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Tahiti lime is one of the most exported fruits in Brazil, and the state of São Paulo accounts for more than half of the country's fruit production, and drought in the region is a growing concern as rainfall distribution has become increasingly unpredictable. Therefore, identifying the best varieties and management strategies for citrus groves has become a subject of increasing research. This experiment was conducted at the "Sylvio Moreira" Citrus Center, Brazil; the experiment focused on different planting and mulching practices and scion-rootstock combinations. Two planting/management types were tested: (i) conventional tillage – CT (no mulch in the citrus row) and no-tillage – NT (mulch maintained in the citrus row), using Urochloa ruziziensis as an intercrop. Six grafts x rootstocks were tested: Tahiti acid IACC 5, IAC 10, and BRS IAC EECB Ponta Firme grafted onto two dwarf rootstocks: trifoliate orange IAC 718 Flying Dragon and citrandarin IAC 3152 Itajobi. Over three harvests (2022–2024), this study evaluated foliar nutrition, fruit quality, root development, water potential, gas exchange, water deficit biomarkers, and overall yield. No-tillage significantly improved vital performance indicators compared to conventional tillage. Plants managed with NT exhibited superior root development, greater water uptake, and greater leaf water potential. They also showed greater photosynthetic efficiency, leading to higher yields and improved fruit quality, particularly in juice yield and soluble solids/acidity ratio. The IAC 3152 Itajobi rootstock demonstrated remarkable resilience to drought stress, outperforming Flying Dragon in root development and physiological metrics. NT promoted healthier root systems and more robust plant growth. In contrast, conventional tillage led to poorer root growth, lower nutrient uptake, and increased disease susceptibility due to soil exposure and reduced water infiltration. Despite these challenges, 3,152 rootstock maintained active physiological responses such as gas exchange and/or water potential, especially with the Firm Tip graft. In conclusion, the integration of dwarf rootstocks with NT practices offers a viable strategy to increase the sustainability and productivity. This study highlights the importance of selecting appropriate scion-rootstock combinations and adopting sustainable management practices to improve resilience to environmental stress and optimize fruit yield and quality. [ABSTRACT FROM AUTHOR]

Because of the low fertility soils native to southeast Florida and the high nutrient demand of citrus trees under citrus greening-an endemic bacterial disease impacting nutrient uptake-growers are returning to the use of cover crops to improve soil fertility. Cover crops, specifically legumes, can improve soil nitrogen (N) availability because of their ability to fix N from the atmosphere. More citrus growers in southeast Florida are growing cover crops; however, there is a lack of recent research of suitable legume species and their impact on soil N cycling. To address this gap in the literature, six different treatments consisting of five legume species monocultures and one fallow plot (control) were organized into a completely randomized design. The experiment was conducted twice under warm and cool season conditions, and each treatment was replicated five times (n 5=5), for a total of 30 experimental plots. Legume species were hairy indigo (Indigofera hirsuta), sunn hemp (Crotalaria juncea), cowpea (Vigna unguiculata), alfalfa (Medicago sativa), and aeschynomene (Aeschynomene americana). Biomass production, N concentration, and nodule characteristics as well as their impact on soil N were measured over a 1-year span in both warm and cool seasons. Overall, both cowpea and hairy indigo produced more biomass and, as a result, higher tissue N compared with those of the other legumes at both 60 and 150 days after planting. However, no impact on soil N was observed. Additionally, all legumes were unable to survive in the cool season, resulting in no measurable biomass at 150 days after planting. These results are relevant for citrus growers aiming to enhance soil fertility through cover crops in southeast Florida. While several legume options are available for the warm season (e.g., cowpea, hairy indigo, and sunn hemp), suitable legume species for the cool season have yet to be identified. [ABSTRACT FROM AUTHOR]

Advance glycation end products (AGEs) are the main reason for diabetic complications. Persistent hyperglycemia and non‐enzymatic glycation increase the rate of AGEs formation. Natural functional food‐based approaches are mainly under investigation these days to discover new treatment options. We focused to investigate potential of medium polar fractions of Citrus paradesi. The peels fractions were analsyed for phytochemical profile, FTIR, HPLC‐DAD, and LCMS‐QTof, and biological investigation including antioxidant assays, α‐glucosidase inhibition, and Anti AGEs inhibition was performed. LCMS‐QTof confirmed the presence of flavonoids and polymethoxylated flavonoids including naringin, narirutin 4‐O‐glucoside, hesperidin, naringenin‐7‐O‐rutinoside hexamethoxyflavone, 3,5,6,7,8,3′,4′ heptamethoxyflavone were major compounds. A significant antioxidant activity was recorded in case of chloroform fraction compared to ethyl acetate fraction. Similarly a substancial AGEs inhibition in oxidative mode (IC50 0.23 mg/mL) and non‐oxidative mode (IC50 0.10 mg/mL) was observed in chloroform fraction, whereas ethyl acetate fraction was only active in oxidative mode (IC50 0.69 mg/mL). A moderate α‐glucosidase inhibition (IC50 1.23 mg/mL) was noticed in total extract, while significant activity was recorded in chloroform fraction (IC50 0.78 mg/mL). It was concluded that medium polar fraction of C. paradesi possesses antidiabetic and anti‐AGEs potential that can be due to presence of flavonoids and polymethoxylated flavonoids. [ABSTRACT FROM AUTHOR]

Tahiti lime is one of the most exported fruits in Brazil, and the state of São Paulo accounts for more than half of the country’s fruit production, and drought in the region is a growing concern as rainfall distribution has become increasingly unpredictable. Therefore, identifying the best varieties and management strategies for citrus groves has become a subject of increasing research. This experiment was conducted at the “Sylvio Moreira” Citrus Center, Brazil; the experiment focused on different planting and mulching practices and scion-rootstock combinations. Two planting/management types were tested: (i) conventional tillage – CT (no mulch in the citrus row) and no-tillage – NT (mulch maintained in the citrus row), using Urochloa ruziziensis as an intercrop. Six grafts x rootstocks were tested: Tahiti acid IACC 5, IAC 10, and BRS IAC EECB Ponta Firme grafted onto two dwarf rootstocks: trifoliate orange IAC 718 Flying Dragon and citrandarin IAC 3152 Itajobi. Over three harvests (2022–2024), this study evaluated foliar nutrition, fruit quality, root development, water potential, gas exchange, water deficit biomarkers, and overall yield. No-tillage significantly improved vital performance indicators compared to conventional tillage. Plants managed with NT exhibited superior root development, greater water uptake, and greater leaf water potential. They also showed greater photosynthetic efficiency, leading to higher yields and improved fruit quality, particularly in juice yield and soluble solids/acidity ratio. The IAC 3152 Itajobi rootstock demonstrated remarkable resilience to drought stress, outperforming Flying Dragon in root development and physiological metrics. NT promoted healthier root systems and more robust plant growth. In contrast, conventional tillage led to poorer root growth, lower nutrient uptake, and increased disease susceptibility due to soil exposure and reduced water infiltration. Despite these challenges, 3,152 rootstock maintained active physiological responses such as gas exchange and/or water potential, especially with the Firm Tip graft. In conclusion, the integration of dwarf rootstocks with NT practices offers a viable strategy to increase the sustainability and productivity. This study highlights the importance of selecting appropriate scion-rootstock combinations and adopting sustainable management practices to improve resilience to environmental stress and optimize fruit yield and quality.

