Vegetative Bud Burst Research Articles

Crop Regulation Studies in guava (Psidium guajava L.) cv. L 49 under Ultra High Density Planting

A field experiment was carried out on 8 years old guava cv L 49 trees to assess the effect of pruning level and growth regulators with different combinations on vegetative growth and fruiting attributes in Ultra High Density Planting. The experiment consisted of 2 factors with 36 combinations viz., factor -1 (pruning level) P1- pruning of 25 cm of the shoot from the tip, P2- pruning of 50 cm of the shoot from the tip, P3- pruning of 75 cm of the shoot from the tip, P4 – control (without pruning). Factor -2(growth regulators) G1, G2- Potassium nitrate (1 ,2%), G3, G4- Thiourea (0.1 ,0.2%), G5, G6- Ethephon (250, 500 ppm), G7, G8- Cycocel (250, 500 ppm) and G9 – Control. Results showed that among different levels of pruning, 50cm pruning from the tip with potassium nitrate spray at 2 different concentrations was found to be the best for promoting early vegetative bud burst, fruit set and fruit yield. The increment in plant height and canopy spread in East-West and North-South were recorded more in 25 cm pruning from the tip. A greater number of shoots are visible in the P3G5 combination. When compared to other treatments, the P3G2 combination significantly increased the average index number of bud bursts and shoot length under Ultra High Density Planting.

Effect of grafting on phenology, susceptibility to Phytophthora cinnamomi and hormone profile of chestnut

Ink disease caused by the root-rot pathogen P. cinnamomi (Pc) threatens European sweet chestnut (Castanea sativa Mill.) orchards, and growers increasingly graft susceptible C. sativa traditional varieties on Pc-resistant hybrid commercial rootstocks. The influence of the scion, the rootstock, and grafting per se on the vegetative budburst, growth, susceptibility to Pc and defence-related hormone profile of Castanea spp. are unknown. In a greenhouse experiment, these effects were evaluated by reciprocally grafting two Pc resistant C. crenata x C. sativa clones and two Pc susceptible C. sativa clones. Resistance to Pc and the hormone content of leaves and roots were rootstock-dependent, and survival rates of susceptible chestnuts strongly increased when grafted on resistant rootstocks. The scion had no effect on the resistance to Pc and the hormone profile of leaves and roots of grafted trees, but influenced vegetative budburst and primary growth. Grafting per se increased susceptibility to Pc and altered the defence-related phytohormone content of trees, especially in resistant rootstocks, but did not influence budburst and growth of trees. Grafting-induced alteration of the constitutive defense-related hormone profile could explain the increased susceptibility of resistant rootstocks to Pc. Nine days after infection, a dynamic hormonal response consisting of decreased jasmonates (JA and JA-Ile) in leaves and increased ABA and JA-Ile in roots was observed in resistant chestnuts. This is the first study addressing the role of grafting in modulating resistance to the soil-borne pathogen Pc in chestnut trees.

Olive Bud Dormancy Release Dynamics and Validation of Using Cuttings to Determine Chilling Requirement.

Dormancy release dynamics in olive tree (Olea europaea L.) reproductive buds as affected by cold accumulation, tree bearing status, and budburst temperature was studied under natural and controlled conditions, using both cuttings and container- and field-grown plants. The chilling necessary for dormancy release was acquired at different times within the bud population, presenting a progressive pattern of reproductive budburst. Once sufficient chilling is accumulated, 20 °C is a suitable temperature for reproductive budburst, although higher temperature, e.g., 30 °C, during dormancy release can inhibit budburst. While the bearing status of trees determined the amount of return bloom, dormancy release followed a similar pattern for previously bearing and non-bearing trees. Concurrent with investigating budburst factors, the use of shoot cuttings was tested as a method for olive dormancy release studies by contrasting with results from whole trees. It was found it to be valid for studying reproductive budburst, thus providing a useful method to screen chilling requirements in cultivar evaluation and the breeding programs currently ongoing in this species. However, the method was not valid for vegetative budburst, with varying results between cuttings and the whole plant.

