The Ecophysiological Response of Olive Trees under Different Fruit Loads.

Olive trees have a unique reproductive pattern marked by biennial fruiting. This study examined the repercussions of alternate fruit bearing on the water relations of olive trees and the associated ecophysiological mechanisms. The experiment spanned two consecutive years: the "ON" year, characterized by a high crop load, and the "OFF" year, marked by minimal fruit production. Key ecophysiological parameters, including sap flow, stomatal conductance, and photosynthetic rate, were monitored in both years. Pre-dawn water potential was measured using continuous stem psychrometers and the pressure chamber technique. Biochemical analyses focused on non-structural carbohydrate concentrations (starch, sucrose, and mannitol) and olive leaves' carbon-stable isotope ratio (δ13C). Results revealed a higher leaf gas exchange rate during the "ON" year, leading to an average 29.3% increase in water consumption and a 40.78% rise in the photosynthetic rate. Higher water usage during the "ON" year resulted in significantly lower (43.22% on average) leaf water potential. Sucrose and starch concentrations were also increased in the "ON" year, while there were no significant differences in mannitol concentration. Regarding the carbon-stable isotope ratio, leaves from the "OFF" year exhibited significantly higher δ13C values, suggesting a higher resistance to the CO2 pathway from the atmosphere to carboxylation sites compared to the "ON" year plants.

Citrus Pruning in the Mediterranean Climate: A Review.

Pruning is a common practice in citrus for various reasons. These include controlling and shaping the canopy; improving phytosanitary health, productivity, and fruit quality; and facilitating operations such as harvesting and phytosanitary treatments. Because pruning is an expensive operation, its need is sometimes questioned. However, it has been proven to be particularly important in Mediterranean citriculture, which is oriented towards producing fruits for a high-quality demanding fresh market. Herein, we summarize and explain the pruning techniques used in Mediterranean citriculture and refer to the main purposes of each pruning type, considering citrus morphology and physiology.

Interactive effect of branch source-sink ratio and leaf aging on photosynthesis in pistachio.

Tree source-sink ratio has a predominant and complex impact on tree performance and can affect multiple physiological processes including vegetative and reproductive growth, water and nutrient use, photosynthesis, and productivity. In this study, we manipulated the branch level source-sink ratio by reduction of photosynthetic activity (partial branch defoliation) or thinning branch fruit load early in the growing season (after fruit set) in pistachio (Pistacia vera) trees. We then characterized the leaf photosynthetic light response curves through leaf aging. In addition, we determined changes in leaf non-structural carbohydrates (NSC) and nitrogen (N) concentrations. In leaves with high source-sink ratios, there was a gradual decrease in maximum net photosynthetic rate (ANmax) over the growing season, while in branches with low source-sink ratios, there was a sharp decline in ANmax in the first two weeks of August. Branches with high-sink showed an up-regulation (increase) in photosynthesis toward the end of July (at 1,500 growing degree days) during the period of rapid kernel growth rate and increased sink strength, with ANmax being about 7 µmol m-1 s-1 higher than in branches with low-sink. In August, low source-sink ratios precipitated leaf senescence, resulting in a drastic ANmax decline, from 25 to 8 µmol m-1 s-1 (70% drop in two weeks). This reduction was associated with the accumulation of NSC in the leaves from 20 to 30 mg g-1. The mechanisms of ANmax reduction differ between the two treatments. Lower photosynthetic rates of 8-10 µmol m-1 s-1 late in the season were associated with lower N levels in high-sink branches, suggesting N remobilization to the kernels. Lower photosynthesis late in the season was associated with lower respiration rates in low-source branches, indicating prioritization of assimilates to storage. These results can facilitate the adaptation of management practices to tree crop load changes in alternate bearing species.

Modeling and prediction of phase shifts in noisy two-cycle oscillations.