Citrus spp. are recalcitrant to in vitro shoot regeneration and we report an improved in planta protocol for genetic transformation of rough lemon that bypasses shoot regeneration in tissue culture. The features of the protocol were the use of an Agrobacterium suspension with an OD600 nm = 0.6–1.0 supplemented with 100 μg acetosyringone, gentle shaking of embryo axes pricked at shoot apical meristems (from 2-day-old germinating seeds) at 70 rpm during agro-infection, followed by growth and development of plantlets at 30 °C. PCR screening of 2-month-old T0 plants revealed the presence of an amplicon corresponding to the β-1,3-glucanase gene in the primary branches of 25 plants with a transformation efficiency of 7.74%. PCR analysis of the secondary branches of these plants after 18 months showed chimerism, i.e., the coexistence of transformed and untransformed branches in all 25 plants. Quantification of β-1,3-glucanase expression in the transformed secondary branches by qRT-PCR showed that plant number 32 had maximum (3.71-fold) relative transgene expression. The qRT-PCR analysis of all four tertiary branches arising from the transformed secondary branch of plant number 32 showed no significant differences in expression among themselves and from the transformed secondary branch, suggesting restoration of the transformed branches with uniform expression and dissociation of chimerism. Scanning electron microscopy examination of leaves from secondary and tertiary branches that uniformly expressed the transgene showed a smooth, waxy surface with non-significant variation in stomata, which had a narrow opening and a mean pore length of 4.22 ± 0.25–5.09 ± 0.36 µm. In contrast, the leaves of untransformed branch had a rough surface and a significantly large stomatal opening with a mean pore length of 7.82 ± 0.67 µm. The micro-morphological characteristics of the leaves confirmed the dissociation of chimerism in the transformed tertiary branches of plant number 32. The study demonstrates identification of chimerism after in planta transformation using PCR technique, and the novelty relates to monitoring dissociation of chimerism in transformed tertiary branches of T0 generation using qRT-PCR analysis and its corroboration by electron microscopy. The protocol for genetic transformation in plants described in the present study can be used for trait improvement by transgenesis. [ABSTRACT FROM AUTHOR]

The dynamics and intensity of new shoot flushes of ‘Pera’ sweet orange scions [Citrus × sinensis (L.) Osbeck] grafted onto ‘Rough’ lemon (Citrus × limonia var. jambhiri Lush.), ‘Swingle’ citrumelo [Citrus × aurantium var. paradisi x Poncirus trifoliata (L.) Raf.] and ‘Sunki’ mandarin (Citrus reticulata ‘Sunki’) rootstocks were evaluated in the field at a citrus farm located in a northern region of the state of Sao Paulo, Brazil. Every 20 days for 16 months, new shoots were counted within a square frame of 0.25 m2 set on the central portion of the canopy and classified based on their phenological stages. Trees on ‘Swingle’ rootstock produced a lower area under the flush shoot dynamics curve (AUFSD) and mean number of new shoots than trees on ‘Rough’ lemon or ‘Sunki’ mandarin. For trees on all three rootstocks, new shoot intensities varied significantly over time with the greatest number of new shoots developing during late spring and early summer. Increases in minimum air temperature and available soil water were important indicators of overall emergence of new shoots.

Citrus represents one of the main fruit crops grown in the world, highlighting the 'Tahiti' acid lime tree. The objective was to compare rootstock varieties combined with this scion to identify those with the best agronomic performance and precocity of production, in addition to Phytophthora gummosis resistance. The experiment was carried out in Capitão Poço, northeast region of Pará, and the following seven rootstock genotypes were evaluated: 'Sunki Tropical', 'BRS O S Passos', 'BRS Bravo', 'BRS Donadio', 'Citrandarin Indio', 'BRS Matta', and 'LVK x LCR-038'. A randomized block experimental design was used, with three replications and 10 plants per plot. The evaluated characteristics were: plant height (m); crown volume (m³); number of ripe fruit per plant; total yield of ripened fruit per plant (kg plant-1); cumulative fruit yield (fruit kg plant-1); and average productive efficiency (fruit kg m-3 of crown). The average productive efficiency was high. For early selection, the best rootstocks in terms of yield, stability and adaptability were Sunki Tropical, BRS O S Passos, and Cintradarin Indio. The fruit number had the greatest direct effect on fruit yield, and crown pruning was directly harmful. Further studies to understand the complex interaction of G x E for BRS Donadio and Sunki Tropical should be carried out. [ABSTRACT FROM AUTHOR]

The citrus industry in Florida faces a destructive endemic disease, known as huanglongbing (HLB), associated with Candidatus Liberibacter asiaticus (CLas), a phloem-limited bacterium, and transmitted by the Asian citrus psyllid (ACP). Rootstocks are regarded as critical to keep citrus production commercially viable and help trees cope with the disease. Although most scions are susceptible, some rootstocks are HLB-tolerant and may influence ACP infestation and CLas colonization and therefore the grafted tree tolerance. This study aimed to elucidate the relative influence of rootstock and scion on insect vector infestation and CLas colonization under natural HLB-endemic conditions. Seven commercial rootstock cultivars with different genetic backgrounds were grafted with ‘Valencia’ sweet orange (Citrus sinensis) or were self-grafted (non-‘Valencia’) and planted in an open field where ACP and CLas were abundant. ACP infestation was determined weekly during periods of leaf flushing, and leaves and roots were analyzed every 3 months to determine CLas titers. Trees with ‘Valencia’ scion were more attractive to the psyllids than non-‘Valencia’ scions. This was also associated with a higher number of bacteria and a larger abundance of foliar HLB symptoms. The influence of the rootstock on the psyllid attraction of grafted ‘Valencia’ scion was less evident, and leaf CLas titers were similar regardless of the rootstock. Among the non-‘Valencia’ scions, Carrizo had the lowest and US-942 the highest leaf CLas titers. Root CLas titers also varied among cultivars, and standard sour orange roots harbored more bacteria than some trifoliate orange hybrid rootstocks such as US-942. In some trees, CLas was detected first in the roots 4 months after planting, but root CLas titers remained low throughout the study. In contrast, leaf CLas titers increased over time and were considerably higher than root titers from 7 months until the end of the study, 15 months after planting. Overall, the results of this study demonstrate a greater relative influence of the scion than the rootstock on ACP infestation and CLas colonization during the early stages of infection. This suggests that other cultivar-specific traits, such as the ability to tolerate other stresses and to absorb water and nutrients more efficiently, along with influences on the scion phenology, may play a larger role in the rootstock influence on the grafted tree tolerance during the later stages of HLB progression.

