Citrus Flowers Research Articles

Attractiveness of Tetragonula laeviceps (Hymenoptera: Apidae) to Citrus Volatile Compounds and Flower Colors in Indoor Microclimate Conditions

Tetragonula laeviceps plays a vital role as a primary pollinator of citrus flowers for successful pollination. However, there is still a lack of understanding about how T. laeviceps can find citrus flowers. This study aimed to elucidate the factors influencing the attraction of T. laeviceps to citrus flowers, focusing on microclimate conditions, and visual and olfactory factors. For this, we conducted six-choice assays in a stingless bee house using artificial flowers as visual cues and citrus essential oils as olfactory stimuli. Three pairs of red or white artificial flowers were displayed to adult workers, with each pair placed in glass vials filled with diluted orange (Citrus reticulata) essential oil, lemon (Citrus limon) essential oil, or solvent. Simultaneously, microclimate conditions were measured, including temperature, relative humidity, and light intensity. We observed that the highest number of T. laeviceps visited the artificial flowers at 11:00, irrespective of visual and olfactory factors. We also found a positive correlation between the number of visits and both temperature and light intensity, whereas there was a negative correlation with humidity. The number of visits did not exhibit a significant difference between flower colors. In contrast, we observed the highest visitation to the orange essential oil, followed by the lemon essential oil and solvent. Gas Chromatograph – Mass Spectrometry (GC-MS) analysis revealed common terpenes in orange and lemon essential oils, while linalool and α-citral were predominantly detected in the orange essential oil. These characteristic terpenes could potentially be the attractants for T. laeviceps.

Comparative investigation on the aroma profiles of edible citrus flowers in the main organs and different developmental stages

Pomelo flowers emit a strong fragrance and give aromatic odors. Volatile compounds from pomelo flowers were analyzed at three developmental stages and in the main organs by molecular sensory science. A total of 134 volatiles including 25 odorants, were analyzed by gas chromatography–mass spectrometry/pulsed flame photometric detector (GC–MS/PFPD) and multidimensional GC–MS/olfactory (MDGC–MS/O). The total volatile content varied among pomelo flowers at different developmental stages (stage-III > stage-II > stage-I) and among different organs of pomelo flowers (petal > pistil > stamen). Linalool was an important odorant with a high OAV, and floral/fruity comprised the predominant aroma profile. Four odorants, ethyl 2-methylbutanoate, linalool, β-myrcene, and 2-butenal, were selected based on variable importance in projection (VIP) values and contributed mainly to the discrimination of pomelo flowers at three different developmental stages. Linalool, β-myrcene, d-limonene, and ethyl hexanoate were potential markers for evaluating flavor differences in pomelo floral organs.

Synergistic effect of seaweed extract and boric acid and/or calcium chloride on productivity and physico-chemical properties of Valencia orange.

Many citrus species and cultivars are grown successfully in tropical and subtropical countries, as well as in arid and semi-arid regions with low levels of organic matter and low cation exchange, resulting in lower nutrient uptake by the plant. The essential nutrients needed for citrus flowering and fruit set are limited in winter due to a reduction in transpiration rate, negatively effecting vegetative growth, flowering, yield, and fruit quality. The present investigation was carried out to assess the nutritional status, fruit yield parameters, and fruit quality of Valencia orange trees after foliar spraying of seaweed extract (SW) combined with calcium chloride and boric acid and their combinations in the 2020/2021 and 2021/2022 seasons. The treatments were arranged in a split-plot design (three levels spraying seaweed extract × four levels spraying calcium chloride and boric acid and their combinations × four replicates × one tree/replicate). The results indicated that all of the characteristics measured, including leaf chlorophyll, leaf mineral contents, fruit yield parameters, fruit physical properties, and fruit chemical properties, were significantly affected by the foliar spraying of seaweed extract (SW) combined with calcium chloride and boric acid and their combinations. Although all treatments increased the productivity and the physical and chemical properties of Valencia orange fruits compared to the control, a treatment of 10 g/L SW combined with 0.5 g/L boric acid and 1 g/L calcium chloride produced superior results. This ratio of SW, boric acid, and calcium chloride is therefore recommended to enhance productivity and improve the physico-chemical properties of Valencia orange for greater fruit yield.

