Leaf Bud Break Research Articles

Variation in Phenology of Banj Oak (Quercus Leucotrichophora) Tree Across Different Elevations in the Kumaun Himalayas, India.

Changes in phenological events have been caused by the present phenomenon of climate change. The elevation is another important factor which leads to the variations in phenological events. The Banj Oak plays holds a vital position as a keystone species in the moist temperate forests of the Central Himalayas, and contribute to human well-being by providing essential benefits such as biodiversity conservation, maintenance of soil organic matter, and the ability to retain water. Thus, this study aims to evaluate the various phenological events of Q. leucotrichophora tree species along the elevation gradients. The elevation gradients are low (1400-1600 m), mid (1700-1900 m) and high (2000-2200 m). At each elevation, three sites were selected for the detailed phenological study. The observations were made from bud initiation to seed fall. In general, leaf bud break and leaf fall were initiated earlier in low-elevation species. In comparison with the middle and high elevation, at low elevation the growth initiation occurred in February and March when the temperature had begun. Comparisons with previous studies have shown that some phenological events began to occur early. The study clearly indicates that climatic irregularities have influenced or altered the phenological events of species. It can be said that the phenological events changes with climatic factors, which are responsible for earlier or delayed phenophases. Understanding phenology and its variations can offer significant data. Consequently, this knowledge can be highly valuable for agricultural practices, which necessitate advanced information on particular stages of tree growth.

Peculiarity of transcriptional and H3K27me3 dynamics during peach bud dormancy

Bud dormancy facilitates the survival of meristems under harsh environmental conditions. To elucidate how molecular responses to chilling accumulation controlling dormancy in peach buds, chromatin immunoprecipitation sequencing to identify the H3K27me3 modifications and RNA sequencing of two peach cultivars with pronounced differences in chilling requirement were carried out, the results showed that genes associated with abscisic acid and gibberellic acid signal pathways play key roles in dormancy regulation. The results demonstrated that peach flower bud differentiation occurred continuously in both cultivars during chilling accumulation, which was correlated with the transcript abundance of key genes involved in phytohormone metabolism and flower bud development under adverse conditions. The more increased strength in high chilling-requirement cultivar along with the chilling accumulation at the genome-wide level. The function of the dormancy-associated MADS-box gene PpDAM6 was identified, which is involved in leaf bud break in peach and flower development in transgenic Nicotiana tabacum (NC89). In addition, PpDAM6 was positively regulated by PpCBF, and the genes of putative dormancy-related and associated with metabolic pathways were proposed. Taken together, these results constituted a theoretical basis for elucidating the regulation of peach bud dormancy transition.

Genotype accounts for intraspecific variation in the timing and duration of multiple, sequential life-cycle events in a willow species.

Phenological variation among individuals within populations is common and has a variety of ecological and evolutionary consequences, including forming the basis for population-level responses to environmental change. Although the timing of life-cycle events has genetic underpinnings, whether intraspecific variation in the duration of life-cycle events reflects genetic differences among individuals is poorly understood. We used a common garden experiment of 10 genotypes of Salix hookeriana (coastal willow) from northern California, USA to investigate the extent to which genetic variation explains intraspecific variation in the timing and duration of multiple, sequential life-cycle events: flowering, leaf budbreak, leaf expansion, fruiting, and fall leaf coloration. We used seven clones of each genotype, for a total of 70 individual trees. Genotype affected each sequential life-cycle event independently and explained on average 62% of the variation in the timing and duration of vegetative and reproductive life-cycle events. All events were significantly heritable. A single genotype tended to be 'early' or 'late' across life-cycle events, but there was no consistent response within genotypes for event durations. This research demonstrates that genetic variation can be a major component underlying intraspecific variation in the timing and duration of life-cycle events. It is often assumed that the environment affects durations, but we show that genetic factors also play a role. Because the timing and duration of events are independent of one another, our results suggest that the effects of environmental change on one event will not necessarily cascade to subsequent events. This article is protected by copyright. All rights reserved.