ABSTRACT The objective of this study was to evaluate the physico-chemical characteristics of fruits of 58 sweet orange tops cultivars on four rootstocks, namely: ‘Sunki Tropical’ mandarin and ‘Trifoliata’ Citrandarin ‘San Diego’, ‘Riverside’ and ‘Indio’. For this purpose, a completely randomized experimental design was used, in a factorial scheme (58 x 4). The characteristics analyzed were: equatorial diameter, fruit mass, peel thickness, number of seeds, soluble solids, titratable acidity, Ratio and juice yield. All the characteristics analyzed were influenced by both the tops cultivar and the rootstock, demonstrating that both factors interfere in the physicochemical quality of the fruits. The tops ‘Pera D-3’, ‘Pera Olimpia’, ‘Pera Bianchi’, ‘Jaffa’ and ‘Westin’ on all rootstocks evaluated showed characteristics in their fruits with soluble solids greater than 10 ºBrix, Ratio above 9.5 and juice yield greater than 45%, characteristics that define fruits with quality standards. Also, the tops ‘Pera Olimpia’, ‘Sincorá’ and ‘Westin’ on the rootstock ‘Sunki Tropical’, ‘Pera D-3’, ‘Pera D-25’, ‘Sincorá’, ‘Aquiri’ and ‘Russas P.S.’ on the rootstock ‘San Diego’, ‘Pera C-32’, ‘Pera D-3’, ‘Pera D-6’, ‘Pera E-6’, ‘Pera Bianchi’, ‘Pera CE-03 ‘, ‘Salustiana’ and ‘Westin’ on ‘Riverside’ rootstock are suitable for the juice production industry with Ratio between 14 and 16 and juice yield greater than 50%. It is also worth noting that the tops ‘Crescent’, ‘Natal Folha Murcha’, ‘Valencia Midknight’ and ‘Valencia Delta’ produced fruits without seeds on all rootstocks.

Obtaining citrus polyploids, especially from triploid individuals, is of great importance for genetic improvement programs, as they produce seedless fruits. Therefore, the aim of this study was to use flow cytometry analyses to identify polyploid individuals among tangerine-type seedlings originating from seeds germinated in vitro. Fruits were collected from 13 different genotypes in the municipality of Mucugê (state of Bahia, Brazil). The seeds were then removed and classified as developed (seeds with well-formed integument), underdeveloped (seeds with wrinkled integument) and small (seeds of 1/3 to 1/6 of normal size). After the integument was removed, the seeds were disinfected and introduced into a WPM culture medium, in which they remained for 120 days. After this period, the percentage of germinated seeds and growth variables were evaluated, and ploidy analysis was conducted using flow cytometry. The developed seeds displayed a higher germination rate (91.5%) than the others. The small and underdeveloped seeds resulted in a considerable frequency of spontaneous polyploids (11%), and one haploid plant was also obtained from the latter class. Key message: The ploidy of 13 citrus genotypes was investigated using flow cytometry. In addition to polyploid plants that are of interest to breeding programs, there was the identification of a haploid plant. [ABSTRACT FROM AUTHOR]

Citrus scion/rootstock combinations alter the concentration of bioactive compounds in orange juice. The shelf life of freshly squeezed juice can be maximized through packaging and storage. The profiles of ascorbic (AA), dehydroascorbic acid (DHAA), and phenolic compounds were analyzed in juices of four sweet orange scions, Sanguínea de Mombuca (SM), Rubi (R), Lue Gin Gong (LGG), and Valência Delta Seedless (VDS), grafted onto 'Rangpur' lime (RL) and 'Swingle' citrumelo (SC) rootstocks. The juices obtained from the combination of the 'Rubi' orange in both rootstocks stood out by their higher concentration of ascorbic acid (AA) and dehydroascorbic acid (DHAA). Overall, all SC-grafted scions showed higher AA and DHAA and some phenolic compound concentrations. In all combinations, phenolic compounds showed the highest concentrations in the juices at the time of fruit extraction and decreased during storage. Dark packaging provided higher bioactive compounds in juices stored for longer periods. These findings can contribute to the diversification of scion/rootstock cultivars in order to increase the variety of orchards by choosing the best combinations for pasteurized orange juice with higher nutritional value. [ABSTRACT FROM AUTHOR]

Citrus (Citrus spp. L.), which has high nutritional and economic value, is one of the most commonly grown fruits in Turkey. In spring 2020, large aerial galls (tumors) were observed on trunks and main branches of mandarin (Citrus reticulata cv. Satsuma) and lemon (Citrus limon cv. Kutdiken) trees grafted to sour orange (Citrus aurantium L.) in commercial citrus orchards in Hatay and Mersin provinces of Turkey. Disease incidence was 0.2–1.0% in the orchards inspected. Six bacterial isolates were obtained from young tumors on King's B (KB) medium. Several biochemical and morphological characteristics of all isolates were consistent with the description of the tumorigenic bacterium Agrobacterium tumefaciens (= Agrobacterium biovar 1). Identification of these isolates was confirmed by comparison with reference isolates of Agrobacterium tumefaciens (Syn. Rhizobium radiobacter) using MALDI-TOF MS analysis. The pathogenicity of the isolates was confirmed on carrot slice and stems from 6-month-old Kalanchoe plants and 2-year-old mandarin (cv. Satsuma) saplings. For molecular identification, the 16S rRNA and virD2 genes were amplified with primer pairs 27F/1492R and VirD2A/VirD2C, respectively and the PCR products were sequenced for representative isolates (CAt21, CAt27). The partial sequences of 16S rRNA (accessions numbers MZ708735 and MZ708734) and VirD2A/VirD2C of the representative isolates (CAt21, CAt27) showed 100% nucleotide identity to the A. tumefaciens isolates available in GenBank. According to symptoms, biochemical characteristics, pathogenicity test and molecular analyses, the causative agent of the disease was identified as Agrobacterium tumefaciens (= Agrobacterium biovar 1). To our knowledge, this is the first report of Agrobacterium tumefaciens (= Agrobacterium biovar 1) on citrus in Turkey. [ABSTRACT FROM AUTHOR]

The essential oil derived from Citrus plants has long been used for medicinal purposes, due to its broad spectrum of therapeutic characteristics. To date, approximately 162 Citrus species have been identified, and many investigational studies have been conducted to explore the pharmacological potential of Citrus spp. oils. This study investigated the volatile constituents of essential oil distilled from the leaves of C. hystrix, C. limon, C. pyriformis, and C. microcarpa, using gas chromatography–quadrupole mass spectrometry. A total of 80 secondary compounds were tentatively identified, representing 84.88–97.99% of the total ion count and mainly comprising monoterpene (5.20–76.15%) and sesquiterpene (1.36–27.14%) hydrocarbons, oxygenated monoterpenes (3.91–89.52%) and sesquiterpenes (0.21–38.87%), and other minor chemical classes (0.10–0.52%). In particular, 27 compounds (1.19–39.06%) were detected across all Citrus species. Principal component analysis of the identified phytoconstituents and their relative quantities enabled differentiation of the Citrus leaf oils according to their species, with the loading variables contributing to these metabolic differences being identified. The Citrus leaf oils were tested for their antioxidant and antiproliferative activities using 2,2-diphenyl-1-picryl-hydrazylhydrate (DPPH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. The results indicated that C. limon displayed the highest DPPH radical scavenging ability (IC50 value of 29.14 ± 1.97 mg/mL), while C. hystrix exhibited the lowest activity (IC50 value of 279.03 ± 10.37 mg/mL). On the other hand, all the Citrus oils exhibit potent antiproliferative activities against the HeLa cervical cancer cell line, with IC50 values of 11.66 μg/mL (C. limon), 20.41 μg/mL (C. microcarpa), 25.91 μg/mL (C. hystrix), and 87.17 μg/mL (C. pyriformis). [ABSTRACT FROM AUTHOR]