Understanding and predicting ecological dynamics in the presence of noise remains a substantial and important challenge. This is particularly true in light of the poor quality of much ecological data and the imprecision of many ecological models. As a first approach to this problem, we focus here on a simple system expressed as a discrete time model with 2-cycle behavior, reflecting alternating high and low population sizes. Such dynamics naturally arise in ecological systems with overcompensatory density dependence. We ask how the amount of detail included in the population estimates affects the ability to forecast the likelihood of changes in the phase of oscillation, meaning whether high populations occur in odd or in even years. We adjust the level of detail by converting continuous population levels to simple, coarse-grained descriptions using two-state and four-state models. We also consider a cubic noisy over-compensatory model with three parameters. The focus on phase changes is what distinguishes the question we are asking and the methods we use from more standard time series approaches. Obviously, adding observation states improves the ability to forecast phase shifts. In particular, the four-state model and cubic model outperform the two-state model because they include a transition state, through which the dynamics typically pass during a phase change. Nonetheless, at high noise levels the improvement in forecast skill is relatively modest. Additionally, the frequency of phase changes depends strongly on the noise level, and is much less affected by the parameter determining amplitude in the population model, so phase shift frequencies could possibly be used to infer noise levels.

Co-regulatory effects of hormone and mRNA-miRNA module on flower bud formation of Camellia oleifera.

Few flower buds in a high-yield year are the main factors restricting the yield of Camellia oleifera in the next year. However, there are no relevant reports on the regulation mechanism of flower bud formation. In this study, hormones, mRNAs, and miRNAs were tested during flower bud formation in MY3 ("Min Yu 3," with stable yield in different years) and QY2 ("Qian Yu 2," with less flower bud formation in a high-yield year) cultivars. The results showed that except for IAA, the hormone contents of GA3, ABA, tZ, JA, and SA in the buds were higher than those in the fruit, and the contents of all hormones in the buds were higher than those in the adjacent tissues. This excluded the effect of hormones produced from the fruit on flower bud formation. The difference in hormones showed that 21-30 April was the critical period for flower bud formation in C. oleifera; the JA content in MY3 was higher than that in QY2, but a lower concentration of GA3 contributed to the formation of the C. oleifera flower bud. JA and GA3 might have different effects on flower bud formation. Comprehensive analysis of the RNA-seq data showed that differentially expressed genes were notably enriched in hormone signal transduction and the circadian system. Flower bud formation in MY3 was induced through the plant hormone receptor TIR1 (transport inhibitor response 1) of the IAA signaling pathway, the miR535-GID1c module of the GA signaling pathway, and the miR395-JAZ module of the JA signaling pathway. In addition, the expression of core clock components GI (GIGANTEA) and CO (CONSTANS) in MY3 increased 2.3-fold and 1.8-fold over that in QY2, respectively, indicating that the circadian system also played a role in promoting flower bud formation in MY3. Finally, the hormone signaling pathway and circadian system transmitted flowering signals to the floral meristem characteristic genes LFY (LEAFY) and AP1 (APETALA 1) via FT (FLOWERING LOCUS T) and SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CO 1) to regulate flower bud formation. These data will provide the basis for understanding the mechanism of flower bud alternate formation and formulating high yield regulation measures for C. oleifera.

Advancing tree genomics to future proof next generation orchard production.

The challenges facing tree orchard production in the coming years will be largely driven by changes in the climate affecting the sustainability of farming practices in specific geographical regions. Identifying key traits that enable tree crops to modify their growth to varying environmental conditions and taking advantage of new crop improvement opportunities and technologies will ensure the tree crop industry remains viable and profitable into the future. In this review article we 1) outline climate and sustainability challenges relevant to horticultural tree crop industries, 2) describe key tree crop traits targeted for improvement in agroecosystem productivity and resilience to environmental change, and 3) discuss existing and emerging genomic technologies that provide opportunities for industries to future proof the next generation of orchards.

Expression Profiling of Four Mango FT/TFL1-Encoding Genes under Different Fruit Load Conditions, and Their Involvement in Flowering Regulation.

Plant flowering is antagonistically modulated by similar FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1) proteins. In mango (Mangifera indica L.), flowering is induced by cold temperatures, unless the tree is juvenile or the adult tree had a high fruit load (HFL) in the summer. Here, we studied the effects of juvenility and fruit load on the expression of four MiFT/TFL1 genes cloned from the mango 'Shelly' cultivar. Ectopic expression of MiFT1 in Arabidopsis resulted in early flowering, whereas over-expression of MiFT2 and the two cloned MiTFL1 genes repressed flowering. Moreover, juvenility was positively correlated with higher transcript levels of MiFT2 and both MiTFL1s. In trees with a low fruit load, leaf MiFT1 expression increased in winter, whereas HFL delayed its upregulation. MiFT2 expression was upregulated in both leaves and buds under both fruit load conditions. Downregulation of both MITFL1s in buds was associated with a decrease in regional temperatures under both conditions; nevertheless, HFL delayed the decrease in their accumulation. Our results suggest that cold temperature has opposite effects on the expression of MiFT1 and the MiTFL1s, thereby inducing flowering, whereas HFL represses flowering by both suppressing MiFT1 upregulation and delaying MiTFL1s downregulation. The apparent flowering-inhibitory functions of MiFT2 are discussed.

