The effect of summer shading on flower bud morphogenesis in apricot (Prunus armeniaca L.)

Morphological and physiological investigations reveal the regulatory effect of exogenous paclobutrazol on flowering promotion by winter warming in Chaenomeles speciosa 'Changshouguan'

The application of exogenous paclobutrazol (PP333) can improve the ability of winter warming to promote flowering in Chaenomeles speciosa, but the underlying mechanism is unclear. In this study, the cultivar 'Changshouguan' was sprayed with different concentrations of PP333 during flower bud differentiation, and the changes in the anatomical structures and physiological characteristics of the flower buds during the differentiation process, as well as the growth state of the flower buds and the effect on flowering promotion after winter warming treatment, were comprehensively investigated. The results showed that different concentrations of PP333 could advance the flowering time of 'Changshouguan' by 15-24 d under the warming treatment and increase the flowering duration to 17 d compared with those under the warming treatment alone (CK), and 1000 mg/L was the best treatment. Compared with the CK treatment, the PP333 treatment decreased the contents of indole acetic acid (IAA) and gibberellic acid (GAs) and increased the contents of zeatin ribosides (ZRs) and abscisic acid (ABA), thus changing the balance of hormones during flower bud differentiation. The inflection point (low point) of the curve shapes of the ZRs/GAs and ZRs/IAA ratios appeared significantly earlier, which showed a pattern consistent with soluble sugar and protein content and antioxidant activity. Interestingly, the above changes also corresponded to earlier flowering times during the warming process. Taken together, these results indicate that spraying an appropriate concentration of PP333 in the early stage of 'Changshouguan' flower bud differentiation promotes the early differentiation of flower buds and early flowering under winter warming treatment by altering their endogenous hormone content and homeostasis and changing their physiological state. The key to maintaining a relatively long flowering period in plants in the PP333 treatment group after flowering promotion was the increased accumulation of sugars and proteins.

Inflorescence Traits and Floral Quality Parameters in Promising Olive Clones (cv Leccino): Influence of the Canopy Position

In olive (Olea europaea L.), the floral quality is a key feature affecting the final fruit crop. The aim of this study was to evaluate the inflorescence traits and the floral quality parameters of three clones of Leccino cultivar (L 1.3, L 1.4, L 1.9). To assess a possible effect of light limitations on these parameters two canopy zones, internal (IZ) and external (EZ), were considered. The inflorescences were collected over two consecutive years in order to establish: (i) the characteristics of inflorescences (length, flowers per inflorescence) and flowers (open and perfect flowers); (ii) the ovary structure by histological analysis; and (iii) the viability and germination of pollen grains by in vitro culture. The preliminary results highlighted some differences among clones. The L 1.9 was the less affected by the canopy position for inflorescence morphological traits, and the presence of ovaries with at least three fully developed ovules denoting a high female fertility. Regardless of the canopy position, L 1.4 showed the highest pollen viability, suggesting its possible use as pollinator. The lower sensitivity of female and male floral organs to partial shading of L 1.9 and L 1.4 needs further investigations aimed at evaluating their suitability in high-density olive orchards.

Summer pruning of sweet cherry: a way to control sugar content in different organs

BACKGROUND

Sweet cherry trees (Prunus avium L.) of the cultivar Grace Star were pruned either in dormancy or in summer. The response was studied by analyzing the sugar content in different organs (flower bud, leaf, and fruit) at three sections of the canopy (inner, outer, and upper) using high-performance liquid chromatography. The effect of summer pruning was evaluated by measuring photosynthetic photon flux density (PPFD) and leaf chlorophyll content (SPAD).

RESULTS

In this study, the timing of pruning had a significant effect on sugar content in flower buds, leaves, and fruit. Trees pruned in summer had higher glucose, fructose, sorbitol, and sucrose content in flower buds, higher glucose and fructose contents in leaves, and lower fructose, sorbitol, and total sugar content in fruit than in trees pruned at dormancy. Higher average PPFD and lower SPAD values were measured in the inner canopy of trees pruned in summer. All measured parameters were influenced by position in the canopy. The lowest fructose and sorbitol contents in the flower bud, the lowest content of glucose, fructose, sorbitol, total sugars and the highest SPAD values in the leaf, while less dark and lighter fruit were measured in the inner part of the canopy.

CONCLUSION

Summer pruning affects sugar distribution in the tree by altering irradiation conditions within the canopy. Our results suggest that summer pruning is an effective technological measure to improve sugar content in the buds. A strong, well nourished flower bud is a good indication of high fruit production next season. © 2021 Society of Chemical Industry.

The Effects of Canopy Height and Bud Light Exposure on the Early Stages of Flower Development in Prunus persica (L.) Batsch

The aims of this study were to investigate the sunlight requirements during floral initiation and differentiation for the development of flower buds in 'Autumn Bright' nectarine and to explore its source-sink relationship. In early January 2019 (111 days after full bloom), prior to floral initiation and differentiation, 12 new shoots were tagged on 14 trees, with four shoots in each of the low (0-1.2 m), middle (1.2-2.0 m), and high (>2.0 m) canopy heights. Three treatments (bud shading; leaf pluck; bud shading and leaf pluck) were applied to three shoots in each canopy height on the fourth and eighth bud, in addition to a fourth control shoot. Light penetration was measured at the different canopy heights. Buds were assessed in Spring for floral transition, number of floral buds per node, and fruit set. The treatments at the node level had no effect on floral initiation, indicating that sink strength was not promoted by additional light. Light penetration decreased with decreasing canopy height and corresponded with lower floral buds in the low zone. Fruit set was uninfluenced by all treatments. The results of this study emphasised the importance of the availability of photosynthetic assimilates for floral initiation in peach and nectarine trees. Balanced crop load management and summer pruning to enhance canopy sunlight distribution would increase the availability of nutrients for improved floral transition in this cultivar.