Determination of volatile components of citrus flowers and leaves growing in Hatay, Türkiye

Species belonging to the genus Citrus are produced and traded in large amounts around the world. In addition to the consumption of citrus fruits as food due to their high vitamin C content, their use in many areas has become widespread with the development of the plant-based products industry. In this study, the amount and structure of volatile components of leaves and flowers of 5 different citrus species (Citrus aurantium, Citrus limon, Citrus paradisi, Citrus reticulata, and Citrus sinensis) were determined using the solid phase micro extraction. Monoterpene hydrocarbons and their oxygenated derivatives were identified as the most abundant chemical component groups. Limonene was the dominant compound in Citrus limon flowers (36.5%), leaves (22.5%) and Citrus paradisi flowers (22.4%). Linalool, and sabinene were the other major components. Linalool was determined at 50.5% in flowers and 73.3% in leaves of Citrus aurantium. Moreover, sabinene had a high amount in Citrus sinensis flowers (19.7%), leaves (24.7%), and in Citrus paradisi (27.4%) leaves. Apart from these dominant components, γ-terpinene (13.9%) and p-cymene (25.4%) were detected in Citrus reticulata flowers and leaves in an important amount. It was seen that the leaves and flowers of Citrus species gathered from Hatay province were an important source of limonene and linalool compounds.

Non-targeted metabolomic analysis reveals the mechanism of quality formation of citrus flower-green tea.

Citrus flower-green tea (CT) is a scented tea processed from green tea (GT) and fresh citrus flower, which is favored by consumers due to its potential health benefits and unique citrus flavor. This study evaluated the quality of CT and revealed the mechanism of its quality formation. The CT had a significant citrus flavor and a good antioxidant activity, and its sensory quality was superior to that of GT. Headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis revealed that the scenting process resulted in a significant increase of alkenes such as β-pinene, trans-β-ocimene, α-farnesene, isoterpinolene, and γ-terpinene, as well as a significant decrease of alcohols such as α-terpineol, l-menthol, and linalool in CT in comparison with GT. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that the levels of flavonoids (such as neohesperidin, hesperidin, tangeritin, hesperetin 5-O-glucoside, and nobiletin) and alkaloids (such as trigonelline and theobromine) in CT increased significantly after scenting process, while the levels of amino acids (such as valine and l-phenylalanine) and organic acids (such as ascorbic acid) decreased significantly. These observations showed that the scenting process promoted the absorption of aroma from citrus flowers by GT and the changes in its non-volatile metabolites, leading to the formation of citrus flavor quality in CT. © 2024 Society of Chemical Industry.

ACC SYNTHASE4 inhibits gibberellin biosynthesis and FLOWERING LOCUS T expression during citrus flowering.

Flowering is an essential process in fruit trees. Flower number and timing have a substantial impact on the yield and maturity of fruit. Ethylene and gibberellin (GA) play vital roles in flowering, but the mechanism of coordinated regulation of flowering in woody plants by GA and ethylene is still unclear. In this study, a lemon (Citrus limon L. Burm) 1-aminocyclopropane-1-carboxylic acid synthase gene (CiACS4) was overexpressed in Nicotiana tabacum and resulted in late flowering and increased flower number. Further transformation of citrus revealed that ethylene and starch content increased, and soluble sugar content decreased in 35S:CiACS4 lemon. Inhibition of CiACS4 in lemon resulted in effects opposite to that of 35S:CiACS4 in transgenic plants. Overexpression of the CiACS4-interacting protein ETHYLENE RESPONSE FACTOR3 (CiERF3) in N. tabacum resulted in delayed flowering and more flowers. Further experiments revealed that the CiACS4-CiERF3 complex can bind the promoters of FLOWERING LOCUS T (CiFT) and GOLDEN2-LIKE (CiFE) and suppress their expression. Moreover, overexpression of CiFE in N. tabacum led to early flowering and decreased flowers, and ethylene, starch, and soluble sugar contents were opposite to those in 35S:CiACS4 transgenic plants. Interestingly, CiFE also bound the promoter of CiFT. Additionally, GA3 and 1-aminocyclopropanecarboxylic acid (ACC) treatments delayed flowering in adult citrus, and treatment with GA and ethylene inhibitors increased flower number. ACC treatment also inhibited the expression of CiFT and CiFE. This study provides a theoretical basis for the application of ethylene to regulate flower number and mitigate the impacts of extreme weather on citrus yield due to delayed flowering.