Profiling of phytohormones in apple fruit and buds regarding their role as potential regulators of flower bud formation.

Apple (Malus × domestica Borkh.) cropping behavior, if not regulated, is often manifested by high yields of small-sized fruit in so called ON-years, which are usually followed by strongly reduced crop loads in OFF-years. Such cropping pattern is defined as biennial bearing and causes significant losses in apple production. The growth of apple fruit overlaps with the formation of flower buds, which remain dormant until the following spring. Earlier works proposed that some fruit-derived mobile compounds, as e.g., phytohormones, could suppress flower bud formation that thereby leads to biennial bearing. We addressed this hypothesis by analyzing 39 phytohormones in apple seeds, fruit flesh and by measuring phytohormone export from the fruits of the biennial bearing cultivar 'Fuji' and of the regular bearing cultivar 'Gala'. Moreover, we analyzed the same compounds in bourse buds from fruiting (ON-trees) and non-fruiting (OFF-trees) spurs of both apple cultivars over the period of flower bud formation. Our results showed that apple fruit exported at least 14 phytohormones including indole-3-acetic acid and gibberellin A3; however, their influence on flower bud formation was inconclusive. A gibberellin-like compound, which was detected exclusively in bourse buds, was significantly more abundant in bourse buds from ON-trees compared with OFF-trees. Cultivar differences were marked by the accumulation of trans-zeatin-O-glucoside in bourse buds of 'Gala' ON-trees, whereas the levels of this compound in 'Gala' OFF were significantly lower and comparable to those in 'Fuji' ON- and OFF-trees. Particular phytohormones including five cytokinin forms as well as abscisic acid and its degradation products had higher levels in bourse buds from OFF-trees compared with ON-trees and were therefore proposed as potential promotors of flower bud initiation. The work discusses regulatory roles of phytohormones in flower bud formation in apple based on the novel and to date most comprehensive phytohormone profiles of apple fruit and buds.

Reversion of fruit-dependent inhibition of flowering in Citrus requires sprouting of buds with epigenetically silenced CcMADS19.

In Citrus, the response to environmental floral inductive signals is inhibited by the presence of developing fruits. The mechanism involves epigenetic activation of the CcMADS19 locus (FLC orthologue), encoding a floral repressor. To understand how this epigenetic regulation is reverted to allow flowering in the following season, we have forced precocious sprouting of axillary buds in fruit-bearing shoots, and examined the competence to floral inductive signals of old and new leaves derived from them. We have found that CcMADS19 is enriched in repressive H3K27me3 marks in young, but not old leaves, revealing that axillary buds retain a silenced version of the floral repressor that is mitotically transmitted to the newly emerging leaves, which are able to induce flowering. Therefore, we propose that flowering in Citrus is necessarily preceded by vegetative sprouting, so that the competence to respond to floral inductive signals is reset in the new leaves.

Proteomic differences in apple spur buds from high and non-cropping trees during floral initiation.

The cropping behavior of biennial apple (Malus ×domestica Borkh.) cultivars is irregular and often follows a biennial bearing pattern with 'On' years (high crop load and inhibited floral bud formation) followed by 'Off' years (little crop load and a promoted formation of floral buds). To study proteomic differences between floral and vegetative buds, trees of the strongly alternating cultivar 'Fuji' and the regular bearing cultivar 'Gala' were either completely thinned or not thinned at full bloom to establish two cropping treatments with no ('Off') or a high ('On') crop load, respectively. Student's t-Tests indicated significant differences of protein profiles in buds from 2-year old spurs from both treatments at each sampling date. Abundance patterns of protein clusters coincided with the onset of floral bud initiation and were most noticeable in buds from 'On' trees with a decreased abundance of key enzymes of the phenylpropanoid and flavonoid pathways and an increased abundance of histone deacetylase and ferritins. Furthermore, an increased abundance of proteins involved in histone and DNA methylation was found in the buds from 'Off' trees. This study presents the first large-scale, label-free proteomic profiling of floral and vegetative apple buds during the period of floral bud initiation. SIGNIFICANCE: Although several studies exist that address the complex developmental processes associated with the formation of floral buds in apple (Malus ×domestica Borkh.) at transcriptomic level, no data is available for explaining the difference between floral and vegetative buds or biennial and regular bearing cultivars on a proteomic level. This study presents the first large-scale, label-free proteomic profiling of floral and vegetative apple buds from the two cultivars 'Fuji' and 'Royal Gala' during the period of floral bud initiation and renders possible the development of suitable biomarkers for biennial bearing in apple.