Significance to the Horticulture Industry

Significance to the Horticulture Industry

Quantification of 'Candidatus Phytoplasma prunorum' in apricot trees exhibiting uneven European stone fruit yellows symptoms

This study focused on quantification of 'Candidatus Phytoplasma prunorum' in apricot trees exhibiting uneven symptoms of European stone fruit yellows. For the research, 17 trees showing early leaf bud break in one part of the crown were selected in winter season, and 13 trees showing leafroll in older part of the shoots and no symptoms in younger part of the same shoots were selected in summer season. Absolute quantification of phytoplasmas was performed by real-time PCR in samples collected from asymptomatic and symptomatic parts. The results showed, that phytoplasma could not be always detected in asymptomatic parts, where 2 out of 17 samples from asymptomatic parts from winter season were negative while in summer season 6 out of 13 samples from asymptomatic parts were negative. Comparison of phytoplasma quantities between symptomatic and asymptomatic plant parts then showed significantly higher quantities in symptomatic parts from samples collected in summer season and no quantity difference in samples collected in winter season.

Hazelnut floral phenology in southern Ontario

Hazelnut (Corylus avellana L.) is a monoecious, dichogamous plant species that flowers in winter and early spring. In traditional hazelnut growing regions, hazelnut cultivars generally express protandry where the male flowers bloom before the female flowers. Nut set requires that compatible pollen be shed when the stigmas of the main cultivar are receptive. In this study, the floral phenology and date of leaf budbreak of five selections and 19 hazelnut cultivars from Europe and North America were observed over 4 yr in southern Ontario, and results were compared with cumulative growing degree days (GDD). In the continental climate of southern Ontario, most cultivars showed protogyny. Flowering dates varied over the years with pollination occurring in a period of 2–3 wk in early spring. These cultivars were classified into early, mid, and late blooming types. A GDD model was a better tool than average daily temperatures to predict the flowering dates of catkins and female flowers. Averaged over years, most of the cultivars in this study have a female bloom that is likely too early for the pollen shed by most of the other cultivars. This would likely impact yields in a commercial orchard. However, ‘Jefferson’, ‘Gene’, and ‘Epsilon’ have late females that are receptive when other cultivars are shedding pollen.

Varying Levels of Genetic Control and Phenotypic Plasticity in Timing of Bud Burst, Flower Opening, Leaf Senescence and Leaf Fall in Two Common Gardens of Prunus padus L.

Several phenological phases mark the seasonal growth pattern in temperate woody perennials. To gain further insight into the way these phases react on an altering growth environment, we tested whether vegetative and reproductive phenophases in a shrub species respond differentially among different genetic entities and between two different planting sites. We scored leaf bud burst, flower opening, leaf senescence and leaf fall on 267 ramets of Prunus padus L. belonging to 53 genotypes that were sampled in 9 local populations, and that were planted in 2 common gardens in the northern part of Belgium. The data were processed with cumulative logistic regression. The contribution of genetic and non-genetic components to the total variability varied between the four studied seasonal phenophases. The timing of flower opening displayed the smallest relative amount of intragenotypic variance (between ramets), suggesting a stronger genetic control and a lesser need at the individual plant level for plastic fine tuning to the micro-environment. In addition, whereas leaf bud burst showed the highest relative variance at the interpopulation level among all phenophases, probably at least partly attributable to local adaptation, flower opening displayed the highest intergenotypic variance, which may have been promoted more by assortative mating. Spring phenophases were strongly correlated (r = 0.89) as well as the autumnal phenophases (r = 0.72). Flower opening was not correlated with the autumnal phenophases. Timing of leaf bud burst and leaf senescence were negatively correlated, demonstrating that the length of the growing season enlarged or diminished among the studied genotypes. Although the two planting sites were only 24 km apart, all phenophases were advanced at the less exposed site, indicating a phenotypic plastic response. Together, our results suggest that in P. padus, flowering is less sensitive to environmental variation than leaf bud break and may show a lesser impact of a changing environment on this reproductive phenophase.

