Effects of Exogenous Gibberellic Acid in Huanglongbing-affected Sweet Orange Trees under Florida Conditions – I. Flower Bud Emergence and Flower Formation

Under Florida conditions, sweet orange (Citrus sinensis) affected by Huanglongbing {HLB [Candidatus Liberibacter asiaticus (CLas)]} frequently exhibits irregular flowering patterns, including off-season flowering and prolonged bloom period. Such patterns can increase the opportunity for temporal and spatial proliferation of pathogens that infect flower petals, including the fungal causal agent for postbloom fruit drop (PFD) Colletotrichum acutatum J.H. Simmonds. For the development of strategies to manipulate flowering, the effects of floral inhibitor gibberellic acid (GA3) sprayed monthly at full- and half-strength rates (49 and 25 g·ha−1, or 33 and 17 mg·L−1, respectively) with different regimens, starting from September and ending in November, December, or January, on the pattern of spring bloom were evaluated in field-grown HLB-affected ‘Valencia’ sweet orange at two locations in subsequent February through April for two separate years in this study. To further examine whether GA3 effects on flowering patterns vary in different cultivars, early-maturing ‘Navel’ sweet orange trees receiving no GA3 or full-strength GA3 monthly in September through January were included. Overall, for ‘Valencia’ sweet orange, monthly applications of GA3 at 49 g·ha−1 from September to December not only minimized the incidence of scattered emergence of flower buds and open flowers before the major bloom but also shortened the duration of flowering, compared with the untreated control trees. In addition, exogenous GA3 led to decreased leaf flowering locus t (FT) expression starting in December, as well as reduced expression of its downstream flower genes in buds during later months. When applied monthly from September through January at 49 g·ha−1, similar influences of exogenous GA3 on repressing flower bud formation and compressing bloom period were observed in ‘Navel’ sweet orange. These results suggest that by effectively manipulating flowering in HLB-affected sweet orange trees under the Florida climate conditions, exogenous GA3 may be used to reduce early sporadic flowering and thereby shorten the window of C. acutatum infection that causes loss in fruit production.

The Effect of Supplementary LED Lighting on the Morphological and Physiological Traits of Miniature Rosa × Hybrida ‘Aga’ and the Development of Powdery Mildew (Podosphaera pannosa) under Greenhouse Conditions

We investigated the growth traits, flower bud formation, photosynthetic performance, and powdery mildew development in miniature Rosa × hybrida ‘Aga’ plants grown in the greenhouse under different light-emitting diode (LED) light spectra. Fluorescence-based sensors that detect the maximum photochemical efficiency of photosystem II (PS II) as well as chlorophyll and flavonol indices were used in this study. Five different LED light treatments as a supplement to natural sunlight with red (R), blue (B), white (W), RBW+FR (far-red) (high R:FR), and RBW+FR (low R:FR) were used. Control plants were illuminated only by natural sunlight. Plants were grown under different spectra of LED lighting and the same photosynthetic photon flux density (PPFD) (200 µmol m−2 s−1) at a photoperiod of 18 h. Plants grown under both RBW+FR lights were the highest, and had the greatest total shoot length, irrespective of R:FR. These plants also showed the highest maximum quantum yield of PS II (average 0.805) among the light treatments. Red monochromatic light and RBW+FR at high R:FR stimulated flower bud formation. Moreover, plants grown under red LEDs were more resistant to Podosphaera pannosa than those grown under other light treatments. The increased flavonol index in plants exposed to monochromatic blue light, compared to the W and control plants, did not inhibit powdery mildew development.

Gibberellin and spermidine synergistically regulate polyamine metabolism during Rhododendron flower development

Polyamines (PAs) are involved in various plants developmental processes, especially in flowering. Their significant influence has been established, but the exact mechanisms by which PAs modulate flowering are not yet understood. To understand the PA metabolism during flowering/senescence in Rhododendron simsii ‘Zichendian’ plants, exogenous gibberellin (GA3, 0-2400 mg L− 1) and spermidine (Spd, 0–1 mM) were applied separately or in combination during the early stage of flower bud formation. The application of GA3 alone advanced the initial flowering by promoting the free Put (F) fraction and decreasing the Spd/Put ratio at the squaring stage, whereas Spd alone delayed the initial flowering by increasing the soluble conjugated (C) form, insoluble bound Put (B) fraction and Spd/Put ratio. When GA3 plus Spd was applied, the initial flowering advanced by 2 days. Furthermore, endogenous PA levels as well as the C and B fractions of PAs and key enzymes (diamine oxidase, PA oxidase, arginine decarboxylase, ornithine decarboxylase and S-adenosylmethionine decarboxylase) of PA metabolism increased, while the Spd/Spm ratio decreased by GA3 and Spd applications during flowering, resulting in delayed flower senescence. In addition, the structural equation model (SEM) showed that Spd directly participated in PA metabolism, while GA3 regulated flowering by modulating PA metabolism via Spd (c.f. 0.27). Taken together, our study provides comprehensive evidence regarding the clear relationships between GA3, Spd and flowering time, supporting the positive effect of PA metabolism on delaying flower senescence, and helps to provide a thorough understanding of the PA interconversions, biosynthesis and catabolism during flowering and senescence.