The establishment of minimum growth conditions is essential for in vitro germplasm conservation. Changes to the basic medium and carbon source concentrations are important factors for reducing plant growth in vitro. This study adjusted a protocol for the in vitro conservation of 'Florida Rough' lemon plants. Microcuttings (approximately 1 cm) from plants that were previously cultivated in vitro were inoculated into test tubes with 10 mL of woody plant medium (WPM) at different concentrations (1/1, 1/2 and 1/4) and supplemented with 0, 12.5, 25 and 50 g.L-1 of sucrose, solidified with 7 g.L-1 agar and adjusted to pH 5.8. The experiment was completely randomized in a 3 x 4 factorial design with 15 replications and was maintained under controlled conditions for 360 days. After this period the plant height in cm (PH), the plant dry mass in g (PDM) and the 21 numbers of green leaves (NGL), senescent leaves (NSL) and microcuttings (NM) were evaluated. The variables that best explained the observed behavior of the 'Florida Rough' lemon plants were NGL and PH, with values of 61.63 and 35.08%, respectively. The original concentration of the WPM with the addition of 25 g. L-1 of sucrose yielded the best 'Florida Rough' lemon plant growth reduction in vitro while maintaining the physiologically health of the plants. [ABSTRACT FROM AUTHOR]

Due to their special peel tissue, comprising a dense flavedo (exocarp), a less dense albedo (mesocarp), and a thin endocarp, most citrus fruits can withstand the drop from a tree or high shrub (relatively) undamaged. While most citrus fruit peels share this basic morphological setup, they differ in various structural and mechanical properties. This study analyzes how various properties in citrus peels of the pomelo, citron, lemon, grapefruit, and orange affect their compression behavior. We compare the structural and biomechanical properties (e.g., density, stress, Young’s modulus, Poisson’s ratio) of these peels and analyze which properties they share. Therefore, the peels were quasi-statically compressed to 50% compression and analyzed with manual and digital image correlation methods. Furthermore, local deformations were visualized, illustrating the inhomogeneous local strain patterns of the peels. The lateral strain of the peels was characterized by strain ratios and the Poisson’s ratio, which were close to zero or slightly negative for nearly all tested peels. Our findings prove that—despite significant differences in stress, magnitude, distribution, and thickness - the tested peels share a low Poisson’s ratio meaning that the general peel structures of citrus species offer a promising inspiration for the development of energy dissipating cellular structure that can be used for damage protection.

Para obter uma citricultura competitiva é necessário que o agricultor disponha de variedades que atendam a diversos requisitos, tais como: boa produção, frutos de qualidade e oferta em períodos de entressafra dos principais genótipos cultivados. Portanto, o objetivo deste trabalho foi avaliar o desempenho agronômico de cultivares cítricos do grupo das laranjeiras e tangerineiras em pomar implantado no município de Biguaçu, Grande Florianópolis, no ano de 2010. Foram estudados parâmetros referentes ao crescimento vegetativo, eficiência produtiva, morfologia dos frutos e características de qualidade interna dos frutos. Os cultivares cítricos apresentaram qualidade compatível com a demanda do mercado de frutas de mesa e também apresentaram bom desempenho agronômico com destaque para ‘Champanha’ e ‘Satsuma Okitsu’.

The narrow genetic pool for both scions and rootstocks used in the Brazilian orchards makes the citrus industry vulnerable to biotic and abiotic threats. Orchard diversification by using different scion–rootstock combinations is an efficient measure to promote citrus protection, through increasing the level of genetic diversity. In this paper, we report the horticultural performance of the mid-season 'Shamouti' sweet orange grafted on five different rootstocks ('Rangpur' lime, 'Swingle' citrumelo, 'C-13′ citrange, and 'Cleopatra' and 'Sunki' mandarins) in a long-term experiment (2007–2017) under the Brazilian humid subtropical condition. 'Shamouti' trees were assessed for vegetative growth, yield, and fruit quality. Additionally, a study was performed to estimate tree density and yield for new plantings. Trees grafted on 'Swingle' and 'C-13′ rootstocks were less vigorous and more productive, with cumulative yields of >480 kg per tree, allowing high-density plantings (363–337 trees·ha−1). Trees on 'Cleopatra', 'Sunki', and 'Rangpur' were the most vigorous among the tested rootstocks, with tree heights > 4.20 m. However, they took longer to establish in the field, evidenced by their growth progress. These combinations also displayed the lowest tree density estimation (≤311 trees·ha−1). Trees on 'Cleopatra' exhibited the lowest cumulative yield (255 kg per tree). Although some significant differences were found for fruit quality, all rootstock combinations produced fruit of suitable quality, attending the commercial grading. Our findings evidence the potential of the trifoliate orange-related rootstocks 'C-13′ and 'Swingle' to be used as promising rootstocks for 'Shamouti' cultivation in the humid subtropics, promoting genetic diversification and enhancing yield and tree density in new orchards. [ABSTRACT FROM AUTHOR]

The citrus yield is limited by soil and/or water salinity, but appropriate rootstocks can ensure the sustainability of the production system. Therefore, the objective of the present research was to evaluate the salt content in the soil and the production and physiological aspects of the 'Tahiti' acid lime combined with thirteen rootstocks, irrigated with saline water in the first two production years to identify indicators of salt tolerance. The rootstocks evaluated were: 'Santa Cruz Rangpur' lime, 'Indio', 'Riverside' and 'San Diego' citrandarins, 'Sunki Tropical' mandarin, and eight hybrids, obtained from the Citrus Breeding Program of Embrapa Cassava and Fruits. The waters used had three saline levels: 0.14, 2.40, and 4.80 dS m−1, in a randomized block adopting a split-plot design, with rootstocks in the plots and saline waters in the subplots, with four replicates. From August 2019 to February 2021, fruit harvests and agronomic traits were measured. At the end of each production year, the soil characteristics, leaf gas exchange, and chlorophyll a fluorescence analysis were performed. It was concluded that: (1) the effects of water salinity on citrus are of osmotic nature, reducing gas exchange, (2) the salinity did not significantly damage the photosynthetic apparatus until the second year of production, and (3) using more stable, salt-tolerant rootstocks makes it possible to cultivate 'Tahiti' acid lime under irrigation with waters of 2.4 dS m−1 electrical conductivity. [ABSTRACT FROM AUTHOR]

Citrus black spot (CBS) symptom expression on sweet oranges has been reported to be affected by the fruit developmental stage and inoculum concentration in greenhouse conditions. However, there is little information concerning the period in which the fruit is susceptible in commercial orchards. This study assessed the influence of fruit age and inoculum concentration of Phyllosticta citricarpa on CBS intensity and fruit drop in the field. Two field trials were conducted in commercial 'Valencia' orchards in São Paulo state, Brazil. Fruit were inoculated from October (petal fall stage) to July (c.6.5 cm diameter), with 101, 103 and 105 pycnidiospores/ml. CBS symptoms and fruit drop were observed in higher levels for fruit inoculated from October to February than from March to July. In both trials, when fruit were inoculated 10 times from October to July or single‐inoculated in November or December, high CBS severities of 11%–22% were observed and the proportion of fruit remaining on the tree was 48%–77%; in contrast, noninoculated fruit had severity below 1.1% and 90% remained on the tree. Inoculations in November or December of green fruit with 1.5–3.0 cm diameter using 105 pycnidiospores/ml were associated with higher CBS intensity and fruit drop and shorter incubation period than inoculations with lower concentrations. This work provides a better understanding of fruit stages and P. citricarpa inoculum concentrations most related to symptom expression and losses under natural conditions and may be helpful for improvement of CBS management in the São Paulo citrus belt. [ABSTRACT FROM AUTHOR]