Phenology and yield evaluation of hazelnut cultivars in Latium region

In central Italy (Latium), hazelnut cultivation is carried out using only a few round-shaped nut producing cultivars including ‘Tonda Gentile Romana’, ‘Tonda di Giffoni’ and ‘Nocchione’ as main pollinizer. With the aim to extend the hazelnut genetic base a variety collection was established in a typical hazelnut-growing area of Viterbo province. The collection consists of 48 cultivars, each represented by three multi-stemmed trees. Flowering time, female and male full bloom, leaf budbreak, and leaf fall of each cultivar were recorded over three years (2014-2016). Sucker production and vigor of the trees were also measured. Further, nut yield and nut and kernel traits were investigated. On average, ‘Tonda Rossa’, ‘Karidaty’, ‘Sivri A’ and ‘Tonda Gentile delle Langhe’ showed a very early period of pollen shed, which was concentrated in the middle of December. In respect to female bloom, the earliest female bloom was in ‘Nostrale’, ‘San Giovanni’ and ‘Tonda di Giffoni’, which showed style emergence (red-dot stage) at the end of November. ‘San Giovanni’ and ‘Tonda di Giffoni’ also showed an early leaf budbreak, which occurred in mid-February, and this early vegetative growth could make this cultivar vulnerable to frost injury. ‘Camponica’ showed the highest yield over the period of investigation, and ‘Nociara’ showed the highest yield efficiency.

The first report: Chilling and heat requirements of seedless barberry ( Berberis vulgaris L. var. asperma)

Abstract Seedless barberry (Berberis vulgaris L. var. asperma) is a particular fruit crop that has been used extensively as a medicinal plant in traditional medicine. For the first time, chilling and heat requirements of seedless barberry for breaking of dormancy were calculated. The studied genotypes assayed were selected from Khorasan-e-Jonoobi province in the eastern part of Iran. Uniform one-year-old cuttings were obtained from the shrubs of each genotype after leaf fall and were stored at 4 ± 1 °C for 0.00 (control), 400, 700, 1100 and 1400 h. Six characters including days to the first leaf bud break, days to the first flower bud break, days to full flower bud break, leaf bud number, flower bud number and flowered bunch number were examined. In addition, chilling and heat requirements were determined. Results showed that chilling treatments had significant effects on all the measured traits. The cuttings reached a period of chilling of 1100–1400 h showed the earliest full flower bud break. The highest number of flowered bunches was observed in the cuttings treated with 1400 h chilling. All the genotypes had a chilling requirement of 1400 h. On the contrary, the genotypes were classified into two groups based on heat requirements with 2904 and 3432 growing degree hours (GDHs), however, they were not significantly differed in this regards. In conclusion, the present information can be used to advise seedless barberry farmers about which genotypes are best suited to areas with different winter conditions.

Plant phenological responses to a long-term experimental extension of growing season and soil warming in the tussock tundra of Alaska.

Climate warming is strongly altering the timing of season initiation and season length in the Arctic. Phenological activities are among the most sensitive plant responses to climate change and have important effects at all levels within the ecosystem. We tested the effects of two experimental treatments, extended growing season via snow removal and extended growing season combined with soil warming, on plant phenology in tussock tundra in Alaska from 1995 through 2003. We specifically monitored the responses of eight species, representing four growth forms: (i) graminoids (Carex bigellowii and Eriophorum vaginatum); (ii) evergreen shrubs (Ledum palustre, Cassiope tetragona, and Vaccinium vitis-idaea); (iii) deciduous shrubs (Betula nana and Salix pulchra); and (iv) forbs (Polygonum bistorta). Our study answered three questions: (i) Do experimental treatments affect the timing of leaf bud break, flowering, and leaf senescence? (ii) Are responses to treatments species-specific and growth form-specific? and (iii) Which environmental factors best predict timing of phenophases? Treatment significantly affected the timing of all three phenophases, although the two experimental treatments did not differ from each other. While phenological events began earlier in the experimental plots relative to the controls, duration of phenophases did not increase. The evergreen shrub, Cassiope tetragona, did not respond to either experimental treatment. While the other species did respond to experimental treatments, the total active period for these species did not increase relative to the control. Air temperature was consistently the best predictor of phenology. Our results imply that some evergreen shrubs (i.e., C.tetragona) will not capitalize on earlier favorable growing conditions, putting them at a competitive disadvantage relative to phenotypically plastic deciduous shrubs. Our findings also suggest that an early onset of the growing season as a result of decreased snow cover will not necessarily result in greater tundra productivity.