Experiments Are Necessary in Process-Based Tree Phenology Modelling.

In boreal and temperate trees, air temperature is a major environmental factor regulating the timing of spring phenological events, such as vegetative bud burst, through underlying physiological processes. This has been established by experimental research, and mathematical process-based tree phenology models have been developed based on the results. The models have often been applied when assessing the effects of climate change. Currently, there is an increasing trend to develop process-based tree phenology models using only observational phenological records from natural conditions. We point out that this method runs a high risk of producing models that do not simulate the real physiological processes in the trees and discuss experimental designs facilitating the development of biologically realistic process-based models for tree spring phenology.

Effectiveness of winter temperatures for satisfying chilling requirements for reproductive budburst of red alder (Alnus rubra).

BackgroundExperiencing an adequate amount of cold temperatures over winter is necessary for many temperate tree species to break dormancy and flower in spring. Thus, changes in winter and spring temperatures associated with climate change may influence when trees break dormancy and flower in the future. There have been several experimental studies that have quantified the effectiveness of cold temperatures for chilling requirements for vegetative budburst of temperate trees; however, there are few experimental studies addressing the chilling requirements for reproductive budburst of trees, as it is difficult to place reproductively mature trees in temperature-controlled environments.MethodsTo identify how changing temperatures associated with climate change may impact reproductive phenology, we completed a temperature-controlled growth chamber experiment using cuttings of reproductive branches of red alder (Alnus rubra), one of the most widespread hardwood tree species of the Pacific Northwest, USA. The purpose of this study was to examine how colder (4 °C) and warmer (9 °C) winter temperature regimes influenced the timing of reproductive budburst of red alder cuttings in spring. We also compared the date of budburst of cuttings to that of branches from intact trees.ResultsWe found that cuttings flowered earlier after pretreatment with a 4 °C winter temperature regime than after a 9 °C winter temperature regime. We found no significant differences between the timing of male budburst of cuttings exposed to ambient conditions compared to male budburst of branches from intact trees. We used our experimental data to estimate a “possibility-line” that shows the accumulated chilling and forcing temperatures necessary prior to reproductive budburst of red alder.DiscussionThis study provides a preliminary indication that warmer winters with climate change may not be as effective as colder winters for satisfying chilling temperature requirements of a Northwest hardwood tree species.

Chilling accumulation, dormancy release temperature, and the role of leaves in olive reproductive budburst: Evaluation using shoot explants

Abstract Winter rest and release of axillary buds from dormancy have been frequently noted but scarcely studied systematically in the olive tree (Olea europaea L). A series of experiments was carried out over three consecutive fall-winter periods, with one-node and three-node leafy and defoliated explants from shoots sampled from nonbearing (OFF) and bearing (ON) trees and forced in a growth chamber at different constant temperatures (12.5, 15, 20 and 30 °C). Buds acquired reproductive budburst capacity after a period of chilling accumulation on the tree for both OFF and ON explants, with percentage of reproductive budburst substantially higher in the OFF explants. Reproductive budburst occurred on explants sampled from early January to the second half of February, with slight variation in dates among the different experiments and seasons. During this period, forcing temperatures and defoliation influenced bud growth and development. Reproductive budburst activity indicated that 12.5 °C forcing temperature added effective chilling and promoted earlier budburst, while 20 °C forcing was only effective in promoting reproductive budburst after buds had accumulated enough natural chilling and 30 °C forcing produced a delay in reproductive budburst. From early sampling dates defoliation promoted vegetative budburst, which was then substituted by reproductive budburst as natural chilling accumulation increased. In histological comparisons of the buds a “shell-zone” of active morphogenetic activity was observed in the third node axils of OFF buds at the start of reproductive budburst capacity, later forming an inflorescence branch by the end of the sampling period. Starch presence shown by staining increased during the natural chilling accumulation period and then progressively disappeared with reproductive budburst. These results indicate dormancy release in the potentially reproductive buds following chilling and prior to inflorescence initiation and development. In addition to the developmental information they provide, the results permit standardizing the protocol to determine the period of dormancy release in olive tree reproductive buds.