Citrus plants are grown in diverse regions of the world, from subtropical to semi-arid and humid tropical areas. Through mechanisms essential for their survival, they adapt to the environmental conditions to which they are subjected. Although there is vast literature on adaptation of citrus plants to individual stresses, plant responses to interaction among different types of stresses have not been clearly examined. Abiotic or biotic stresses, or a combination of these stresses, result in reorganization of plant energy resources for defense, whether it be for resistance, tolerance, or prevention of stress. Plants generally respond to these stress factors through production of secondary metabolites, such as volatile compounds, derived from different biosynthesis and degradation pathways, which are released through distinct routes. Volatile compounds vary among plant species, meeting the specific needs of the plant. Simultaneous exposure to the stress factors of water deficit and herbivory leads to responses such as qualitative and quantitative changes in the emission of secondary metabolites, and compounds may accumulate within the leaves or predispose the plant to more quickly respond to the stress brought about by the herbivore. The genetic makeup of citrus plants can contribute to a better response to stress factors; however, studies on the emission of volatile compounds in different citrus genotypes under simultaneous stresses are limited. This review examines the effects of abiotic stress due to water deficit and biotic stress due to herbivory by Diaphorina citri in citrus plants and examines their connection with volatile compounds. A summary is made of advances in knowledge regarding the performance of volatile compounds in plant defense against both stress factors, as well as the interaction between them and possible findings in citrus plants. In addition, throughout this review, we focus on how genetic variation of the citrus species is correlated with production of volatile compounds to improve stress tolerance. • To survive, citrus plants have evolved to cope with biotic and abiotic stresses. • Defense mechanisms include the production of secondary metabolites, such as volatile organic compounds. • Plant responses can be enhanced through the interaction between herbivory by D. citri and water deficit. • There is limited knowledge regarding plant responses to multiple stress factors such as water deficit and ACP herbivory. • Developing resilient cultivars that can withstand multiple stress factors is crucial in the face of climate change and HLB. [ABSTRACT FROM AUTHOR]

Citrus scion/rootstock combinations alter the concentration of bioactive compounds in orange juice. The shelf life of freshly squeezed juice can be maximized through packaging and storage. The profiles of ascorbic (AA), dehydroascorbic acid (DHAA), and phenolic compounds were analyzed in juices of four sweet orange scions, Sanguínea de Mombuca (SM), Rubi (R), Lue Gin Gong (LGG), and Valência Delta Seedless (VDS), grafted onto ‘Rangpur’ lime (RL) and ‘Swingle’ citrumelo (SC) rootstocks. The juices obtained from the combination of the ‘Rubi’ orange in both rootstocks stood out by their higher concentration of ascorbic acid (AA) and dehydroascorbic acid (DHAA). Overall, all SC-grafted scions showed higher AA and DHAA and some phenolic compound concentrations. In all combinations, phenolic compounds showed the highest concentrations in the juices at the time of fruit extraction and decreased during storage. Dark packaging provided higher bioactive compounds in juices stored for longer periods. These findings can contribute to the diversification of scion/rootstock cultivars in order to increase the variety of orchards by choosing the best combinations for pasteurized orange juice with higher nutritional value.

Diversification of rootstock varieties, with consequent reduction in phytosanitary risks, has great importance to the sustainability of citrus cultivation in the south of Brazil. This study evaluated the performance of 42 rootstocks in the nursery phase to generate 'Valencia Late' sweet orange seedlings. Therefore, nucellar seedlings from the rootstocks under study were analyzed in relation to plant height, stem diameter, mortality rate and percentage of bud set after grafting. The experimental design was completely randomized with four replications of 20 sample units. Not adapted genotypes had high mortality rates, and the ones of both hybrids LCR x CTSW - 009 and LVK x LCR - 038 were 100% and 90%, respectively. Other 13 genotypes had mortality rates above 30%, and 'Sunki' mandarin was the female genitor of ten of them. 'Swingle' citrumelo was the rootstock with the highest development (plant height and stem diameter), associated with low mortality rate. In relation to the other rootstocks, the best results were the fast grafting diameter, associated with low mortality rate obtained by hybrids HTR - 053, LRF x (LCR x TR) - 005, CLEO x TRBN - 245, CLEO x TRSW - 287, and citrandarins 'Indio', 'Riverside' and 'San Diego', as well as Trifoliate orange and 'Rangpur' lime. In addition to Trifoliate orange, which is widely used in Rio Grande do Sul, these rootstocks have great potential in citriculture in the south of Brazil. [ABSTRACT FROM AUTHOR]

Summary: 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. [ABSTRACT FROM AUTHOR]

Rootstocks modulate several characteristics of citrus trees, including vegetative growth, fruit yield and quality, and resistance or tolerance to pests, diseases, soil drought, and salinity, among other factors. There is a shortage of scion and rootstock cultivars among the combinations planted in Brazil. "Ponkan" mandarin and "Murcott" tangor grafted on "Rangpur" lime comprise the majority of the commercial mandarin orchards in Brazil. This low genetic diversity of citrus orchards can favor pest and disease outbreaks. This study aimed to evaluate the agronomic performance, Huanglongbing (HLB) tolerance, and fruit quality of "Emperor" mandarin on five different rootstocks for nine cropping seasons under the subtropical soil-climate conditions of the North region of the state of Paraná, Brazil. The experimental design was a randomized block, with six replications, two trees per block, and five rootstocks, including "Rangpur" lime, "Cleopatra," and "Sunki" mandarins, "Swingle" citrumelo, and "Fepagro C-13" citrange. The evaluations included tree growth, yield performance, fruit quality, and HLB disease incidence. "Emperor" mandarin trees grafted on "Rangpur" lime and "Swingle" citrumelo had early fruiting and high yield efficiency. "Rangpur" lime also induced the lowest tree growth, but low fruit quality. Trees on "Swingle" citrumelo and "Fepagro C-13" citrange showed low scion and rootstock affinity and produced fruits with high total soluble solids (TSS), with a lower number of seeds for those from trees on "Fepagro C-13" citrange. "Cleopatra" and "Sunki" mandarins induced higher juice content, while fruits from trees on "Cleopatra" also had higher TSS/titratable acidity (TA) ratio. "Emperor" mandarin trees were susceptible to HLB regardless of the rootstocks. Overall, "Cleopatra" and "Sunki" mandarins, "Swingle" citrumelo, and "Fepagro C-13" are more suitable rootstocks for "Emperor" mandarin under Brazilian subtropical conditions than "Rangpur" lime. [ABSTRACT FROM AUTHOR]

