A forum for discussion of potential collaborations with regards to fruit, vegetable, and edible crops – i.e. citrus, breeding, production systems, postharvest, pomology, crop management, viticulture, etc.
I work with peri-urban vegetable production, saffron production and roadside vegetation for southern New England. I am the Vice-President Elect for Extension.
Freezing temperatures is a significant threat to new growing fresh market citrus industry in North Florida, causing big damage to young and established groves. Recent freeze event happened December 2022 caused about 95% loss in fruit yield in southeast citrus comprising of North Florida, South Georgia and Southeastern Alabama. Different physiological, biochemical and molecular factors are associated with freezing tolerance in citrus. The present study investigates the effects of various cold acclimation periods on freezing tolerance of Valencia orange grafted onto two commercial rootstocks i.e., US-942 and C-54. The plants were cold acclimatized at 4°C for 4, 8, 16 and 32 hours and shifted to the programmed cold chamber for freezing stress at -6°C The Valencia plants on both rootstocks exhibited enhanced resistance to freezing stress when cold acclimated at 4°Cfor 16- and 32-hour . The antioxidants enzymatic activities [superoxide dismutase (EC 1.15.1.1), peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), and ascorbate peroxidase (EC 1.11.1.11)], and carbohydrate metabolic enzymes showed higher activity in response to cold acclimation for 16- and 32-hour. Likewise, osmoprotectants accumulation (proline and glycine betaine), and soluble sugars (glucose, fructose, sucrose, starch, and total soluble solids) were also elevated under when cold acclimated for 16- and 32-hour as compared to the control. The freezing susceptibility was higher in control and 4-hour cold acclimated plants. Overall, the acclimation period of 16 hours found to very effective in improving freezing tolerance than all other acclimation periods. Findings of this study provides valuable insights into optimizing acclimation strategies to improve cold hardiness in citrus and potential platform for further research to use at commercial level.
Citrus, a globally significant fruit crop, is rich in nutrients and vitamins but is adversely affected by environmental stresses, particularly drought. Drought stress hinders plant growth and reduces crop yields. This study focused on sour orange (SO) and trifoliate orange (TO) rootstocks to evaluate their performance under control and drought conditions. Transcriptomic results showed that the control vs drought TO have 3620 differentially expressed genes (DEGs) were down-regulated and 2440 genes were upregulated while the control vs drought SO group showed 3625 genes were down-regulated and 2290 genes were upregulated. Most of the DEGs were associated with different molecular functions and biological processes including metabolic pathways, flavonoids biosynthesis, photosynthesis, and glutathione metabolism in both rootstocks under drought; however, the gene expression analysis showed that the expression of flavonoids and glutathione metabolism genes were higher in SO than TO after 12 days of drought stress (12DS). Moreover, the antioxidative enzymes, free radical scavenging activities, and total flavonoids contents were increased in both rootstocks, but the increase was higher in SO than TO, after 12DS. After 12DS, the TO has significantly higher levels of reactive oxygen species, hydrogen peroxide, electrolytic leakage, and malondialdehyde contents than SO. Our study concluded that SO rootstock enhances genes linked to metabolic pathways, flavonoid biosynthesis, photosynthesis, and glutathione metabolism. It also, boosts antioxidant enzyme activities, antioxidant capacity, and flavonoid levels, while effectively neutralizing the reactive oxygen species. Hence, after 12 days of drought stress, sour orange performs better than trifoliate orange in maintaining these protective mechanisms.
Climate change-induced abiotic stresses, particularly drought and freezing, threaten citrus production worldwide. Understanding how drought priming enhances cold hardiness is pivotal for sustaining grapefruit (Citrus paradisi) production under increasingly unpredictable climatic conditions. This study employed an integrative approach combining transcriptomic and metabolomic profiling and physiological and morphological observations to unravel the complex regulatory networks underlying drought-primed freezing tolerance in grapefruit plants. Drought-primed plants exhibited significantly improved photosynthetic efficiency, as measured by chlorophyll fluorescence and gas exchange parameters, and remained higher in primed plants under freezing stress. Scanning Electron Microscopy (SEM) revealed ultrastructural changes, including intact stomatal architecture and less plasmolysis in leaf tissues of drought-primed plants. Transcriptome analysis revealed a distinct reprogramming of stress-responsive genes, particularly those involved in transcriptional regulation and hormone signaling pathways. Notably, genes encoding transcription factors such as DREB, NAC, and WRKY showed marked upregulation in primed plants. Metabolomic profiling complemented these findings by identifying key metabolic shifts, including accumulating compatible solutes (e.g., proline, sugars) and modulation of central carbon metabolism and amino acid biosynthesis pathways. Hormonal analysis indicated a synergistic interaction between abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA), suggesting their critical roles in stress signal integration. Our results demonstrate that drought priming activates a robust transcriptional-metabolic network, enhancing physiological resilience and structural integrity under freezing stress. This study provides novel insights into the cross-adaptive mechanisms of abiotic stress tolerance and establishes a foundational framework for developing climate-resilient citrus cultivars.
