to assess if the time for terminal bud set of water sprouts affected flower bud formation. Some sprouts were not pruned to serve as fruiting branches for the next season. Thirty to 40 water sprouts were tagged in 2005 and 2006, the growth of which stopped from mid-June to late August. The later terminal buds set, the lower the percent dry weight in the apical 10 cm. The apical segments of sprouts that continued to grow to mid- to late August were characterized by low soluble sugars, starch, and inorganic elements such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) compared with those that set terminal buds earlier. The number of flower buds from the water sprouts that set terminal buds by early August the previous year bore more than 12 flower buds the next year, whereas those that grew to mid- to late August bore fewer than three. It was concluded that water sprouts could be used as fruiting branches for the next year as long as terminal buds set by early August, thereby alleviating yield reductions that come with heavy pruning.

Tree Growth Stage and Environment After Pathogen Inoculation Alters Susceptibility of Pear Trees to Phytophthora Canker~!2009-11-17~!2010-01-01~!2010-04-29~!

We investigated whether pear (Pyrus communis L. OHF97) tree growth stage, nitrogen (N) status, wound age, and infection environment influences susceptibility to Phytophthora syringae Klebahn. Actively growing trees were sus- ceptible to the pathogen when inoculated before terminal budset and cooler temperatures increased disease severity. In the autumn, during early stages of dormancy development after budset there was no relationship between temperature after inoculation and susceptibility and as trees became more dormant a negative relationship developed between temperature and susceptibility. Altering tree N status in the autumn after budset by spraying leaves with urea had no influence on sus- ceptibility, regardless of environmental conditions after inoculation. Lesions developed when fresh wounds (0 d to 1 d old) were inoculated after budset, but as wounds aged they were less susceptible to infection. These results suggest a combination of tree growth stage when inoculated with the pathogen and environmental conditions afterward play impor- tant roles in disease development. Differences in susceptibility may be a direct result of temperature on pathogen activity or an indirect effect of temperature on tree metabolic activity. Differences in tree susceptibility related to dormancy devel- opment may be related to stem N status or the ability of trees to produce a barrier to infection after stems are wounded. Surface wounds inflicted during handling after budset may serve as infection locations for P syringae; however the length of time between wound formation and exposure to the pathogen dictates whether infection will occur when trees are in the early stages of dormancy development.

MANIPULATION OF THE ANNUAL GROWTH CYCLE OF BLUEBERRY USING PHOTOPERIOD

MANIPULATION OF THE ANNUAL GROWTH CYCLE OF BLUEBERRY USING PHOTOPERIOD

Method of Nitrogen Application in Summer Affects Plant Growth and Nitrogen Uptake in Autumn in Young Fuji/M.26 Apple Trees

Effects of foliar vs. soil nitrogen (N) application during the summer and the autumn were studied in young Fuji apple trees (Malus domestica Borkh) on Malling 26 (M.26) rootstock. One‐year‐old bench‐grafted trees were potted in 3.8‐liter pots in a mix of perlite, peat moss, and loam soil (1:1:1 by volume) and were treated weekly from late June to early September with 0.5% urea either by foliar or soil application or soil application of water (control). At the end of September, five trees from each treatment were harvested, and shoot and root growth and leaf N concentration were determined. In mid‐October of the same year, trees from each treatment were randomly divided into three subgroups. One group received soil application of water (control), and the other groups received either a foliar or soil application of 3% 15N‐urea. After natural leaf defoliation, trees were harvested, and total N and 15N concentration of stems (all aboveground tissue) and roots was determined. Regardless of application method, N application during the summer promoted plant growth and increased leaf N concentration. Soil N application during the summer stimulated more shoot and extension root growth than foliar N application. In contrast, the foliar N application in the summer promoted more feeder root growth than soil N application. Regardless of application method, autumn N application after terminal bud set had little effect on current‐year growth but increased total plant N concentration. In the autumn, trees that received soil N applications in the summer had more 15N uptake by leaves, while trees receiving foliar N applications in the summer had more 15N uptake by root. These results suggest that the differential influence of N application methods during the summer on growth and partitioning of trees affects tree responsiveness to autumn N applications. The use efficiency of autumn‐applied N depends on the method of N application in the summer.