Rootstocks modulate several characteristics of citrus trees, including vegetative growth, fruit yield and quality, and resistance or tolerance to pests, diseases, soil drought, and salinity, among other factors. There is a shortage of scion and rootstock cultivars among the combinations planted in Brazil. “Ponkan” mandarin and “Murcott” tangor grafted on “Rangpur” lime comprise the majority of the commercial mandarin orchards in Brazil. This low genetic diversity of citrus orchards can favor pest and disease outbreaks. This study aimed to evaluate the agronomic performance, Huanglongbing (HLB) tolerance, and fruit quality of “Emperor” mandarin on five different rootstocks for nine cropping seasons under the subtropical soil-climate conditions of the North region of the state of Paraná, Brazil. The experimental design was a randomized block, with six replications, two trees per block, and five rootstocks, including “Rangpur” lime, “Cleopatra,” and “Sunki” mandarins, “Swingle” citrumelo, and “Fepagro C-13” citrange. The evaluations included tree growth, yield performance, fruit quality, and HLB disease incidence. “Emperor” mandarin trees grafted on “Rangpur” lime and “Swingle” citrumelo had early fruiting and high yield efficiency. “Rangpur” lime also induced the lowest tree growth, but low fruit quality. Trees on “Swingle” citrumelo and “Fepagro C-13” citrange showed low scion and rootstock affinity and produced fruits with high total soluble solids (TSS), with a lower number of seeds for those from trees on “Fepagro C-13” citrange. “Cleopatra” and “Sunki” mandarins induced higher juice content, while fruits from trees on “Cleopatra” also had higher TSS/titratable acidity (TA) ratio. “Emperor” mandarin trees were susceptible to HLB regardless of the rootstocks. Overall, “Cleopatra” and “Sunki” mandarins, “Swingle” citrumelo, and “Fepagro C-13” are more suitable rootstocks for “Emperor” mandarin under Brazilian subtropical conditions than “Rangpur” lime.

The essential oil derived from Citrus plants has long been used for medicinal purposes, due to its broad spectrum of therapeutic characteristics. To date, approximately 162 Citrus species have been identified, and many investigational studies have been conducted to explore the pharmacological potential of Citrus spp. oils. This study investigated the volatile constituents of essential oil distilled from the leaves of C. hystrix, C. limon, C. pyriformis, and C. microcarpa, using gas chromatography–quadrupole mass spectrometry. A total of 80 secondary compounds were tentatively identified, representing 84.88–97.99% of the total ion count and mainly comprising monoterpene (5.20–76.15%) and sesquiterpene (1.36–27.14%) hydrocarbons, oxygenated monoterpenes (3.91–89.52%) and sesquiterpenes (0.21–38.87%), and other minor chemical classes (0.10–0.52%). In particular, 27 compounds (1.19–39.06%) were detected across all Citrus species. Principal component analysis of the identified phytoconstituents and their relative quantities enabled differentiation of the Citrus leaf oils according to their species, with the loading variables contributing to these metabolic differences being identified. The Citrus leaf oils were tested for their antioxidant and antiproliferative activities using 2,2-diphenyl-1-picryl-hydrazylhydrate (DPPH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. The results indicated that C. limon displayed the highest DPPH radical scavenging ability (IC50 value of 29.14 ± 1.97 mg/mL), while C. hystrix exhibited the lowest activity (IC50 value of 279.03 ± 10.37 mg/mL). On the other hand, all the Citrus oils exhibit potent antiproliferative activities against the HeLa cervical cancer cell line, with IC50 values of 11.66 μg/mL (C. limon), 20.41 μg/mL (C. microcarpa), 25.91 μg/mL (C. hystrix), and 87.17 μg/mL (C. pyriformis).

A fast, sensitive, accurate and robust GC-FID and confirmatory GC-MS method, was developed to simultaneously determine squalene and underivatized free plant sterols in Citrus essential oils (cEOs). The method was applied to assess the content of squalene and free plant sterols in four most commonly employed cold-pressed cEOs (bergamot, lemon, mandarin and orange). cEOs plant sterols exhibited distinctive molecular patterns, with levels ranging from 182 to 1100 mg kg−1 in lemon and bergamot essential oils, respectively. β-sitosterol was the dominant compound in all cases, with an average content of ∼650 mg kg−1 in bergamot and orange essential oils. Campesterol and brassicasterol occurred at much lower amount in all samples. Bergamot essential oil was also the richest in squalene (537 mg kg−1) compared to the other cEOs. The method developed could contribute to define compositional patterns of cEOs, thus supporting their versatile utilisation in the food and flavour industry. [ABSTRACT FROM AUTHOR]

The industrial production of citrus plants for ornamental use (ornacitrus) began in Italy at the end of the 1960s due to the need for many citrus nurseries to adapt their activities in a time of crisis for citriculture. Nowadays, the ornamental citrus nursery sector is a well-established industry in many European countries such as Portugal, Spain, Greece, and southern Italy. In Italy, nursery production of ornamental citrus plants has become prominent due to the gradual shutdown of many commercial citrus orchards. Currently, Italy maintains its leadership with more than 5.5 million ornacitrus plants produced annually. Ornamental citrus production regards mainly different cultivars of Citrus and Fortunella species, with lemon as the lead species. In this paper, the contribution of breeding and cultural techniques to the innovation of the sector is reported and discussed. This review aims to give an updated scientific and technical description of a sector with large competitive potential that remains still largely unexplored, pointing out its strengths and weaknesses.

The citrus yield is limited by soil and/or water salinity, but appropriate rootstocks can ensure the sustainability of the production system. Therefore, the objective of the present research was to evaluate the salt content in the soil and the production and physiological aspects of the ‘Tahiti’ acid lime combined with thirteen rootstocks, irrigated with saline water in the first two production years to identify indicators of salt tolerance. The rootstocks evaluated were: ‘Santa Cruz Rangpur’ lime, ‘Indio’, ‘Riverside’ and ‘San Diego’ citrandarins, ‘Sunki Tropical’ mandarin, and eight hybrids, obtained from the Citrus Breeding Program of Embrapa Cassava and Fruits. The waters used had three saline levels: 0.14, 2.40, and 4.80 dS m−1, in a randomized block adopting a split-plot design, with rootstocks in the plots and saline waters in the subplots, with four replicates. From August 2019 to February 2021, fruit harvests and agronomic traits were measured. At the end of each production year, the soil characteristics, leaf gas exchange, and chlorophyll a fluorescence analysis were performed. It was concluded that: (1) the effects of water salinity on citrus are of osmotic nature, reducing gas exchange, (2) the salinity did not significantly damage the photosynthetic apparatus until the second year of production, and (3) using more stable, salt-tolerant rootstocks makes it possible to cultivate ‘Tahiti’ acid lime under irrigation with waters of 2.4 dS m−1 electrical conductivity.