Evaluation of hydroxymethylfurfural content in commercial and artisanal bee honey from Los Ríos-Babahoyo

Hydroxymethylfurfural (HMF) is a compound that is produced after heat treatment of honey; that is, they are not present in the initial raw materials and can present a potential health hazard; they are known as chemical processing contaminants. This compound is an indicator parameter of the quality of honey produced spontaneously. Its concentration increases with time and other factors, such as improper heat treatment during processing, storage temperature and mode of transportation. The objective of this research is focused on evaluating the content of HMF present in 6 types of bee honey, 3 commercial brands and three artisanal brands; the honey was from eucalyptus and citrus flowering, and the place where the honey was acquired is in the Province of Los Ríos, since being a geographical area with abundant flora, the primary pollinators are bees (Apis Mellifera). In addition, the honey was heated at different temperatures and time intervals to evaluate whether Hydroxymethylfurfural increases when heat is added to the honey. The present work was carried out at the Technical University of Babahoyo; the commercial and artisanal bee honey were acquired between 1 and 5 days before the assay. For HMF analysis, a UV spectrophotometer was used, as specified in INEN 1637 standards, to determine the absorbance of the standard sample at 284 and 336 nm. The HMF values obtained for the three commercial brand honey and the artisanal brand honey are within limits allowed by INEN 1572 Technical Standard, which is 4_mg HMF/100_g of honey (40 mg HMF/kg of honey) as a maximum limit. The mean values ranged from 0.08 to 1.77 mg HMF-/g honey, while the honey subjected to heating had mean values ranging from 0.08 to 4.43 mg HMF/100_g honey. A high HMF content was determined, which exceeded the maximum limit, leading to the conclusion that commercial and artisanal honey does contain Hydroxymethylfurfural. Still, in small quantities, it is important to use good handling and preservation methods to prolong the product's shelf life. Keywords: spectrophotometer ; Apis Mellifera ; radiation

Evaluation of hydroxymethylfurfural content in commercial and artisanal bee honey from Los Ríos-Babahoyo

Hydroxymethylfurfural (HMF) is a compound that is produced after heat treatment of honey; that is, they are not present in the initial raw materials and can present a potential health hazard; they are known as chemical processing contaminants. This compound is an indicator parameter of the quality of honey produced spontaneously. Its concentration increases with time and other factors, such as improper heat treatment during processing, storage temperature and mode of transportation. The objective of this research is focused on evaluating the content of HMF present in 6 types of bee honey, 3 commercial brands and three artisanal brands; the honey was from eucalyptus and citrus flowering, and the place where the honey was acquired is in the Province of Los Ríos, since being a geographical area with abundant flora, the primary pollinators are bees (Apis Mellifera). In addition, the honey was heated at different temperatures and time intervals to evaluate whether Hydroxymethylfurfural increases when heat is added to the honey. The present work was carried out at the Technical University of Babahoyo; the commercial and artisanal bee honey were acquired between 1 and 5 days before the assay. For HMF analysis, a UV spectrophotometer was used, as specified in INEN 1637 standards, to determine the absorbance of the standard sample at 284 and 336 nm. The HMF values obtained for the three commercial brand honey and the artisanal brand honey are within limits allowed by INEN 1572 Technical Standard, which is 4_mg HMF/100_g of honey (40 mg HMF/kg of honey) as a maximum limit. The mean values ranged from 0.08 to 1.77 mg HMF-/g honey, while the honey subjected to heating had mean values ranging from 0.08 to 4.43 mg HMF/100_g honey. A high HMF content was determined, which exceeded the maximum limit, leading to the conclusion that commercial and artisanal honey does contain Hydroxymethylfurfural. Still, in small quantities, it is important to use good handling and preservation methods to prolong the product's shelf life.

A bZIP transcription factor (CiFD) regulates drought- and low-temperature-induced flowering by alternative splicing in citrus.