The timing of flowering in Douglas-fir is determined by cool-season temperatures and genetic variation

Abstract Trees have evolved to time flowering to maximize outcrossing, minimize exposure to damaging frosts, and synchronize development with soil moisture and nutrient availability. Understanding the environmental cues that influence the timing of reproductive budburst will be important for predicting how flowering phenology of trees will change with a changing climate, and aid in the time-sensitive management of seed orchards. We examined how temperature influenced the timing of female flowering of coastal Douglas-fir with over 4500 flowering observations of trees from 12 sites across western Oregon and Washington. We predicted flowering dates by modifying chilling and forcing effectiveness functions from a model of vegetative budburst of Douglas-fir. We also examined whether genetic variation in Douglas-fir influenced the relationships between chilling and forcing accumulations using flowering observations from two common-garden experiments with trees from 60 populations from a diverse range of climates. Our reproductive budburst model predicted the day of flowering within an average of five days of the observed flowering dates across all sites and years. Fewer hours of forcing temperatures were required for flowering on sites that had experienced high chilling. Warmer temperatures in the future will likely result in earlier flowering on sites which currently have high chilling; however, sites which currently experience low chilling may display no change or possibly even a delay in flowering. Douglas-fir genotypes from different geographic regions flowered in the same order from year to year in common gardens, indicating that both temperature and genetic variation influence flowering. Genetic variation in flowering dates was more strongly related to summer drought of seed source locations than to cold winters. Knowledge of the environmental cues and genetic variation in timing of flowering can help predict how future changes in temperature under various climate models could change flowering time across the range of coastal Douglas-fir.

Grafting technique and rootstock species for the propagation of Plinia cauliflora

ABSTRACT: One of the biggest challenges for expansion of jabuticaba fruit tree cultivation is the high cost of seedlings due to to difficulties with vegetative propagation. Here, we aimed to evaluate graft survival in combinations of Plinia cauliflora and rootstocks of other species from the Myrtaceae family. The study was carried out at the Universidade Tecnológica Federal do Paraná - Campus Dois Vizinhos, Paraná State, Brazil. Eugenia uniflora L., E. involucrata DC, and P. cauliflora were used as rootstocks and were obtained as seeds. The 'whip-and- tongue' and cleft grafting techniques were tested for vegetative propagation. Grafted plants were cultivated in a greenhouse. The experimental design was a randomized complete block, in factorial 3×2 (rootstock species× graft type), with four replicates of 10 grafts by plot. Compatibility between rootstock species and scion was evaluated by diameter growth below and above the grafting point and by vegetative budburst and survival percentages. The use of P. cauliflora grafts with the same species was required for propagation. E. involucrata and E. uniflora rootstocks were not capable of propagation with P. cauliflora . Therefore, it is necessary to test other species from the Myrtaceae family.

Simultaneous down-regulation of DORMANCY-ASSOCIATED MADS-box6 and SOC1 during dormancy release in Japanese apricot (Prunus mume) flower buds

ABSTRACTIn temperate deciduous fruit crops such as Prunus spp., bud endodormancy is an important physiological phase affecting the timing of blooming and subsequent fruit development. Japanese apricot (Prunus mume) bears unmixed flower buds, separate from vegetative buds, that bloom slightly more than a month before vegetative bud burst. Seasonal expression of Prunus mume DORMANCY ASSOCIATED MADS-box genes (PmDAMs) has previously been analyzed only in vegetative buds, with an association between these genes and flower bud endodormancy release not yet confirmed. In this study, we performed a seasonal expression analysis of PmDAM1–6 genes in flower buds of two Japanese apricot genotypes – namely, high-chill and low-chill cultivars. The analysis revealed that PmDAM3, PmDAM5, and PmDAM6 expressions are closely associated with dormancy release in both flower and vegetative buds. In addition, a yeast two-hybrid screening demonstrated that PmDAM6 can interact in yeast with the homolog of Arabidopsis SOC1 (PmSOC1). Synchronized expression patterns were detected in PmDAM6 and PmSOC1 during dormancy release in flower buds of the two genotypes. Taken together, these results suggest that the dimer of PmDAM6 and PmSOC1 may play a role in the regulation of dormancy transition and blooming time in Japanese apricot flower buds.