The narrow genetic pool for both scions and rootstocks used in the Brazilian orchards makes the citrus industry vulnerable to biotic and abiotic threats. Orchard diversification by using different scion–rootstock combinations is an efficient measure to promote citrus protection, through increasing the level of genetic diversity. In this paper, we report the horticultural performance of the mid-season ‘Shamouti’ sweet orange grafted on five different rootstocks (‘Rangpur’ lime, ‘Swingle’ citrumelo, ‘C-13′ citrange, and ‘Cleopatra’ and ‘Sunki’ mandarins) in a long-term experiment (2007–2017) under the Brazilian humid subtropical condition. ‘Shamouti’ trees were assessed for vegetative growth, yield, and fruit quality. Additionally, a study was performed to estimate tree density and yield for new plantings. Trees grafted on ‘Swingle’ and ‘C-13′ rootstocks were less vigorous and more productive, with cumulative yields of >480 kg per tree, allowing high-density plantings (363–337 trees·ha−1). Trees on ‘Cleopatra’, ‘Sunki’, and ‘Rangpur’ were the most vigorous among the tested rootstocks, with tree heights > 4.20 m. However, they took longer to establish in the field, evidenced by their growth progress. These combinations also displayed the lowest tree density estimation (≤311 trees·ha−1). Trees on ‘Cleopatra’ exhibited the lowest cumulative yield (255 kg per tree). Although some significant differences were found for fruit quality, all rootstock combinations produced fruit of suitable quality, attending the commercial grading. Our findings evidence the potential of the trifoliate orange-related rootstocks ‘C-13′ and ‘Swingle’ to be used as promising rootstocks for ‘Shamouti’ cultivation in the humid subtropics, promoting genetic diversification and enhancing yield and tree density in new orchards.

Huanglongbing is a highly destructive citrus disease associated with “Candidatus Liberibacter asiaticus” (Las), a phloem−limited and non-culturable bacterium, naturally transmitted by the psyllid Diaphorina citri. Although diverse approaches have been used to understand the molecular mechanisms involved in the pathogen–host interaction, such approaches have focused on already infected and/or symptomatic plants, missing early events in the initial days post-inoculation. This study aimed to identify the time course of Las multiplication and whole-plant colonization immediately following inoculation by infected psyllids feeding for 2 days. Thus, the experimental approach was to track Las titers after psyllid inoculation in new shoots (NS) of Citrus × sinensis (susceptible), Murraya paniculata (partially resistant), and Bergera koenigii (fully resistant). Soon after psyllid removal, Las titers dropped until the 10–12th days in all three species. Following this, Las titers increased exponentially only in C. × sinensis and M. paniculata, indicating active bacterial multiplication. In C. × sinensis, Las reached a stationary phase at ∼5 log Las cells/g of tissue from the 40th day onward, while in M. paniculata, Las increased at a lower rate of up to ∼3 log Las cells/g of tissue between the 40th and 60th days, decreasing gradually thereafter and becoming undetectable from the 160th day onward. In B. koenigii, Las titers decreased from the start and remained undetectable. In C. × sinensis, an average of 2.6 log of Las cells/g of tissue was necessary for Las to move out of 50% of the NS in 23.6 days and to colonize the rest of the plant, causing a successful infection. Conversely, the probability of Las moving out of the NS remained below 50% in M. paniculata and zero in B. koenigii. To our knowledge, this is the first study on Las dynamics and whole-plant colonization during the earliest stages of infection. Identification of critical time-points for either successful multiplication or Las resistance may help to elucidate initial events of Las–host interactions that may be missed due to longer sampling intervals and at later stages of infection.

Huanglongbing is a highly destructive citrus disease associated with " Candidatus Liberibacter asiaticus" (Las), a phloem−limited and non-culturable bacterium, naturally transmitted by the psyllid Diaphorina citri. Although diverse approaches have been used to understand the molecular mechanisms involved in the pathogen–host interaction, such approaches have focused on already infected and/or symptomatic plants, missing early events in the initial days post-inoculation. This study aimed to identify the time course of Las multiplication and whole-plant colonization immediately following inoculation by infected psyllids feeding for 2 days. Thus, the experimental approach was to track Las titers after psyllid inoculation in new shoots (NS) of Citrus × sinensis (susceptible), Murraya paniculata (partially resistant), and Bergera koenigii (fully resistant). Soon after psyllid removal, Las titers dropped until the 10–12th days in all three species. Following this, Las titers increased exponentially only in C. × sinensis and M. paniculata , indicating active bacterial multiplication. In C. × sinensis , Las reached a stationary phase at ∼5 log Las cells/g of tissue from the 40th day onward, while in M. paniculata , Las increased at a lower rate of up to ∼3 log Las cells/g of tissue between the 40th and 60th days, decreasing gradually thereafter and becoming undetectable from the 160th day onward. In B. koenigii , Las titers decreased from the start and remained undetectable. In C. × sinensis , an average of 2.6 log of Las cells/g of tissue was necessary for Las to move out of 50% of the NS in 23.6 days and to colonize the rest of the plant, causing a successful infection. Conversely, the probability of Las moving out of the NS remained below 50% in M. paniculata and zero in B. koenigii. To our knowledge, this is the first study on Las dynamics and whole-plant colonization during the earliest stages of infection. Identification of critical time-points for either successful multiplication or Las resistance may help to elucidate initial events of Las–host interactions that may be missed due to longer sampling intervals and at later stages of infection. [ABSTRACT FROM AUTHOR]

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Citrus post-bloom fruit drop (PFD) is caused by Colletotrichum acutatum and C. gloeosporioides species complexes and frequently occurs in São Paulo (SP) state, Brazil. The environmental requirements for conidial germination and appressorium formation have been already determined in vitro; however, the environmental conditions for infection in citrus flowers remain unknown. C. acutatum is considered the main species complex causing PFD in citrus, but a survey of the pathogen's prevalence has never been performed in SP state. The aims of this study were to assess the influence of different temperatures and wetness periods on infection of flowers by C. acutatum and C. gloeosporioides in potted citrus trees, and to determine the prevalence of both pathogens in different SP regions and sweet orange varieties. Environmental requirement trials were conducted in 2- to 3-year-old potted sweet orange trees. Flowers at different development stages (R2, R4 and R5) were inoculated with C. acutatum and C. gloeosporioides, and the trees were incubated at 18 or 24 °C for wetness periods of 6, 8, 12, 16 or 24 h. The percentages of inoculated flowers with PFD lesions and persistent calyces were calculated. The prevalence of both pathogens in SP regions was assessed in samples of diseased flowers collected at 16 commercial orchards of 'Natal', 'Valencia' and 'Pera' sweet oranges. The species complex was confirmed by isolation and PCR with species complex-specific primers. Blossom blight and persistent calyx incidences were higher in flowers inoculated with C. acutatum than in those inoculated with C. gloeosporioides. Incubation periods ranged from 2 to 5 days, and from 5 to 6 days for C. acutatum and C. gloeosporioides, respectively. In SP, irrespective of the region and sweet orange variety, C. acutatum was isolated from more than 80% of symptomatic flowers. We concluded that C. acutatum is not only more aggressive than C. gloeosporioides for causing PFD but also more prevalent in SP orchards. [ABSTRACT FROM AUTHOR]

Abstract The EFSA Panel on Plant Health performed a pest categorisation of Diaphorina citri (Hemiptera: Liviidae) (Asian citrus psyllid) for the EU. D. citri is a key pest of citrus in several countries as it is a vector of serious bacterial pathogens, the putative causal agents of Huanglongbing (HLB) also known as citrus greening. Eggs are laid on tips of growing shoots on and between unfurling leaves. Females may lay more than 800 eggs during their lives. Nymphs pass through five instars. The life cycle requires from 14 to 49 days, depending upon the season. There is no diapause, but populations are low in winter. It overwinters as an adult which may live for several months. The species completes 9–10 generations/year; however, under protected conditions, up to 16 generations have been recorded. Commission Implementing Regulation (EU) 2019/2072 (Annex IIA) regulates D. citri, as a quarantine pest not known to occur in the EU territory. Fruits and plants for planting provide potential pathways for entry into the EU. Climatic conditions and the availability of host plants provide conditions to support establishment in the EU. The introduction of D. citri would have an economic impact in the EU through direct but mainly indirect effects due to potential transmission of HLB. Phytosanitary measures are available to reduce the likelihood of entry. D. citri satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. D. citri does not meet the criteria of occurring in the EU, nor plants for planting being the principal means of spread, for it to be regarded as a potential Union regulated non‐quarantine pest.