Freezing tolerance is a critical factor affecting the productivity and sustainability of citrus cultivation in subtropical regions. Photoperiod and cold acclimation work together to enhance a plant’s freezing tolerance by triggering specific biochemical and molecular pathways that help it withstand low temperatures and avoid cellular damage during freezing events. This study aims to investigate the interactive effects of photoperiod and cold acclimation on the freezing tolerance of Valencia orange (Citrus sinensis) plants grafted onto US942 rootstock, focusing on how these environmental factors modulate physiological and molecular responses to freezing stress. We hypothesize that varying photoperiods, when combined with cold acclimation, will synergistically enhance the freezing tolerance of Valencia orange plants by modulating biochemical and physiological traits associated with cold hardiness. Two-year-old Valencia orange plants will be grown under different photoperiods (8, 10, 12, 14, and 16 hours) for four weeks. After the photoperiod treatment, plants from each photoperiod group were divided into two treatments: one group undergo cold acclimation by being exposed to 4°C for 16 hours, while the other group was placed at 25°C for 16 hours (non-cold-acclimated). Following this, both cold-acclimated and non-cold-acclimated plants were exposed to freezing stress at -6°C in walk-in freezing chambers for 1 hour. The freezing temperature reached by gradually lowering the temperature by 1°C per hour, starting from 0°C to -6°C. We measured the photosynthesis, chlorophyll content and ELL. These results showed that the freezing stress showed the photosynthesis limitation, there are problem in enzymatic machinery in carbon dioxide assimilation. According to ELL and spad index GBT3R2 shows lowest cellular damage and the results show preserved the chlorophyll content. This research identifies how photoperiods and cold acclimation interact to enhance freezing tolerance in Valencia oranges, providing key markers for breeding more freeze resilient citrus cultivars.
The study was conducted at the Southwest Florida Research and Education Center (SWFREC), University of Florida (UF), between 2012 and 2013. It focused on evaluating oxidative stress metabolism in two-year-old 'Valencia' sweet orange (Citrus sinensis) plants grafted onto Swingle rootstock (Citrus paradisi × Poncirus trifoliata). Both healthy and HLB-affected plants were cultivated under controlled greenhouse conditions. Leaf samples, ranging from young to fully expanded stages, were analyzed to observe biochemical responses to HLB infection. Early-stage HLB-affected leaves appeared asymptomatic but later developed blotchy patterns, characteristic of the disease. Hydrogen peroxide (H₂O₂) levels increased in both healthy and HLB-affected leaves, with significantly higher concentrations observed in the latter. Healthy leaves showed H₂O₂ levels ranging from 0.5 to 3.8 µmole per gram of fresh weight (FW), while affected leaves exhibited levels from 0.56 to 6.5 µmole per gram FW, especially in fully expanded leaves. Enzymatic activities related to oxidative stress were also evaluated. Catalase (CAT) and ascorbate peroxidase (APX) activities increased during the leaf expansion phase but declined in fully expanded leaves, with a sharper decrease observed in HLB-affected samples. The reduced CAT and APX activity in affected leaves contributed to the accumulation of H₂O₂, exacerbating oxidative stress. Guaiacol peroxidase (GPOD) activity was low during early leaf expansion but increased in fully expanded leaves. HLB-affected leaves showed significantly higher GPOD activity, possibly contributing to elevated H₂O₂ levels. Glutathione reductase (GR) activity, vital for maintaining redox balance by regenerating reduced glutathione (GSH), was higher in healthy leaves but declined in HLB-affected samples. This decline suggested impaired recycling of GSH, disrupting redox homeostasis and weakening antioxidant defenses. In contrast, glutathione-S-transferase (GST) activity was elevated in HLB-affected leaves, likely as an adaptive response to detoxify reactive oxygen species (ROS). However, the combination of increased GST and reduced GR activity led to a depletion of reduced glutathione, further intensifying oxidative stress. Overall, the study highlights the disruption of oxidative stress metabolism in HLB-affected sweet orange leaves. The compromised antioxidant defense system, characterized by reduced CAT, APX, and GR activities, contributes to increased cellular damage. These findings provide insights into plant defense mechanisms and suggest potential intervention strategies for managing HLB-induced stress.