Provenance variation in camptothecin concentrations of Camptotheca acuminata grown in China

Camptotheca acuminata, a deciduous tree indigenous to southern China, contains camptothecin (CPT), an alkaloid of anti-cancer properties. Eighteen provenances were collected across its native range in 10 provinces south of the Yangtze River. A provenance test was performed for one growing season. Both growth characteristics and leaf CPT concentrations were determined. Seasonal height growth followed a typical “S”-shaped pattern, with a negligible height increment in the beginning of the season, a slow growth period from June 27 to August 11, a rapid growth period, and in the end a gradual decline in height increment with terminal bud set in mid-October. Final stem heights varied significantly among the 18 provenances. The difference was 43 cm or 38% between the tallest and the shortest. Significant differences were found among the 18 provenances in biomass production of whole-plant, shoot, leaf, root, and bark after one year of growth in nursery settings. Leaf CPT concentrations exhibited three-fold difference among the 18 provenances. Leaves are to be used as the target plant material for extracting CPT and the top five provenances were identified. These provenances warrant further field testing to determine the optimal growth conditions for accumulation of CPT.

431 Seasonal Changes in Nitrogen Uptake Efficiency in a Woody Ornamental (Tilia cordata Mill. `Greenspire')

Fertilizer recommendations for woody ornamentals suggest applying nutrients in early spring at budbreak, and in fall at the time of leaf coloration or leaf abscission. Because plants lack functional leaves at those times, there would be minimal contributions from photosynthesis to active ion absorption or from transpiration to mass flow of ions in soil towards roots. Thus, we hypothesized that fertilizer efficiency also would be low at those times. To estimate N uptake efficiency, 15N-enriched fertilizer was applied to container linden trees at one of five times during the 1998 season: at budbreak, during active growth, after terminal bud-set, before leaf abscission, and during leaf abscission. Half of the plants received 15N-nitrate-enriched ammonium nitrate on each date, and half received 15N-ammonium-enriched ammonium nitrate. Treated plants were harvested 10 days after enriched fertilizer application (29 May, 6 July, 17 Aug., 28 Sept., and 16 Nov.). Patterns of uptake were not different between plants treated with 15N-ammonium- or 15N-nitrate-enriched fertilizer. In both cases, nitrogen recovery efficiencies at budbreak and leaf abscission were much lower than at other application times. Whole-plant recovery efficiency of 15N-nitrate-enriched ammonium nitrate was 10% at budbreak, 13% at leaf abscission, and ranged from 58% to 71% for the intervening times. Recovery of 15N-ammonium-enriched ammonium nitrate was 6% at budbreak, 24% at leaf abscission, and 42% to 56% for intervening times.

Effects of Nitrogen Cut-off Date in Combination with Urea or Abscisic Acid (ABA) on Terminal Bud Set, Defoliation, Cold Acclimation, and Reserve Nitrogen in `Gala' Apple Nursery Stock

Bench-grafted `Gala'/M26 apple trees were grown in pots and fertigated weekly with 150 ppm N starting from 10 May. N supply was terminated on 21 Aug., 18 Sept., and 9 Oct. for the early, mid, and late N cut-off treatment, respectively. Half of the trees in the early N cut-off treatment were sprayed twice with 3% urea at 6-day intervals in early October. Half of the trees in the mid and late N cut-off treatment were sprayed twice with 1000 ppm ABA at 5-day intervals in early and mid-October, respectively. Early N cut-off significantly enhanced terminal bud set, defoliation, and induction of cold acclimation compared to the late N cut-off. Foliar urea increased the reserve N level in all tissues of the early N cut-off trees, almost to the level of late N cut-off trees. Soluble protein concentrations were increased by foliar urea, which accounted for about 23%, 10%, and 17% of the increase in the total N concentration in bark, wood, and roots, respectively. ABA treatment enhanced leaf senescence and N mobilization in the mid and late N cut-off trees, but did not affect terminal bud set and cold hardiness.