Significance of the root connection on the dormancy release and vegetative bud burst of Norway spruce (<i>Picea abies</i>) seedlings in relation to accumulated chilling

The effect of cutting the root connection by detaching the shoot from the root system on dormancy release and vegetative bud burst was examined in 2-year-old seedlings of Norway spruce ( [L.] Karst.). Seedlings were transferred at 1–4 week intervals between October and January from outdoor conditions to experimental forcing in a heated greenhouse. Before forcing, half of the seedlings were cut above ground line, and the detached shoots were forced with their cut ends placed in water. The intact seedlings were forced with their root system remaining intact in the pots. Vegetative bud burst was observed visually. Cutting the root connection slightly increased days to bud burst in the forcing conditions, however, no consistent effect on bud burst percentage was found. Our preliminary seedling data suggest that using detached tree material in dormancy release experiments may have a small effect on bud burst date but it will evidently not lead to drastically erroneous conclusions. Further studies, using different seed lots, are needed to assess the effect of detaching on the dormancy release and bud burst, especially in adult trees.Picea abies

Dormant season fertigation promotes photosynthesis, growth, and flowering of ‘Blueshower’ rabbiteye blueberry in warm climates

In the subtropical lowland of Taiwan with a warm winter climate, most rabbiteye blueberry cultivars (Vaccinium ashei) are semi-deciduous, and their leaves remain green through the winter. We investigated whether fertigation with nitrogen (N) and phosphorus (P) during the dormant season had any subsequent effects on vegetative growth and flowering of rabbiteye blueberry in this region. Potted 3-year-old ‘Blueshower’ plants were fertigated weekly from November 2012 to March 2013 with combinations of 100, 200, or 400 mg·L-1 N and 200 or 400 mg·L-1 P. Plants fertigated without N and P served as the control. Fertigation with any N and P treatment during the dormant season significantly increased photosynthesis (Pn) of overwintered leaves relative to the control, but had no effect on Pn of the new leaves. N at 100 mg·L-1 increased the total chlorophyll content in overwintered leaves more than two-fold compared to the control; total chlorophyll content in overwintered leaves increased with N rate, but was not affected by P rate. Dormant-season N and P fertigation advanced vegetative budburst. However, new shoot growth was negatively affected by dormant-season P fertigation. The number of flowers increased with N rate. We concluded that in the subtropical lowland with a warm winter climate, dormant-season fertigations, especially to supply N, can improve flowering and canopy development in the following spring.

Genetic variation and heritability estimates of Ulmus minor and Ulmus pumila hybrids for budburst, growth and tolerance to Ophiostoma novo-ulmi

Seedlings obtained by crossing Ulmus minor and U. minor × U. pumila clones were assessed for flowering, bark beetle damage, vegetative budburst, height growth and resistance to Ophiostoma novo-ulmi. Ramets and open pollinated seedlings obtained from the parent trees were assessed for the same traits. Most progenies had similar traits to their parents, but some presented heterosis in annual growth or resistance to O. novo-ulmi. Leaf wilting was significantly lower in progenies with U. minor × U. pumila rather than U. minor as female parent (21.5 and 30.6%, respectively; P<0.05). Resistance to O. novo-ulmi increased significantly as a function of increased amounts of U. pumila germplasm from the female parent, suggesting that resistance to Dutch elm disease is primarily transmitted from the mother. Budburst occurred earlier in seedlings with low rather than high growth rates (P=0.0007) and percentage of wilting was negatively related to early budburst (P<0.0001). Other phenotypic relations included percentage of flowering trees and annual height growth (rp=0.44; P=0.0042), percentage of flowering trees and vegetative budburst (rp=-0.53; P=0.0004) and percentage of beetle-affected trees and annual height growth (rp=0.60; P<0.0001). Heritability estimates obtained from the regression and variance components methods ranged from 0.06 ± 0.04 to 0.64 ± 0.18, 0.10 ± 0.05 to 0.69 ± 0.17, and 0.13 ± 0.32 to 0.71 ± 0.22 for budburst, growth and tolerance to O. novo-ulmi, respectively. Broad- and narrow-sense heritability values were higher when estimated 60 days post inoculation (dpi) than 15, 30 or 120 dpi. Heritability estimates and genetic gains reported indicate a high degree of additive genetic control and show the effectiveness of selection for Dutch elm disease resistance and rapid tree growth.