The citrus industry in Florida has been decimated by huanglongbing (HLB), a disease vectored by the Asian citrus psyllid. Industry standard budlines of sweet orange in Florida have all been deemed susceptible to HLB and do not produce profitable yields at the vast majority of commercial groves. Symptoms of HLB include low yield, premature fruit drop, stunted growth, poor fruit and juice quality, blotchy mottle of leaf tissue, and eventual tree decline, dieback, and tree death. There is not yet a therapy or treatment that has cured this disease. A relatively new selection of sweet orange called 'OLL-8' has shown increased tolerance to HLB as measured by yield, fruit quality, tree growth and multispectral imaging metrics. The 'OLL' acronym represents the names of Orie and Louise Lee, who were citrus farmers in the State of Florida for decades. The 'OLL-8' sweet orange is a somaclone of the original 'OLL' tree that was found in St. Cloud, FL. Evidence of the enhanced tolerance of OLL-8 versus standard 'Valencia' and 'Hamlin' will be presented in the form of fruit and juice quality, yield, tree growth and size, and multispectral drone imagery data, including normalized difference vegetation index (NDVI). The 'OLL-8' sweet orange outperformed both conventional scions at multiple sites over multiple seasons in Polk County FL. Several drone flights were used to determine tree size and health over time. The results demonstrate the possibility of enhanced plant performance with the use of somaclonal variation in sweet orange in the HLB environment. More research is needed to confirm 'OLL-8' sweet orange's tolerance, and if confirmed, the biological mechanisms of this budline's tolerance could be elucidated for developing more HLB tolerant germplasm via conventional breeding or biotechnological methods.
Funding Source USDA Agricultural Marketing Service (AMS) MultiState Specialty Crop Block Grant through the California Department of Food and Agriculture project number 19-1043-002-SF
Industrial processing of citrus fruits produces tons of peel, pulp, and seeds as by-products. Although currently considered waste, these byproducts may be inexpensive sources of bioactive compounds. For example, mandarins (Citrus nobilis X Citrus deliciosa) are a potential source of flavonoid antioxidants. However, the metabolism of flavonoids in the gut limits their potential as nutritional supplements; colloidal delivery systems that protect flavonoids from metabolism may overcome this barrier. Here, we examined the flavonoid profile of mandarin peel. To this end, dried and pulverized peels were subjected to supercritical fluid extraction, and the extract contained 47.3±1.06 mg/ml rutin equivalents of total flavonoids. Mass spectral analysis revealed the predominance of polymethoxyflavones, chiefly tangeretin and nobiletin. We tested the pre-systemic metabolism of these flavonoids in an in vitro cell-free gastric environment and observed that nearly 50% of the flavonoids degraded within the first 2 hours of gastric exposure. To limit this, we nanoencapsulated flavonoids with polylactic-co-glycolic acid to a particle size of 200–250 nm. This monolayer nanoparticle system protected flavonoids in the gastric environment, allowing only 20% to be released in the first 2 h. To further protect the flavonoids, we constructed a bilayered delivery system by embedding the nanoencapsulated flavonoids in alginate hydrogels. This achieved 100% protection from pre-systemic release of flavonoids. Cryo-scanning electron microscopy showed that the nanoencapsulated flavonoids were well encapsulated in the dense pockets of alginate hydrogel. The monolayered and bilayered systems protected the flavonoids and either could be used for functional foods, depending upon the intended application and format (for example, as a liquid-flavonoid PLGA nanoparticles or a solid formulation- nanoparticle infused hydrogel). Kinetic modeling was studied in order to depict the mechanism of release behind the delivery vehicles and it was found that the Korsmeyer–Peppas model was the best fit for monolayered system and the Higuchi model as suitable fit for the bilayered system, the difference being in the mechanism of release i.e., Fickian diffusion for the monolayered system and Supercase II transport mechanism for bilayered system. This work underpins the role of carriers in the efficient delivery of flavonoids, in addition to the importance of extracting valuable bioactives from waste, thereby leading to sustainable valorization.