Comparative transcriptomics in alternate bearing cultivar Dashehari reveals the genetic model of flowering in mango.

Flowering is a complex developmental process, with physiological and morphological phases influenced by a variety of external and internal factors. Interestingly, many mango cultivars tend to bear fruit biennially because of irregular flowering, and this has a negative impact on mango flowering and the subsequent yield, resulting in significant economic losses. In this article, transcriptome analysis was carried out on four tissues of mango cv. Dashehari (bearing tree leaf, shoot apex, inflorescence, and non-bearing tree leaf). De novo transcriptome assembly of RNA-seq reads of Dashehari using the Trinity pipeline generated 67,915 transcripts, with 25,776 genes identified. 85 flowering genes, represented by 179 transcripts, were differentially expressed in bearing vs. non-bearing leaf tissues. Gene set enrichment analysis of flowering genes identified significant upregulation of flowering related genes in inflorescence tissues compared to bearing leaf tissues. The flowering genes FT, CO, GI, ELF 4, FLD, FCA, AP1, LHY, and SCO1 were upregulated in the bearing leaf tissues. Pathway analysis of DEGs showed significant upregulation of phenylpropanoid and sucrose and starch pathways in non-bearing leaf tissue compared with bearing leaf tissue. The comparative transcriptome analysis performed in this study significantly increases the understanding of the molecular mechanisms driving the flowering process as well as alternative bearing in mango.

By wind or wing: pollination syndromes and alternate bearing in horticultural systems.

Cyclical fluctuations in reproductive output are widespread among perennial plants, from multi-year masting cycles in forest trees to alternate bearing in horticultural crops. In natural systems, ecological drivers such as climate and pollen limitation can result in synchrony among plants. Agricultural practices are generally assumed to outweigh ecological drivers that might synchronize alternate-bearing individuals, but this assumption has not been rigorously assessed and little is known about the role of pollen limitation as a driver of synchrony in alternate-bearing crops. We tested whether alternate-bearing perennial crops show signs of alternate bearing at a national scale and whether the magnitude of national-scale alternate bearing differs across pollination syndromes. We analysed the Food and Agriculture Organization of the United Nations time series (1961-2018) of national crop yields across the top-producing countries of 27 alternate-bearing taxa, 6 wind-pollinated and 21 insect-pollinated. Alternate bearing was common in these national data and more pronounced in wind-pollinated taxa, which exhibited a more negative lag-1 autocorrelation and a higher coefficient of variation (CV). We highlight the mutual benefits of integrating ecological theory and agricultural data for (i) advancing our understanding of perennial plant reproduction across time, space and taxa, and (ii) promoting stable farmer livelihoods and global food supply. This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.

Defining date palm leaf pruning line in bearing status by tracking physiological markers and expression of senescence-related genes.

The physiological and molecular markers were evaluated for defining leaf pruning line in bearing status of date palm (Phoenix dactylifera cv. Mazafati). Our results showed that the higher expression of the chlorophyllase (Chlase) gene was concomitant with lower expression of chlorophyll synthase (ChlG) and oxygen-evolving enhancer protein (PSBO) genes in the 6-year-old leaf line. In addition, the 6-year-old leaf line resulted in a lower Hill reaction rate, chlorophyll a/b ratio, photosystem Ⅱ quantum efficiency, and photosynthesis rate. Also, lower expression and activities of catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) was associated with higher malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation in 6-year-old leaf line. These results suggested that the physiological maturity termination, senescence stage initiation, and source to sink transition could occur in 6-year-old leaves. Furthermore, delayed 5-year-old leaf pruning line adjustment in consecutive years could increase quantitative and qualitative yield loss, decrease water use efficiency, and promote alternate bearing and fruit abscission, which is considered a common problem of date growing areas. Further, the senescence-related markers in the alternate bearing trees pruned in pruning line 5 showed a tendency to normal trees. The five-year-old pruning line also resulted in the balance of bunching and loading the alternate bearing trees.