A unigene set for European beech (Fagus sylvatica L.) and its use to decipher the molecular mechanisms involved in dormancy regulation.

Systematic sequencing is the method of choice for generating genomic resources for molecular marker development and candidate gene identification in nonmodel species. We generated 47,357 Sanger ESTs and 2.2M Roche-454 reads from five cDNA libraries for European beech (Fagus sylvatica L.). This tree species of high ecological and economic value in Europe is among the most representative trees of deciduous broadleaf forests. The sequences generated were assembled into 21,057 contigs with MIRA software. Functional annotations were obtained for 85% of these contigs, from the proteomes of four plant species, Swissprot accessions and the Gene Ontology database. We were able to identify 28,079 in silico SNPs for future marker development. Moreover, RNAseq and qPCR approaches identified genes and gene networks regulated differentially between two critical phenological stages preceding vegetative bud burst (the quiescent and swelling buds stages). According to climatic model-based projection, some European beech populations may be endangered, particularly at the southern and eastern edges of the European distribution range, which are strongly affected by current climate change. This first genomic resource for the genus Fagus should facilitate the identification of key genes for beech adaptation and management strategies for preserving beech adaptability.

A Phenology of Plants Distributed Near the Wind-holes in Jeongseon, South Korea

This study investigated the phenological phases of plant thorough monitoring the phenology of plants between October 15, 2009 and November 20, 2012. The phenological phases were observed at wind-holes at Yeotan-ri in Jeongseon-eup and Unchi-ri in Sindong-eup, Gangwon-do, with regard to vegetative bud burst, leaf out flowering, autumn leaves, and fallen leaves. The vegetative bud burst of Prunus choreiana H. T. Im was initiated on April 2, 2010 and it was bursted on April 16 in 2011 and April 19 in 2012. Its leaf out was started on April 23 (2010), May 11 (2011), and April 24 (2012). The autumn leaves was started to be observed on September 5 in 2012. The leaves began to fall on September 20 in 2012. The vegetative bud burst of Forsythia saxatilis (Nakai) was initiated on the same date as Prunus choreiana H. T. Im. The leaf development was observed on April 23 in 2010. In 2011, however, it was observed six days later (April 29) than the previous year. Moreover, it began to change into autumn leaves on October 22 in 2010. The autumn leaves began to fall on November 18 in the same year. No autumn leaves were observed in 2011, but they began to fall on November 8. Additionally, it began to change to autumn leaves on September 20 in 2012 and to fall on October 22. Given that the phenological monitoring of plants in wind-holes of the research sites is consistently conducted in the long term, the difference of phenology of plants in wind-holes for climate changes can be apparently determined.

Transcriptional profiling of bud dormancy induction and release in oak by next-generation sequencing

BackgroundIn temperate regions, the time lag between vegetative bud burst and bud set determines the duration of the growing season of trees (i.e. the duration of wood biomass production). Dormancy, the period during which the plant is not growing, allows trees to avoid cold injury resulting from exposure to low temperatures. An understanding of the molecular machinery controlling the shift between these two phenological states is of key importance in the context of climatic change. The objective of this study was to identify genes upregulated during endo- and ecodormancy, the two main stages of bud dormancy. Sessile oak is a widely distributed European white oak species. A forcing test on young trees was first carried out to identify the period most likely to correspond to these two stages. Total RNA was then extracted from apical buds displaying endo- and ecodormancy. This RNA was used for the generation of cDNA libraries, and in-depth transcriptome characterization was performed with 454 FLX pyrosequencing technology.ResultsPyrosequencing produced a total of 495,915 reads. The data were cleaned, duplicated reads removed, and sequences were mapped onto the oak UniGene data. Digital gene expression analysis was performed, with both R statistics and the R-Bioconductor packages (edgeR and DESeq), on 6,471 contigs with read numbers ≥ 5 within any contigs. The number of sequences displaying significant differences in expression level (read abundance) between endo- and ecodormancy conditions ranged from 75 to 161, depending on the algorithm used. 13 genes displaying significant differences between conditions were selected for further analysis, and 11 of these genes, including those for glutathione-S-transferase (GST) and dehydrin xero2 (XERO2) were validated by quantitative PCR.ConclusionsThe identification and functional annotation of differentially expressed genes involved in the “response to abscisic acid”, “response to cold stress” and “response to oxidative stress” categories constitutes a major step towards characterization of the molecular network underlying vegetative bud dormancy, an important life history trait of long-lived organisms.