Drought and low temperature are two key environmental factors that induce adult citrus flowering. However, the underlying regulation mechanism is poorly understood. The bZIP transcription factor FD is a key component of the florigen activation complex (FAC) which is composed of FLOWERING LOCUS T (FT), FD, and 14-3-3 proteins. In this study, isolation and characterization of CiFD in citrus found that there was alternative splicing (AS) of CiFD, forming two different proteins (CiFDα and CiFDβ). Further investigation found that their expression patterns were similar in different tissues of citrus, but the subcellular localization and transcriptional activity were different. Overexpression of the CiFD DNA sequence (CiFD-DNA), CiFDα, or CiFDβ in tobacco and citrus showed early flowering, and CiFD-DNA transgenic plants were the earliest, followed by CiFDβ and CiFDα. Interestingly, CiFDα and CiFDβ were induced by low temperature and drought, respectively. Further analysis showed that CiFDα can form a FAC complex with CiFT, Ci14-3-3, and then bind to the citrus APETALA1 (CiAP1) promoter and promote its expression. However, CiFDβ can directly bind to the CiAP1 promoter independently of CiFT and Ci14-3-3. These results showed that CiFDβ can form a more direct and simplified pathway that is independent of the FAC complex to regulate drought-induced flowering through AS. In addition, a bHLH transcription factor (CibHLH96) binds to CiFD promoter and promotes the expression of CiFD under drought condition. Transgenic analysis found that CibHLH96 can promote flowering in transgenic tobacco. These results suggest that CiFD is involved in drought- and low-temperature-induced citrus flowering through different regulatory patterns.

Colletotrichum abscissum: Detection on symptomless citrus leaves and symptomatic citrus flowers using high‐resolution melting analysis

AbstractHigh‐resolution melting (HRM) analysis has been recently applied for the diagnosis of plant diseases. This cost‐effective method is advantageous over standard PCR as it does not require DNA band visualization or the use of probes necessary for quantitative PCR. Colletotrichum abscissum causes postbloom fruit drop of citrus (PFD) and survives asymptomatically on vegetative tissue. Quiescent appressoria on citrus leaves are the primary source of inoculum between flowering periods. Early PFD symptoms may be misidentified as physical damage on citrus flowers. Our objectives were to validate an HRM‐based method to rapidly identify C. abscissum on citrus leaves and flowers. We screened seven previously published primer pairs and concluded that the most effective set of primers was CaITS‐F and CaITS‐R815. We evaluated three different DNA extraction methods, two with a purification step (DNeasy Plant Mini and PowerSoil kits) and a faster method without a purification step (buffer GEB2). We inoculated citrus leaves with C. abscissum conidial suspensions of varying concentrations and HRM analysis detected as few as 200 C. abscissum spores using DNeasy Plant Mini or DNeasy PowerSoil kits for DNA extraction. As expected, samples extracted with GEB2 buffer reduced HRM sensitivity. We further collected field samples from areas with high and low C. abscissum inoculum levels. The HRM method could detect the pathogen in high inoculum areas from both leaves and flowers regardless of the extraction method used. In summary, we describe a new molecular diagnostic tool to detect C. abscissum on citrus during its asymptomatic and symptomatic stages.

Drought and low temperature-induced NF-YA1 activates FT expression to promote citrus flowering.

Flower induction in adult citrus is mainly regulated by drought and low temperatures. However, the mechanism of FLOWERING LOCUS T regulation of citrus flowering (CiFT) under two flower-inductive stimuli remains largely unclear. In this study, a citrus transcription factor, nuclear factor YA (CiNF-YA1), was found to specifically bind to the CiFT promoter by forming a complex with CiNF-YB2 and CiNF-YC2 to activate CiFT expression. CiNF-YA1 was induced in juvenile citrus by low temperature and drought treatments. Overexpression of CiNF-YA1 increased drought susceptibility in transgenic citrus, whereas suppression of CiNF-YA1 enhanced drought tolerance in silenced citrus plants. Furthermore, a GOLDEN2 - LIKE protein (CiFE) that interacts with CiFT protein was also isolated. Further experimental evidence showed that CiFE binds to the citrus LEAFY (CiLFY) promoter and activates its expression. In addition, the expressions of CiNF-YA1 and CiFE showed a seasonal increase during the floral induction period and were induced by artificial drought and low-temperature treatments at which floral induction occurred. These results indicate that CiNF-YA1 may activate CiFT expression in response to drought and low temperatures by binding to the CiFT promoter. CiFT then forms a complex with CiFE to activate CiLFY, thereby promoting the flowering of adult citrus.