Climatic Characterization and Phenology of Local Peach Genotypes in the Udzungwa Uplands of Tanzania

The phenology of two local peach genotypes was studied to verify whether peaches can be produced in the Tanzanian uplands. Observations were conducted on trees of one early- and one late-ripening peach genotype in 2010 and 2011. Temperature trends were reconstructed and three chilling estimation models were tested. The two peach genotypes differed for timing of flower and leaf bud-break. Common symptoms of insufficient chilling (presence of numerous stages at a specific date and about 20% of undeveloped flower buds) were observed in the late genotype. Both Utah and Dynamic models indicated low chilling accumulation, lower than the Mean Temperature model in most cases. This is inconsistent with the actual phenology, suggesting that (1) both models show some limitations under our conditions, (2) the two genotypes partly adapted to the local climate, and (3) mechanisms other than chilling (seasonal rainfall fluctuations) play a role in rest control.

Frost hardiness vs. growth performance in trembling aspen: an experimental test of assisted migration

Summary According to the range limit hypothesis, the distribution of many temperate species is restricted by a trade‐off between their capacity to survive winter extremes in the north (or high elevation) and their ability to compete with better‐adapted species in the south (or low elevation range limits). This trade‐off has important implications in forestry, particularly in the context of managed seed movement under climate change. In this study, we aim to quantify trade‐offs among growth, frost hardiness and timing of leaf senescence and bud break in populations of trembling aspen, Populus tremuloides Michx., which were observed in a large reciprocal transplant experiment across five planting sites in western Canada, including additional provenances from Minnesota. After 10 years, we found pronounced increases in productivity as a result of long‐distance transfers in a north‐west direction. For example, provenances moved 1600 km north‐west from Minnesota to central Alberta (a shift of 7° latitude to the north) produced almost twice the biomass of local sources. Similarly, provenances moved 800 km from central Alberta to north‐east British Columbia (4° latitude north) also produced twice the biomass of local sources. We further found that increased growth was not associated with lower survival rates. Bud break in provenances transferred north‐west generally occurred slightly later than in local sources, suggesting decreased risk of spring frost injury. Leaf abscission was later in provenances transferred in a north‐west direction, but they appeared to be very frost hardy, well ahead of very rare early fall frost events. Synthesis and applications. This study demonstrated that assisted migration prescriptions have considerable potential to enhance forest productivity. In the case of aspen, even long‐distance seed transfers in a north‐west direction were successful. We conclude that benefits in productivity outweigh potential risks associated with northward transfer of aspen planting stock under both current and projected future climate conditions.

