Browsing by Subject "Flower induction"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Publication
    Changes in the concentration of particular hormones and carbohydrates in apple shoots after "bending" respectively chemical treatments and relationship to the flower induction process
    (2005) Boonplod, Nopporn; Bangerth, Fritz
    SUMMARY Apples are cultivated commercially throughout the temperate zone. A regular production however does not seem possible because of irregular yields from year to year. Main causes for this are the so called "alternate bearing" behavior which is the result of profuse flowering in one year but few or no flowers in the following year. It is reported that too vigorously growing shoots are part of the reasons for alternate bearing in apple trees. Applications of chemicals or conventional cultural practices, such as bending shoots have been widely used to restrict shoot growth and promote flower induction. However, the physiological mode of action of these methods in FI is still unknown. Phytohormones are thought to be involved in the process of flower induction (FI). In the above experiments, we investigated changes in endogenous hormones, starch and sugar contents after bending upright shoots into a horizontal position and spraying apple trees with the growth regulators Alar plus Ethrel to improve FI. The experiments were carried out during the years 2001 to 2003 at the Experiment Station, of the University of Hohenheim, Germany, whereby the apple cvs. ?Golden Delicious?, ?Boskoop?, ?Elstar? and ?Idared? were used. The apical part of growing shoots and non-growing bourse shoots, beside bark, wood and shoot diffusates were collected. Plant samples were frozen immediately in liquid nitrogen and freeze dried. Phosphate buffer 0.1M, pH 6.2 was used for collecting auxin in the shoot diffusates. All samples were stored at ?20C until extraction and purified, identified and quantified by Radio Immuno Assay (RIA). The results revealed, in general, that shoot bending and spraying with Alar plus Ethrel changed the endogenous hormone concentrations in the apical part of shoots, as well as in wood, bark and shoot exudates of apple trees. The ?Golden Delicious? cultivar and vigorously growing shoots showed clearer tendencies of hormonal changes than the other cvs. and non-growing bourse shoots. Cytokinin concentrations in the apical part of shoots, and in wood and bark increased after both treatments. Contrary to that, GAs and IAA concentrations in the apical part of shoots and in shoot exudates showed the opposite results. Both treatments had no effect on the concentration of ABA. Ethylene production in shoot tips was considerably stimulated by the combined treatment of Ethrel plus Alar probably due to Ethrel being a "synthetic precursor" of ethylene. Considerable variation existed in the mentioned hormonal changes in respect to the year of examination and the cv. under investigation. Time of treatments and in particular climatic conditions were probably the most influential variables. In spite of all this and on the basis of the above results the conclusion can be drawn that higher concentrations of cytokinins and lower concentrations of gibberellins and auxin are favorable for FI. Spraying with Alar plus Ethrel and bending of shoots seemed to decrease the reducing-sugars, as well as sucrose and starch concentrations in growing shoots and their leaves. In non-growing shoots, spraying seemed to reduce starch but to increase reducing-sugars and sucrose concentrations. A correlation between changes in carbohydrate contents (reducing sugar, sucrose and starch) caused by the spraying treatments and FI does not seem to exist. All the observed changes in the carbohydrate concentrations caused by spraying treatments were not particular impressive and did not really support the often published claim that the effect of spraying growth regulators, bending shoots or other cultural practices may mediate their stimulatory effect on FI via a change in carbohydrates. In contrast to that the above observed experimental results rather suggest that hormones are more effectively involved in the flower induction process of fruit trees.
  • Thumbnail Image
    Publication
    Physiological, metabolic and molecular basis of biennial bearing in apple
    (2023) Kofler, Julian; Zörb, Christian
    Alternate or biennial bearing in apple (Malus ×domestica Borkh.) is characterized by ‘On’ years with high crop load and inhibited floral bud initiation and ‘Off’ years with little crop load and promoted formation of floral buds, respectively. Apple cultivars differ in their degree of biennial bearing behavior. The cropping irregularity has severe effects on quality and yield of apple harvests in commercial orchards and thereby directly poses an economic risk to apple growers. The aim of this study was to contribute to the understanding of the underlying mechanisms of biennial bearing in apple by analyzing the physiological processes in bud meristems during the time of flower bud induction. A field experiment was conducted during the growing seasons 2015 and 2016 and provided bud meristems of various developmental stages for a variety of analyses. The regular bearing cultivar ‘Royal Gala’ and the biennial bearing cultivar ‘Fuji’ allowed the comparison of two different developmental responses to high and low crop load treatments. Buds from 2-year-old spurs were sampled starting approximately four weeks after full bloom. Histological analysis of bud meristems successfully identified the time point of flower bud initiation in both cultivars at the experimental site. The onset of flower bud initiation was affected by crop load, cultivar and heat accumulation. While heavy cropping delayed the onset in ‘Royal Gala’ trees for 20 days compared to ‘Royal Gala’ trees with no crop load, bud initiation in heavy cropping ‘Fuji’ trees was negligible. ‘Fuji’ trees with no crop load started initiating buds 19 days earlier than ‘Royal Gala’ trees with the same cropping status. Proteomic profiling of the buds sampled during flower bud induction and during flower bud initiation revealed distinct differences in specific protein abundances depending on the cropping status. Buds from trees with a high crop load, where the flower bud initiation was inhibited and the buds primarily remained in a vegetative state, showed a decreased abundance of enzymes belonging to the phenylpropanoid and flavonoid pathways. Specifically, PAL was reduced, which could lead to less active auxin due to the reduced production of chlorogenic acid and thereby inhibiting flower bud formation. Furthermore, increased abundances of histone deacetylase and ferritins were also found in buds from high cropping trees, indicating that histone modification and building up enough iron storage capacities are involved in the vegetative bud development. Buds growing on non-cropping trees with a high rate of flower bud initiation, showed significantly higher concentrations of proteins involved in histone and DNA methylation. Metabolomic profiling and next-generation RNA sequencing showed that thiamine, chlorogenic acid, and an adenine derivative play a role in metabolic pathways promoting early flower bud development in apple, and that tryptophan was more abundant in buds collected from high-cropping trees compared to non-cropping trees. The selection of proteins, metabolites, and genes that the current work produced through its broad, non-targeted approach provides a comprehensive data base for future, more targeted analyses. The results of this study lay a thorough baseline to contribute to the identification of biological markers that are linked to a certain bearing behavior. Such markers can accelerate and facilitate breeding programs aimed at selecting apple cultivars, that are less prone to biennial bearing.