Nitrogen deficiency increases basal branching and modifies visual quality of the rose bushes

Rosebush architecture resulting from the spatial organisation of the plant axes induces plant shape and consequently within ornamental horticulture context, its visual quality and commercial value. This architecture can be modulated by environmental conditions, particularly in the horticulture context in which the possibilities to control growing conditions are numerous. The objectives of the study were to determine, in young rose bushes, (1) whether short periods of nitrogen deficiency affect branching and (2) whether this effect is sufficient to modify the visual quality of the plant in a sustainable manner. Between vegetative bud burst and the petal colour visible stage of the generated primary branch, young rooted cuttings of bush rose (cv Radrazz) were subjected to one of three nitrogen regimes: (1) no nitrogen deficiency, (2) continuous nitrogen deficiency, i.e. 35 days of N deficiency, and (3) nitrogen deficiency restricted to the flowering stages, i.e. 18 days of N deficiency. After the petal colour visible stage, all three groups of plants were supplied continuously with nitrogen. We observed the morphology of the axes and the kinetics of axillary bud burst. Twelve weeks after the petal colour visible stage, the visual quality of the rose bushes was evaluated by an expert jury. We found that nitrogen deficiencies (1) increased bud burst ratios in the medial and basal zones of the primary branch, (2) delayed the bud burst in the apical zone of the primary branch and (3) had long-term effects on plant visual quality. The continuous nitrogen deficiency regime produced flatter, more asymmetric and less vigorous rose bushes than the no nitrogen deficiency regime. By contrast, nitrogen deficiency during the flowering stages only resulted in more symmetric, taller and more vigorous rose bushes than the no nitrogen deficiency regime. Based on these results, the role of nitrogen on bud burst was discussed and candidate processes at the origin of the visual quality modification were suggested. This new approach combining ecophysiology and sensory assessment of ornamental plants enabled the identification of some early architecture components to be correlated with later visual quality characteristics and then to better target the physiological processes of interest.

Effect of timing and concentration of rest breaking agents on budburst in ‘Bing’ sweet cherry under conditions of inadequate winter chilling in South Africa

The effect of timing of various rest breaking agents (RBAs) on vegetative and floral budburst, and production efficiency was investigated on 4-year-old ‘Bing’ sweet cherry trees on ‘Gisela® 5’ rootstock. Two experiments were conducted, near Clarens (28°28’S; 28°19’E, 1860 m.a.s.l) and Reitz (28°0’S; 28°28’E; 1717 m.a.s.l) in the eastern Free State, during 2005 and 2006, respectively. The 2005 experiment evaluated five treatments; 1% and 2% Dormex® (49% hydrogen cyanamide, HCN); 1% Dormex® + 3% Budbreak® oil (869.3 g L−1 mineral oil); and 3% Lift® (thidiazuron and mineral oil) sprayed on whole trees on three dates preceding expected “green-tip”, and an unsprayed control. In 2006 four treatments were evaluated; 1% Dormex®; 1% Dormex® + 3% Bud-break® oil (869.3 g L−1 mineral oil); 3% Lift® applied on three dates, and an unsprayed control. Compared to the control, RBAs were most effective at improving vegetative budburst during both seasons while results of floral budburst and production efficiency varied between seasons indicating that time of RBA application should be based on chilling accumulation and bud development stage and not only calendar date. The time of application of RBAs had the most significant influence on budburst and production efficiency. No interaction was observed between time and treatment.