Response of Highbush Blueberry to Nitrogen Fertilizer during Field Establishment—II. Plant Nutrient Requirements in Relation to Nitrogen Fertilizer Supply

A study was done to determine the macro- and micronutrient requirements of young northern highbush blueberry plants (Vaccinium corymbosum L. ‘Bluecrop’) during the first 2 years of establishment and to examine how these requirements were affected by the amount of nitrogen (N) fertilizer applied. The plants were spaced 1.2 × 3.0 m apart and fertilized with 0, 50, or 100 kg·ha−1 of N, 35 kg·ha−1 of phosphorus (P), and 66 kg·ha−1 of potassium (K) each spring. A light fruit crop was harvested during the second year after planting. Plants were excavated and parts sampled for complete nutrient analysis at six key stages of development, from leaf budbreak after planting to fruit harvest the next year. The concentration of several nutrients in the leaves, including N, P, calcium (Ca), sulfur (S), and manganese (Mn), increased with N fertilizer application, whereas leaf boron (B) concentration decreased. In most cases, the concentration of nutrients was within or above the range considered normal for mature blueberry plants, although leaf N was below normal in plants grown without fertilizer in Year 1, and leaf B was below normal in plants fertilized with 50 or 100 kg·ha−1 N in Year 2. Plants fertilized with 50 kg·ha−1 N were largest, producing 22% to 32% more dry weight (DW) the first season and 78% to 90% more DW the second season than unfertilized plants or plants fertilized with 100 kg·ha−1 N. Most DW accumulated in new shoots, leaves, and roots in both years as well as in fruit the second year. New shoot and leaf DW was much greater each year when plants were fertilized with 50 or 100 kg·ha−1 N, whereas root DW was only greater at fruit harvest and only when 50 kg·ha−1 N was applied. Application of 50 kg·ha−1 N also increased DW of woody stems by fruit harvest, but neither 50 nor 100 kg·ha−1 N had a significant effect on crown, flower, or fruit DW. Depending on treatment, plants lost 16% to 29% of total biomass at leaf abscission, 3% to 16% when pruned in winter, and 13% to 32% at fruit harvest. The content of most nutrients in the plant followed the same patterns of accumulation and loss as plant DW. However, unlike DW, magnesium (Mg), iron (Fe), and zinc (Zn) content in new shoots and leaves was similar among N treatments the first year, and N fertilizer increased N and S content in woody stems much earlier than it increased biomass of the stems. Likewise, N, P, S, and Zn content in the crown were greater at times when N fertilizer was applied, whereas K and Ca content were sometimes lower. Overall, plants fertilized with 50 kg·ha−1 N produced the most growth and, from planting to first fruit harvest, required 34.8 kg·ha−1 N, 2.3 kg·ha−1 P, 12.5 kg·ha−1 K, 8.4 kg·ha−1 Ca, 3.8 kg·ha−1 Mg, 5.9 kg·ha−1 S, 295 g·ha−1 Fe, 40 g·ha−1 B, 23 g·ha−1 copper (Cu), 1273 g·ha−1 Mn, and 65 g·ha−1 Zn. Thus, of the total amount of fertilizer applied over 2 years, only 21% of the N, 3% of the P, and 9% of the K were used by plants during establishment.

Efficacy of Organically Acceptable Materials for Control of Mummy Berry Disease on Lowbush Blueberries in Maine

The efficacy of biological controls and application of mulch for control of the blight stage of mummy berry disease was examined in different lowbush blueberry fields in Maine over 5 years. Biological controls tested included compost teas and commercial products containing Trichoderma harzianum, Bacillus pumilus, B. subtilis, Streptomyces lydicus, and plant extracts of neem, garlic, citrus, and giant knotweed. Treatment with compost teas did not affect numbers of fungal and bacterial colony-forming units on leaves compared to controls. Early application of peat mulch before leaf bud break was partially effective at controlling disease in the field. In 2010, extracts of citrus and giant knotweed and a B. subtilis commercial product were effective at controlling disease in at least one of two fields. The other biological controls did not significantly decrease disease incidence compared to untreated controls.