Effects of Water-deficit Stress and Gibberellic Acid on Floral Gene Expression and Floral Determinacy in ‘Washington’ Navel Orange

Effects of water-deficit stress and foliar-applied gibberellic acid (GA3) on ‘Washington’ navel orange (Citrus sinensis) floral gene expression and inflorescence number were quantified. Trees subjected to 8 weeks of water-deficit stress [average stem water potential (SWP) −2.86 MPa] followed by 3 weeks of re-irrigation (SWP recovered to > −1.00 MPa) produced more inflorescences in week 11 than trees well-irrigated (SWP > −1.00 MPa) for the full 11 weeks (P < 0.001). After 8 weeks of water-deficit stress, bud expression of flowering locus t (FT), suppressor of overexpression of constans1 (SOC1), leafy (LFY), apetala1 (AP1), apetala2 (AP2), sepallata1 (SEP1), pistillata (PI), and agamous (AG) increased during the re-irrigation period (weeks 9 and 10), but only AP1, AP2, SEP1, PI, and AG expression increased to levels significantly greater than that of well-irrigated trees. Foliar-applied GA3 (50 mg·L−1) in weeks 2 through 8 of the water-deficit stress treatment did not reduce bud FT, SOC1, or LFY expression, but prevented the upregulation AP1, AP2, SEP1, PI, and AG expression that occurred during re-irrigation in water-deficit stressed trees not treated with GA3. Applications of GA3 to water-deficit stressed trees reduced inflorescence number 95% compared with stressed trees without GA3. Thus, GA3 inhibited citrus (Citrus sp.) floral development in response to water-deficit stress through downregulating AP1 and AP2 expression, which likely led to the failed activation of the downstream floral organ identity genes. The results reported herein suggest that bud determinacy and subsequent floral development in response to water-deficit stress in ‘Washington’ navel orange are controlled by AP1 and AP2 transcript levels, which regulate downstream floral organ identity gene activity and the effect of GA3 on citrus flower formation. The water-deficit stress floral-induction pathway provides an alternative to low-temperature induction that increases the potential for successful flowering in citrus trees grown in areas experiencing warmer, drier winters due to global climate change.

Advances in Citrus Flowering: A Review.

Citrus are polycarpic and evergreen species that flower once in spring or several times a year depending on the genotype and the climatic conditions. Floral induction is triggered by low temperature and water-deficit stress and occurs 2–3 months before bud sprouting, whereas differentiation takes place at the same time as sprouting. The induced buds develop single flowers or determinate inflorescences, so that vegetative growth is required at the axillary buds to renew the polycarpic habit. The presence of fruits inhibits sprouting and flower induction from nearby axillary buds in the current season. In some species and cultivars, this results in low flowering intensity the following spring, thus giving rise to alternate bearing. A number of key flowering genes act in the leaf (CiFT3, CcMADS19, etc.) or in the bud (CsLFY, CsTFL1, etc.) to promote or inhibit both flowering time and reproductive meristem identity in response to these climatic factors, the fruit dominance, or the age of the plant (juvenility). The expression of some of these genes can be modified by gibberellin treatments, which reduce bud sprouting and flowering in adult trees, and constitute the main horticultural technique to control flowering in citrus. This review presents a comprehensive view of all aspects of the flowering process in citrus, converging the research published during the past half century, which focused on plant growth regulators and the nutritional source-sink relationships and guided research toward the study of gene transcription and plant transformation, and the advances made with the development of the tools of molecular biology published during the current century.