Cone enhancement in Abies amabilis using GA 4/7, fertilizer, girdling and tenting

The demand for Abies amabilis (Dougl. Ex Loud) Dougl. Ex Forbes, Pacific silver fir seed has increased in British Columbia in recent years but the supply of wild seed is limited due to periodic cone crops and difficulty and high cost of cone harvest. Several clonal seed orchards have been established but cone production is very low. A study was undertaken to enhance cone production in a clonal seed orchard grafted in 1984. Five treatments were applied with 20 trees per treatment. Treatments began on 20 May 1998. Each tree was given two applications of GA 4/7 at 1 week interval, 20 and 27 May (early application) or 27 May and 3 June (late application). Ramets in treatment 2 received early GA 4/7 application+ fertilizer+ girdling . Ramets in treatment 3 received a similar treatment but given late. Ramets in treatment 4 received early GA 4/7 application+ fertilizer+ girdling+ tenting . Ramets in treatment 5 received a similar treatment but given late. Ramets in treatment 1 received one injection of 80% ethanol but no GA 4/7 on 30 May. Each treatment had 10 trees in which vegetative bud burst was early and 10 trees in which bud burst was late. Pollen and seed cone abundance was measured in April 1999. Only 10% of control ramets produced seed cones (0.75 cones/ramet). In treatment 2, 45% of ramets produced seed cones (8.4 cones/ramet). In treatment 3, 35% of ramets produced seed cones (2.3 cones/ramet). In treatment 4, 70% of ramets produced seed cones (23.1 cones/ramet). In treatment 5, 75% of ramets produced seed cones (21.2 cones/ramet). Pollen cone enhancement was statistically significant for treatments 2–5 over controls but production was not as dramatic as for seed cones because most control ramets produced some pollen cones.

Budburst and yield of ‘Peeka’ apricot influenced by time and concentration of hydrogen cyanamide application

The rest-breaking response of ‘Peeka’ apricots (P. armeniaca L.) grown locally under conditions of inadequate winter chilling to 0%, 0.25%, 0.5%, 0.75%, and 1% hydrogen cyanamide sprayed 29 July, 3 August, 13 August, and 17 August 1987 is reported, owing to renewed interest in this chemical following the recent withdrawal of dintro-ortho-cresol (DNOC). These dates ranged from ca. 7 to 4 weeks before reproductive budburst of the control (15 September), and covered the perceived optimum spray period. Vegetative budburst increased with rate and time of hydrogen cyanamide application and was highest with 0.75% hydrogen cyanamide sprayed on 13 August. Reproductive budburst also increased with rate reaching a maximum with the 13 August applications. Yield increased with rate up to 1% hydrogen cyanamide and was also time dependent. Highest yield was obtained with the 3 August application, one week earlier than the optimum date for budburst on 13 August. These results from one season confirm the occasional observation of disappointing fruit set following intense blossom after the application of hydrogen cyanamide. Additional data are required to predict application dates to optimise fruit set.

Analysis of genetic variation for quantitative characters between and within four native populations of scots pine (Pinus sylvestris)

Summary A combined provenance/progeny trial of native Pinus sylvestris populations was established on a site in southern Scotland in 1991. Four provenances (Abernethy, Glen Affric, Loch Maree and Rannoch) were chosen to represent the range-wide geographical variation for this species within Scotland. At three years after outplanting (7 years of age) the quantitative traits of spring vegetative bud burst, height and diameter were measured. Significant genetic variation was detected among provenances for most of the quantitative traits analysed. Glen Affric provenance showed poor height and diameter growth, while Abernethy provenance burst its buds approximately one week later than the remaining provenances. For the morphological traits measured a genetic basis for within provenance variation was demonstrated. The coefficient of genetic variation (CG) and heritability estimates (h2) suggest that the genetic resource for growth traits within populations is still high (CG = 9.3–16.7%). In contrast the populat...