SEED GERMINATION TIME AS A CRITERION FOR THE EARLY SELECTION OF LATE FLOWERING ALMONDS

With 2 tables Abstract The breeding of new late-flowering almond cultivars is a long process, due mainly to the long juvenile phase of the seedlings. Early selection methods would improve the efficiency of breeding programmes. In this work, we investigated the use of seed germination time to select for late-flowering almonds in 136 seedlings representing six progeny from controlled pollinations performed in 2002. Germination time for seeds with mesocarp and endocarp removed was recorded during stratification, and time of leaf budbreak and flowering were recorded in the fourth and fifth leaf. Within the six progeny evaluated over 2 years, correlations between seed germination and leaf budbreak of the seedlings ranged from 0.02 to 0.43, and for the pooled data averaged 0.48. Correlations between seed germination and seedling flowering time ranged from 0.06 to 0.55, and for the pooled data were 0.50. These results indicate a relationship between times of germination of the seeds and flowering of the resulting seedlings, but the low correlations indicate that the usefulness of selection based in seed germination time will be limited.

Interactive Effects of Light and Chilling on Peach Flower and Leaf Budbreak

Timing of budbreak in response to winter chilling is a critical factor in the suitability of peach [Prunus persica (L.) Batsch] cultivars to moderate climates such as that in the southeastern United States. Much of the research on chilling and dormancy has used excised cuttings or potted trees exposed to various treatments and forced under controlled conditions. Light is not generally considered an important factor in such experiments, and the effect of light during forcing has been little studied. The objective of this research was to compare light versus dark conditions during forcing as well as the effects of different colors of light during forcing. Our results showed that after chilling had been minimally satisfied, peach floral and vegetative budbreak occurred faster when forced in the presence of light than when forced in darkness. Light increased budbreak rate as well as the total percentage of budbreak. Red, yellow, and fluorescent light were more promotive in increasing budbreak than blue, green, infrared, or incandescent light, suggesting a role for phytochrome. Promotive effects of light were less when buds had received enough natural chill and heat to break within a week of forcing at 18 °C. In conclusion, light during forcing can have a significant effect of budbreak and needs to be considered when doing research on chilling and dormancy.

Gamma irradiation influences on some biological traits in two almond (Prunus amygdalus, L) cultivars

Mutation by ionizing radiations such as gamma-rays is being employed as one of the mutation breeding approaches to obtain the desirable mutant cultivars and genotypes in plants. Almond cultivars 'A200' and 'Sahand' are self-incompatible following pollination and fertilization problems. Therefore, obtaining their late-flowering and self-fertile mutants with good biological traits, by means of mutation, will be very bounteous for breeders and producers. This study was conducted to evaluate the effects of different exposition times to gamma-radiation on some biological traits of two late-blooming cultivars ‘A200’ and ‘Sahand’. Current shoots of 'A200' and 'Sahand' were exposed to 36 µC gamma-radiation for 0, 5, 10, 30 and 150 min from the Cobalt 60. The factorial experiment was carried out on 4-year old irradiated trees based on completely-randomized design (CRD) and some biological traits such as: resistance to diseases agents, partial fungus and pests (aphid, mite, etc.), blooming date, leaf bud break date, bearing type, leaf area (LA) and flower density were investigated in all irradiated plants. Results showed that long exposition times have significant positive effects on resistance to disease agents such as: polystigma occharaceum, mite, LA and flower density, but did not have significant effect on bearing type, resistance to aphids, blooming and leaf bud break dates in spring. Effects of cultivars were significant on resistance to pests (aphid, mite and other main destructive pests) and diseases agents and bearing type, while no significance was seen on blooming, leaf bud break dates, LA and flower density. Interaction effect between cultivars and exposition time was significant on resistance to diseases, mite and flowering date, but was not significant on LA, flower density, resistance to aphid and leaf bud break date. However, the maximum resistance to diseases agents, aphid and mite was observed in plants irradiated 150 min in both cultivars. Key words: Almond, breeding, mutants, gamma-irradiation, biological traits.