The first appearance of the citrus flower moth (Prays citri(Millière, 1873)) (Lepidoptera: Praydidae) in Lithuania

The first appearance of the citrus flower moth (Prays citri(Millière, 1873)) (Lepidoptera: Praydidae) in Lithuania

Functional analysis of a PISTILLATA-like gene CcMADS20 involved in floral organs specification in citrus

PISTILLATA (PI), as a member of MADS-box transcription factor, plays an important role in petal and stamen specification in Arabidopsis. However, little is known about PI-like genes in citrus. To understand the molecular mechanism of PI during the developmental process of citrus flower, a PI-like gene CcMADS20 was isolated from Citrus Clemantina. Sequence alignment and phylogenetic analysis revealed that CcMADS20 had relatively high similarity with PI-like homolog and was classified in the core dicotyledonous group. The temporal and spatial expression analyses showed that CcMADS20 was specifically expressed in petal and stamen of citrus flower, which was consistent with PI expression pattern in Arabidopsis. Protein interaction revealed that CcMADS20 could form heterodimer with AP3-like proteins. Furthermore, ectopic overexpression of CcMADS20 in Arabidopsis resulted in transformation of sepals into petal-like structure, as observed in other plants overexpressing a functional PI-like homolog. Additionally, promoter fragments of CcMADS20 were also cloned in the representative 21 citrus varieties. Interestingly, four types of promoters were discovered in these citrus varieties, resulting from two stable insert/deletion fragments (Locus1 and Locus2). The homo/hetero-zygosity of promoter alleles in each variety was strongly related to the evolutionary origin of citrus. Four promoters activity analysis indicated that Locus1 presence inhibited CcMADS20 transcriptional activity and Locus2 presence promoted its transcriptional activity. These findings suggested that CcMADS20 determines petal and stamen development during the evolutionary process of citrus and four promoters discovered, as effective genetic markers, are valuable for citrus breeding practices.

Embedded Sensing System for Recognizing Citrus Flowers Using Cascaded Fusion YOLOv4-CF + FPGA.

Florescence information monitoring is essential for strengthening orchard management activities, such as flower thinning, fruit protection, and pest control. A lightweight object recognition model using cascade fusion YOLOv4-CF is proposed, which recognizes multi-type objects in their natural environments, such as citrus buds, citrus flowers, and gray mold. The proposed model has an excellent representation capability with an improved cascade fusion network and a multi-scale feature fusion block. Moreover, separable deep convolution blocks were employed to enhance object feature information and reduce model computation. Further, channel shuffling was used to address missing recognition in the dense distribution of object groups. Finally, an embedded sensing system for recognizing citrus flowers was designed by quantitatively applying the proposed YOLOv4-CF model to an FPGA platform. The mAP@.5 of citrus buds, citrus flowers, and gray mold obtained on the server using the proposed YOLOv4-CF model was 95.03%, and the model size of YOLOv4-CF + FPGA was 5.96 MB, which was 74.57% less than the YOLOv4-CF model. The FPGA side had a frame rate of 30 FPS; thus, the embedded sensing system could meet the demands of florescence information in real-time monitoring.

A Comprehensive Thrips Species Assessment for Eco-Consistent Management of Infestations in Mediterranean Citrus Crops

Insects belonging to the Thysanoptera order are an important group of insect pests that require phytosanitary interventions for the protection of citrus crops. This study provides a general and complete overview on the thrips pest species present in citrus orchards in the main countries of the Mediterranean basin. For most species, the distribution areas, host plants, and IPM control methods are provided. The study also presents new data on the status of thrips infestations in three main crops in southern Italy (Calabria), including lemon, bergamot, and orange. The results concern the abundance and the co-occurrence of thrips species in the investigated area. Statistical analysis showed that there were differences between citrus species, canopy exposure, and monitoring period in thrips abundance. In particular, orange species showed the lowest density of thrips present on the plant. Three species, namely Pezothrips kellyanus, Frankliniella occidentalis, and Thrips major, were the most abundant in the monitored area with a marked seasonal increase, especially for the highest density species, P. kellyanus, between March and June. Moreover, for F. occidentalis, the close relationship between its presence on herbaceous flora inside crops and in citrus flowers confirms a thrips interaction with no crops and herbaceous plants and the numerical response of the thrips species. These latest results suggest that wild plants constantly host thrips and therefore an alternative ground cover could be an ecological tool to limit or mitigate the density and damaging activity of thrips populations in citrus crops.

Transcriptomic and physiological analysis reveals interplay between salicylic acid and drought stress in citrus tree floral initiation.