A Complex Gene Network Mediated by Ethylene Signal Transduction TFs Defines the Flower Induction and Differentiation in Olea europaea L.

The olive tree (Olea europaea L.) is a typical Mediterranean crop, important for olive and oil production. The high tendency to bear fruits in an uneven manner, defined as irregular or alternate bearing, results in a significant economic impact for the high losses in olives and oil production. Buds from heavy loaded ('ON') and unloaded ('OFF') branches of a unique olive tree were collected in July and the next March to compare the transcriptomic profiles and get deep insight into the molecular mechanisms regulating floral induction and differentiation. A wide set of DEGs related to ethylene TFs and to hormonal, sugar, and phenylpropanoid pathways was identified in buds collected from 'OFF' branches. These genes could directly and indirectly modulate different pathways, suggesting their key role during the lateral bud transition to flowering stage. Interestingly, several genes related to the flowering process appeared as over-expressed in buds from March 'OFF' branches and they could address the buds towards flower differentiation. By this approach, interesting candidate genes related to the switch from vegetative to reproductive stages were detected and analyzed. The functional analysis of these genes will provide tools for developing breeding programs to obtain olive trees characterized by more constant productivity over the years.

Alternate bearing in fruit trees: fruit presence induces polar auxin transport in citrus and olive stem and represses IAA release from the bud.

In many fruit trees, heavy fruit load in one year reduces flowering in the following year, creating a biennial fluctuation in yield termed alternate bearing (AB). In subtropical trees, where flowering induction is mostly governed by the accumulation of chilling hours, fruit load is thought to generate a signal (AB signal) that blocks the perception of cold induction. Fruit removal during a heavy-fruit-load year is effective at inducing flowering only if performed one to a few months before the onset of the flowering induction period. We previously showed that following fruit removal, the content of the auxin indoleacetic acid (IAA) in citrus buds is reduced, suggesting that the hormone plays a role in the AB signal. Here, we demonstrate that fruit presence generates relatively strong polar auxin transport in citrus and olive stems. Upon fruit removal, polar auxin transport is reduced and allows auxin release from the bud. Furthermore, using immunolocalization, hormone, and gene expression analyses, we show that in citrus, IAA level in the bud and specifically in the apical meristem is reduced upon fruit removal. Overall, our data provide support for the notion that fruit presence generates an auxin signal in the bud, which may affect flowering induction.

Transcriptomic Analysis of the Pistacia vera (L.) Fruits Enable the Identification of Genes and Hormone-Related Gene Linked to Inflorescence Bud Abscission.

Pistacia vera (L.) is an alternate bearing species. The tree produces axillary inflorescence buds every year. Still, they abscise in "ON" overloaded shoots, causing a limited production in the following "OFF" year, causing a significant and unfavorable production fluctuation. In this work, we carried out de novo discovery and transcriptomic analysis in fruits of "ON" and "OFF" shoots of the cultivar Bianca. We also investigated whether the fruit signaling pathway and hormone biosynthesis directly or indirectly linked to the premature fall of the inflorescence buds causing alternate bearing. We identified 1536 differentially expressed genes (DEGs) in fruits of "ON" vs. "OFF" shoots, which are involved primarily in sugar metabolism, plant hormone pathways and transcription factors. The premature bud abscission linked to the phenomenon is attributable to a lack of nutrients (primarily sugar) and the possible competition between the same branches' sinks (fruits vs. inflorescence buds). Hormone pathways are involved as a response to signals degradation and remobilization of carbon and nutrients due to the strengthening of the developing embryos. Genes of the secondary metabolism and transcription factors are also involved in tailoring the individual branches response to the nutritional stress and sink competition. Crosstalk among sugar and various hormone-related genes, e.g., ethylene, auxin, ABA and cytokinin, were determined. The discovery of putative biomarkers like callose synthase 5, trehalose-6-phosphate synthase, NAD(P)-linked oxidoreductase and MIOX2, Jasmonate, and salicylic acid-related genes can help to design precision farming practices to mitigate the alternate bearing phenomenon to increase farming profitability. The aim of the analysis is to provide insight into the gene expression profiling of the fate of "ON" and "OFF" fruits associated with the alternate bearing in the pistachio.