Dynamics of Ascospore Maturation and Discharge in Erysiphe necator, the Causal Agent of Grape Powdery Mildew

Dynamics of ascocarp development, ascospore maturation, and dispersal in Erysiphe necator were studied over a 4-year period, from the time of ascocarp formation to the end of the ascosporic season at the end of June in the following spring. Naturally dispersed chasmothecia were collected from mid-August to late November (when leaf fall was complete); the different collections were used to form three to five cohorts of chasmothecia per year, with each cohort containing ascocarps formed in different periods. Chasmothecia were exposed to natural conditions in a vineyard and periodically sampled. Ascocarps were categorized as containing mature or immature ascospores, or as empty; mature ascospores inside chasmothecia were enumerated starting from late February. Ascospore discharge was determined using silicone-coated slides that were placed 3 to 4 cm from sections of the vine trunk holding the chasmothecia. Before complete leaf fall, 34% of the chasmothecia had mature ascospores, 48% had immature ascospores, and 18% were empty; in the same period, the trapped ascospores represented 56% of the total ascospores trapped in an ascosporic season (i.e., from late summer until the next spring or early summer). The number of viable chasmothecia diminished over time; 11 and 5% of chasmothecia had mature ascospores between complete leaf fall and bud break and after bud break, respectively. These ascocarps discharged ≈2 and 42% of the total ascospores, respectively. All the ascocarp cohorts released ascospores in autumn, survived the winter, and discharged viable ascospores in spring; neither ascospore numbers nor their pattern of temporal release was influenced by the time when chasmothecia were collected and exposed in the vineyard. Abundance of mature ascospores in chasmothecia was expressed as a function of degree-days (DD) (base 10°C) accumulated before and after bud break through a Gompertz equation (R² = 0.92). Based on this equation, 90% of the ascospores were mature when 153 DD (confidence interval, 100 to 210 DD) had accumulated after bud break. Most ascospores were trapped in periods with >2 mm of rain; however, a few ascospores were airborne with <2 mm of rain and, occasionally, in wet periods of ≥3.5 h not initiated by rain.

Seed germination time as a criterion for the early selection of late-flowering almonds

With 2 tables Abstract The breeding of new late-flowering almond cultivars is a long process, due mainly to the long juvenile phase of the seedlings. Early selection methods would improve the efficiency of breeding programmes. In this work, we investigated the use of seed germination time to select for late-flowering almonds in 136 seedlings representing six progeny from controlled pollinations performed in 2002. Germination time for seeds with mesocarp and endocarp removed was recorded during stratification, and time of leaf budbreak and flowering were recorded in the fourth and fifth leaf. Within the six progeny evaluated over 2 years, correlations between seed germination and leaf budbreak of the seedlings ranged from 0.02 to 0.43, and for the pooled data averaged 0.48. Correlations between seed germination and seedling flowering time ranged from 0.06 to 0.55, and for the pooled data were 0.50. These results indicate a relationship between times of germination of the seeds and flowering of the resulting seedlings, but the low correlations indicate that the usefulness of selection based in seed germination time will be limited.

Sucrose phosphate synthase expression influences poplar phenology

The objective of this study was to manipulate the intracellular pools of sucrose, and investigate its role in regulating plant growth, phenology (leaf senescence and bud break) and fibre development. This objective was achieved by differentially expressing an Arabidopsis (Arabidopsis thaliana L. Heynh.) sucrose phosphate synthase (SPS) gene in hybrid poplar (Populus alba L.xPopulus grandidentata Michx.), a model system for tree biology with substantial industrial relevance in the context of short rotation forestry and a target bioenergy crop. Phenotypic differences were evident in the transgenic trees, as both the timing of bud flush and leaf senescence were altered compared to wild-type (WT) trees. Tree height and stem diameter were similar in WT and in the AtSPS transgenic trees, however, there were differences in the length of xylem fibres. Elevated concentrations of intracellular sucrose in both leaf and stem tissue of the transgenic trees are associated with a prolonged onset of senescence and an advancement in bud flush in the following spring. The association among sucrose content, tree phenology and elevated SPS gene expression implicates both enzyme and product in regulating poplar developmental processes.