Salicylic acid (SA) and drought stress promote more flowering in sweet orange. The physiological response and molecular mechanism underlying stress-induced floral initiation were discovered by transcriptome profiling. Numerous flowering-regulated genes were identified, and ectopically expressed CsLIP2A promotes early flowering in Arabidopsis. Floral initiation is a critical developmental mechanism associated with external factors, and citrus flowering is mainly regulated by drought stress. However, little is known about the intricate regulatory network involved in stress-induced flowering in citrus. To understand the molecular mechanism of floral initiation in citrus, flower induction was performed on potted Citrus sinensis trees under the combined treatment of salicylic acid (SA) and drought (DR). Physiological analysis revealed that SA treatment significantly normalized the drastic effect of drought stress by increasing antioxidant enzyme activities (SOD, POD, and CAT), relative leaf water content, total chlorophyll, and proline contents and promoting more flowering than drought treatment. Analysis of transcriptome changes in leaves from different treatments showed that 1135, 2728 and 957 differentially expressed genes (DEGs) were revealed in response to DR, SD (SA + DR), and SA (SA + well water) treatments in comparison with the well watered plants, respectively. A total of 2415, 2318 and 1933 DEGs were expressed in DR, SD, and SA in comparison with water recovery, respectively. Some key flowering genes were more highly expressed in SA-treated drought plants than in DR-treated plants. GO enrichment revealed that SA treatment enhances the regulation and growth of meristem activity under drought conditions, but no such a pathway was found to be highly enriched in the control. Furthermore, we focused on various hormones, sugars, starch metabolism, and biosynthesis-related genes. The KEGG analysis demonstrated that DEGs enriched in starch sucrose metabolism and hormonal signal transduction pathways probably account for stress-induced floral initiation in citrus. In addition, a citrus LIPOYLTRANSFERSAE 2A homologous (LIP2A) gene was upregulated by SD treatment. Ectopic expression of CsLIP2A exhibited early flowering in transgenic Arabidopsis. Taken together, this study provides new insight that contributes to citrus tree floral initiation under the SA-drought scenario as well as an excellent reference for stress-induced floral initiation in woody trees.

The Responses of Physiological Characteristics and Flowering Related Gene to the Different Water Stress Levels of Red-Flesh Pummelo Cultivars (Citrus grandis (L.) Osbeck) Own-Rooted by Air Layering Propagation under Two Growing Conditions

One of the major problems in the fruit production of citrus, including pummelo (Citrus grandis) is controlling flowering induction. Water stress is known to be related to flowering induction via physiological responses related to the flowering gene. However, reports on the mechanisms underlying floral induction by water stress in pummelo are limited. Thus, this study aimed to determine the physiological characteristics and the expression of genes related to flowering induction, CiFT (Citrus Flowering locus T), in pummelo at different levels of water stress. Experiments were conducted under two growing conditions: field and container conditions, each using a 2 × 5 factorial experiment in a randomized complete block. Factor A consisted of two red-flesh pummelo cultivars while factor B consisted of five levels of water stress based on the leaf rolling index. Among the seven characteristics studied, only the data of total nitrogen, CiFT, and flower number were combined for analysis due to their results in a homogeneity test. Although a consistent tendency was not observed for the interaction among environments, genotypes, and water stress levels of all characteristics, ‘KKU-105’ grew more flowers under higher water stress conditions (225 flowers). This result may imply that decreases in total nitrogen (1.48%), stomatal conductance (50.53 m−2s−1), chlorophyll fluorescence (0.30 Fv/Fm), and upregulation of CiFT mRNA level (13.95) may induce flowering in the pummelo cultivar ‘KKU-105’.

Research on Lightweight Citrus Flowering Rate Statistical Model Combined with Anchor Frame Clustering Optimization

At present, learning-based citrus blossom recognition models based on deep learning are highly complicated and have a large number of parameters. In order to estimate citrus flower quantities in natural orchards, this study proposes a lightweight citrus flower recognition model based on improved YOLOv4. In order to compress the backbone network, we utilize MobileNetv3 as a feature extractor, combined with deep separable convolution for further acceleration. The Cutout data enhancement method is also introduced to simulate citrus in nature for data enhancement. The test results show that the improved model has an mAP of 84.84%, 22% smaller than that of YOLOv4, and approximately two times faster. Compared with the Faster R-CNN, the improved citrus flower rate statistical model proposed in this study has the advantages of less memory usage and fast detection speed under the premise of ensuring a certain accuracy. Therefore, our solution can be used as a reference for the edge detection of citrus flowering.