The Influence of Drought on Growth and Gas Exchange in Fraxinus species

Fraxinus americana, F. pennsylvanica, and F. nigra were subjected to short-term drought of 4, 8, and 16 days. Seedlings were obtained from a commerical nursery and grown in 4:1 pine bark:sand media for 3 months prior to the onset of the stress. Seventy-two trees with six replicates per stress treatment were arranged in a completely randomized design. Following each stress period, the appropriate trees were well watering and monitored through recovery. Leaf photosynthesis, shoot growth, leaf emergence, terminal bud set, trunk caliper and soil moisture content were measured through the stress and recovery periods. Drought suppressed shoot growth and leaf emergence in all species; however, Green Ash maintain active growth at higher rates than either White or Black. Leaf photosynthesis was reduced in both White and Black following 4 days of drought whereas Green ash was not adversely effected until day 10. Trees were harvested following recovery and dry weight fractions of leaves, stems, and roots recorded.

Controlling Floral Initiation and Vegetative Growth of Apple with Prohexadione Calcium (BAS-125W), an Experimental GA-biosynthesis Inhibitor

Early fruit production and control of tree size are important factors in the economic viability of high-density apple orchards. A horticultural tool permitting growers to induce terminal budset should provide greater control over the balance between vegetative growth and reproduction, increasing orchard production and profitability. With this goal, the experimental GA-biosynthesis inhibitor, BAS-125W, is being evaluated for effects on enhancing floral initiation and controlling tree size in young orchards. In nursery stock, the effect of inducing earlier terminal budset is also being studied for influence on storage carbohydrates and performance after planting. Studies in 1996 showed that 250 ppm BAS-125W induced terminal bud set on actively growing second-leaf `Macoun', `Delicious', and `Fuji' trees. Seven application dates from 17 June to 9 Sept. were compared to determine how time of treatment would effect degree and distribution of flowering the following year. Terminal budset typically occurred 2 weeks after application, with shoot growth resuming in 4 to 5 weeks. At two dates, treatment of growing tips only was compared with entire tree application to distinguish the direct effect of GA-inhibition on floral initiation from the effect of redistributing photosynthate. Treatment from 17 June to 29 July significantly reduced total annual shoot growth compared to the untreated controls, while later treatments had no significant effect on shoot length. Treatments of nursery stock with BAS-125W on 1 Sept. accelerated terminal bud set by at least 7 days compared to untreated controls of both `Fuji' and `Golden Delicious'. Effects of treatments on flowering and tree growth in 1997 will be discussed.

Effect of Abscisic Acid on Nitrogen Mobilization, Dormancy, and Cold Acclimation in Apple Trees

Spring-grafted potted `Fuji'/M26 apple (Malus domestica Borkh.) trees were fertigated with Plantex (20N–10P–20K) weekly until 28 Aug., and sprayed with 1000 ppm abscisic Acid (ABA) two times at 5-day intervals in early September. Nitrogen concentrations of leaves, bark, wood, and root tissues were analyzed using near-infrared reflectance (NIR) spectroscopy at 20to 30-day intervals beginning in August. In general, during leaf senescence, the content of leaf nitrogen decreased and stem nitrogen increased. ABA enhanced leaf senescence and the mobilization of nitrogen from the leaves to the stem tissues. ABA significantly enhanced terminal bud set, endodormancy induction, and cold acclimation. Eventually, the controls attained the similar degree of nitrogen concentration in the stem, terminal bud set, endodormancy, and hardiness.