Effects of carbon, nitrogen, phosphorus, and potassium on flowering and Fruiting of Glycyrrhiza uralensis

Carbon (C), nitrogen (N), phosphorus (P), and potassium (K) play an important role in flower bud differentiation and seed-filling; however, the effects of these elements on the flowering and fruiting of Glycyrrhiza uralensis Fisch. are not known. In this study, we evaluated the differences in the C, N, P, and K levels between the fruiting and nonfruiting plants of G. uralensis at different growth stages. The correlations between the elements C, N, P, and K and the flower and fruit falling rates, rate of empty seeds, rate of shrunken grains, and thousand kernel weight (TKW) were also determined. The results show that the P and K levels and C:N, P:N, and K:N ratios of flowering plants are significantly higher than those of nonflowering plants; N level of flowering plants is significantly lower than that of nonflowering plants at the flower bud differentiation stage. The number of inflorescences was positively correlated with C and K levels and C:N and K:N ratios. A low level of C, P, and K and high level of N in flowering and pod setting stage may lead to the flower and fruit drop of G. uralensis. The K level is significantly negatively correlated with the rates of empty and shrunken seeds. The N level is significantly positively correlated with TKW. Thus, high levels of C, P, and K might be beneficial to flower bud differentiation, while higher levels of N is not beneficial to the flower bud formation of G. uralensis. Higher levels of N and K at the filling stage were beneficial to the seed setting and seed-filling of G. uralensis.HighlightHigh levels of C, P, and K might be beneficial to flower bud differentiation, while higher levels of N is not beneficial to the flower bud formation of G. uralensis. Higher levels of N and K at the filling stage were beneficial to the seed setting and seed-filling of G. uralensis.

How Supplementary or Night-Interrupting Low-Intensity Blue Light Affects the Flower Induction in Chrysanthemum, A Qualitative Short-Day Plant

This research examined the effects of the supplementary or night-interrupting (NI) blue (B) light supplied at a low intensity on the flowering, gene expression, and morphogenesis of chrysanthemum, a qualitative short-day plant. White (W) light-emitting diodes (LEDs) were used to provide light with a photosynthetic photon flux density (PPFD) of 180 μmol·m−2·s−1 during the photoperiod to grow the plants in a plant factory. The control group was constructed with plants that were exposed to a 10-h short day (SD10) treatment without any blue light. The B light in this research was used for 4 h to either (1) extend the photoperiod for plants at the end of a 9-h short day (SD) treatment as the sole light source (SD9 + 4B), (2) provide night interruption (NI) to plants in the 13-h long-day (LD) treatment (LD13 + NI − 4B), (3) provide NI to plants in the 10-h SD treatment (SD10 + NI − 4B), or (4) supplement the W LEDs at the end of a 13-h LD treatment (LD13 + 4B). Blue LEDs were used to provide the supplementary/NI light at 10 μmol·m−2·s−1 PPFD. The LD13 + NI − 4B treatment resulted in the greatest plant height, followed by LD13 + 4B. Plants in all treatments flowered. It is noteworthy that despite the fact that chrysanthemum is a qualitative SD plant, chrysanthemum plants flowered when grown in the LD13 + 4B and LD13 + NI − 4B treatments. Plants grown in the LD13 + 4B had the greatest number of flowers. Plants grown in the LD13 + 4B treatment had the highest expression levels of the cryptochrome 1, phytochrome A, and phytochrome B genes. The results of this study indicate that a 4-h supplementation of B light during the photoperiod increases flower bud formation and promotes flowering, and presents a possibility as an alternative method to using blackout curtains in LD seasons to practically induce flowering. The B light application methods to induce flowering in SD plants requires further research.