Transcriptome Analysis of Pistacia vera Inflorescence Buds in Bearing and Non-Bearing Shoots Reveals the Molecular Mechanism Causing Premature Flower Bud Abscission.

The alteration of heavy ("ON/bearing") and light ("OFF/non-bearing") yield in pistachio (Pistacia vera L.) has been reported to result from the abscission of inflorescence buds on high yielding trees during the summer, but the regulatory mechanisms involved in this bud abscission remain unclear. The analysis provides insights into the transcript changes between inflorescence buds on bearing and non-bearing shoots, that we indicated as "ON" and "OFF", and shed light on the molecular mechanisms causing premature inflorescence bud abscission in the pistachio cultivar "Bianca" which can be related to the alternate bearing behavior. In this study, a transcriptome analysis was performed in inflorescence buds of "ON" and "OFF" shoots. A total of 14,330 differentially expressed genes (DEGs), most of which are involved in sugar metabolism, plant hormone pathways, secondary metabolism and oxidative stress pathway, were identified. Our results shed light on the molecular mechanisms underlying inflorescence bud abscission in pistachio and we proposed a hypothetical model behind the molecular mechanism causing this abscission in "ON" shoots. Results highlighted how changes in genes expressed in nutrient pathways (carbohydrates and mineral elements) in pistachio "ON" vs. "OFF" inflorescence buds triggers a cascade of events involving trehalose-6-phosphate and target of rapamycin (TOR) signaling, SnRK1 complex, hormones, polyamines and ROS which end, through programmed cell death and autophagy phenomena, with the abscission of inflorescence buds. This is the first study reporting gene expression profiling of the fate of "ON" and "OFF" inflorescence buds associated with the alternate bearing in the pistachio.

Comparative RNA sequencing based transcriptome profiling of regular bearing and alternate bearing mango (Mangifera indica L.) varieties reveals novel insights into the regulatory mechanisms underlying alternate bearing.

OBJECTIVE: This study is to understand a comprehensive perspective on the molecular mechanisms underlying alternate bearing in mango (Mangifera indica L.) via transcriptome wide gene expression profiling of both regular and irregular mango varieties. RESULTS: Transcriptome data of regular (Neelam) and irregular (Dashehari) mango varieties revealed a total of 42,397 genes. Out of that 12,557 significantly differentially expressed genes were identified, of which 6453 were found to be up-regulated and 6104 were found to be down-regulated genes. Further, many of the common unigenes which were involved in hormonal regulation, metabolic processes, oxidative stress, ion homeostasis, alternate bearing etc. showed significant differences between these two different bearing habit varieties. Pathway analysis showed the highest numbers of differentially expressed genes were related with the metabolic processes (523). A total of 26 alternate bearing genes were identified and principally three genes viz; SPL-like gene (GBVX01015803.1), Rumani GA-20-oxidase-like gene (GBVX01019650.1) and LOC103420644 (GBVX01016070.1) were significantly differentially expressed (at log2FC and pval less than 0.05) while, only single gene (gbGBVW01004309.1) related with flowering was found to be differentially expressed. A total of 15 differentially expressed genes from three important pathways viz; alternate bearing, carbohydrate metabolism and hormone synthesis were validated using Real time PCR and results were at par with in silico analysis. CONCLUSIONS: Deciphering the differentially expressed genes (DEGs) and potential candidate genes associated with alternate bearing, hormone and carbohydrate metabolism pathways will help for illustrating the molecular mechanisms underlying the bearing tendencies in mango.

Fruit-dependent epigenetic regulation of flowering in Citrus.

In many perennial plants, seasonal flowering is primarily controlled by environmental conditions, but in certain polycarpic plants, environmental signals are locally gated by the presence of developing fruits initiated in the previous season through an unknown mechanism. Polycarpy is defined as the ability of plants to undergo several rounds of reproduction during their lifetime, alternating vegetative and reproductive meristems in the same individual. To understand how fruits regulate flowering in polycarpic plants, we focused on alternate bearing in Citrus trees that had been experimentally established as fully flowering or nonflowering. We found that the presence of the fruit causes epigenetic changes correlating with the induction of the CcMADS19 floral repressor, which prevents the activation of the floral promoter CiFT2 even in the presence of the floral inductive signals. By contrast, newly emerging shoots display an opposite epigenetic scenario associated with CcMADS19 repression, thereby allowing the activation of CiFT2 the following cold season.