Columnar growth phenotype in apple results from gibberellin deficiency by ectopic expression of a dioxygenase gene

The apple cultivar McIntosh Wijcik, which is a mutant of ‘McIntosh’, exhibits a columnar growth phenotype (short internodes, few lateral branches, many spurs, etc.) that is controlled by a dominant Co gene. The candidate gene (MdDOX-Co), encoding a 2-oxoglutarate-dependent dioxygenase, is located adjacent to an insertion mutation. Non-columnar apples express MdDOX-Co in the roots, whereas columnar apples express MdDOX-Co in the aerial parts as well as in the roots. However, the function of MdDOX-Co remains unknown. Here, we characterized tobacco plants overexpressing MdDOX-Co. The tobacco plants showed the typical dwarf phenotype, which was restored by application of gibberellin A3 (GA3). Moreover, the dwarf tobacco plants had low concentrations of endogenous bioactive gibberellin A1 (GA1) and gibberellin A4 (GA4). Similarly, ‘McIntosh Wijcik’ contained low endogenous GA4 concentration and its dwarf traits (short main shoot and internodes) were partially reversed by GA3 application. These results indicate that MdDOX-Co is associated with bioactive GA deficiency. Interestingly, GA3 application to apple trees also resulted in an increased number of lateral branches and a decrease in flower bud number, indicating that gibberellin (GA) plays important roles in regulating apple tree architecture by affecting both lateral branch formation (vegetative growth) and flower bud formation (reproductive growth). We propose that a deficiency of bioactive GA by ectopic expression of MdDOX-Co in the aerial parts of columnar apples not only induces dwarf phenotypes but also inhibits lateral branch development and promotes flower bud formation, and assembly of these multiple phenotypes constructs the columnar tree form.

Development of Peach Flower Buds under Low Winter Chilling Conditions

Here, we reviewed both endogenous and exogenous factors involved in the processes of flower bud formation and flower development in peach, analyzing how they can be affected by climatic change in temperate zones, explored the expansion of peach to tropical or subtropical zones. The process of flower bud formation in peach differs between low winter chilling and temperate conditions. Although the main steps of flower development are maintained, the timing in which each one occurs is different, and some processes can be altered under low winter chilling conditions, with a great impact on fruit production and crop management. Further studies on flower bud induction and differentiation under warmer conditions are fundamental for addressing the alterations in flower bud development that negatively impact on next season’s harvest. In the future, horticulturalists and scientists will face several challenges, mainly how high temperatures affect the expression of the main genes regulating flower formation and how to improve crop management in these conditions.

Analyses of morphobiochemical characteristics of the Iris genus within the conditions of the Kuzbass botanic garden

The results of study of adaptation potential of plants of the Iris genus of Iridaceae within the conditions of the Kuzbass botanic garden are represented in the article. It was made the evaluation of Morphobiologic characteristics of irises, the terms of flowering was determined together with duration and productivity of flowering, different capacity to fructification was marked, and the sums of positive temperatures need to such phonological phases of development, as growth, flower-bud formation, flowering and fructification were determined. The overall estimate over the complex of decorative signs showed that they are original and stable in the local conditions and may be recommended for commercial floriculture and greening within the conditions of Kemerovo region.Studied an indicating role of phenol compounds, peroxidases, ascorbic acid in Iris leaves during seasonal development. Analyses of studies revealed that the level of biochemical values in the leaves of decorative perennials growing on the territory of the Kuzbass botanic garden depended from species peculiarities and vegetation period of plants. Within the period of vegetation the most accumulation of ascorbic acid was revealed. The studied figures may be used as an informative parameter for the plants state evaluation for further phytoindication and introduction.

Resistance of plants colonized by associative microorganisms to xenobiotics and phytopathogens

The aim of our work was to study the colonization of potato, tomato, rapeseed and camelina by associative microorganisms Methylobacterium mesophilicum, Pseudomonas aureofaciens BS1393 and Pseudomonas putida BS3701; examine the resistance of colonized plants to biotic (phytopathogens Erwinia carotovora and Sclerotinia sclerotiorum) and abiotic (naphthalene, oil) stressors. Colonized plants were characterized by an increased growth rate (1.5–2.0 times higher) compared to non-colonized ones; flower-bud formation, flowering and fructification of the colonized plants also started earlier. An increased resistance of colonized plants to phytopathogens, naphthalene (100 mµ/ml) and oil (0.7 %) was noted, too. The level of superoxide dismutase (SOD) in control plants on a medium with naphthalene or oil increased by 160–150%; in colonized plants – by 20–18 %. Colonized plants were more viable because of the presence of P. putida BS3701 on the roots.