Arid and semiarid regions are vulnerable to water deficits and salinity. Citrus plants are sensitive to saline stress and require the use of tolerant scion-rootstock combinations. Thus, this study aimed to evaluate and classify citrus scion-rootstock combinations with respect to their tolerance to salinity during seedling formation in a protected environment. An experiment was conducted in a randomized block design with a 5 x 12 x 2 factorial scheme corresponding to five levels of water salinity (0.8, 1.6, 2.4, 3.2, and 4.0 dS m-1) applied in 12 citrus rootstocks grafted with two scion varieties: ‘Tahiti’ acid lime and ‘Star Ruby’ grapefruit. The scion-rootstock combinations were evaluated for accumulated dry matter and survival index at 330 days after sowing the rootstocks. Salinity exerted different effects on the dry matter formation of scion-rootstock combinations. ‘Star Ruby’ was less sensitive to salinity, particularly when the rootstocks were the hybrids from ‘Sunki of Florida’ mandarin (TSKFL) with ‘Troyer’ citrange (CTTR) – 013 (TSKFL x CTTR – 013), common ‘Sunki’ mandarin (TSKC) with ‘Argentina’ citrange (CTARG) – 019 (TSKC x CTARG – 019), TSKC with ‘Swingle’ citrumelo (CTSW) – 031 (TSKC x CTSW – 031), and the trifoliate hybrid (HTR) - 069, as well as the varieties Volkamer lemon and Santa Cruz Rangpur lime. When grafted with ‘Tahiti’ acid lime, the rootstocks displaying the less sensitive to salinity were TSKFL x CTTR - 013 and TSKC x CTARG - 019.

Rootstocks of ‘Rangpur’ Lime and ‘Swingle’ Citrumelo were grown in containers with substrate in a greenhouse, aiming to evaluate the effects of N (urea) fertilization on the vegetative growth and macronutrient content of the plant tissue. The experimental design was a factorial randomized block design with four repetitions, and each experimental plot was composed of five plants. Four doses of N (0, 2.0, 4.0 and 8.0 g.plant-1) were evaluated and applied every week (15 applications) to both of the rootstocks. After 200 days of transplanting, the following parameters were evaluated: vegetative growth and total content of macronutrients on the dry weight of the leaves, stems, and roots. ‘Rangpur’ Lime was more vigorous that ‘Swingle’ Citrumelo. ‘Rangpur’ Lime showed the greatest accumulation of plant dry weight with 3.38 g.plant-1 of N and a greater root dry weight with 2.03 g.plant-1. For ‘Swingle’ Citrumelo, 2.03 g.plant-1 of N provided a greater plant dry weight, however, nitrogen fertilization reduced the root:canopy ratio of the rootstocks. The leaf content of N and P were favored by high doses of N in the tested range. Intermediate doses favored the Ca and Mg leaf contents. The leaf K content was decreased by nitrogen fertilization.

Abstract This study aimed to determine carbohydrates and organic acids in fruit from ‘Salustiana’ orange tree [Citrus sinensis (L.) Osb.] grafted onto different rootstocks using the HPLC technique, as well as to evaluate their physicochemical properties. As rootstocks, we tested ‘Rangpur’ lime, ‘Cleopatra’ mandarin, ‘Sunki’ mandarin, ‘Swingle’ citrumelo, and ‘C-13’ citrange. Fully mature fruit was first characterized according to their physicochemical parameters as fruit mass, longitudinal and equatorial diameters, peel color, juice yield, soluble solids, titratable acidity, and ratio. Then, freshly squeezed juice was used to determine and to quantify organic acids and carbohydrates by the HPLC system. All analyses were performed in triplicate complete randomized with five treatments (rootstocks). Fruit from all evaluated rootstocks presented adequate physicochemical attributes, meeting the quality standards of the citrus industry. ‘C-13’ citrange induced in a production of large-sized fruit whereas ‘Rangpur’ lime promoted higher soluble solids content in its juice. Significant differences were not observed between the treatments with regards to organic acids and carbohydrates concentrations. Citric and ascorbic acids were identified and quantified in the juice samples. The sugars identified were sucrose, glucose, and fructose. Organic acids and carbohydrates concentrations are consistent with those reported in the literature for citrus juice, providing information about nutrition and quality of ‘Salustiana’ sweet orange produced onto different rootstocks.

The EFSA Panel on Plant Health performed a pest categorisation of Diaphorina citri (Hemiptera: Liviidae) (Asian citrus psyllid) for the EU. D. citri is a key pest of citrus in several countries as it is a vector of serious bacterial pathogens, the putative causal agents of Huanglongbing (HLB) also known as citrus greening. Eggs are laid on tips of growing shoots on and between unfurling leaves. Females may lay more than 800 eggs during their lives. Nymphs pass through five instars. The life cycle requires from 14 to 49 days, depending upon the season. There is no diapause, but populations are low in winter. It overwinters as an adult which may live for several months. The species completes 9-10 generations/year; however, under protected conditions, up to 16 generations have been recorded. Commission Implementing Regulation (EU) 2019/2072 (Annex IIA) regulates D. citri, as a quarantine pest not known to occur in the EU territory. Fruits and plants for planting provide potential pathways for entry into the EU. Climatic conditions and the availability of host plants provide conditions to support establishment in the EU. The introduction of D. citri would have an economic impact in the EU through direct but mainly indirect effects due to potential transmission of HLB. Phytosanitary measures are available to reduce the likelihood of entry. D. citri satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. D. citri does not meet the criteria of occurring in the EU, nor plants for planting being the principal means of spread, for it to be regarded as a potential Union regulated non-quarantine pest. [ABSTRACT FROM AUTHOR]

Arid and semiarid regions are vulnerable to water deficits and salinity. Citrus plants are sensitive to saline stress and require the use of tolerant scion-rootstock combinations. Thus, this study aimed to evaluate and classify citrus scion-rootstock combinations with respect to their tolerance to salinity during seedling formation in a protected environment. An experiment was conducted in a randomized block design with a 5 x 12 x 2 factorial scheme corresponding to five levels of water salinity (0.8, 1.6, 2.4, 3.2, and 4.0 dS m-1) applied in 12 citrus rootstocks grafted with two scion varieties: 'Tahiti' acid lime and 'Star Ruby' grapefruit. The scion-rootstock combinations were evaluated for accumulated dry matter and survival index at 330 days after sowing the rootstocks. Salinity exerted different effects on the dry matter formation of scion-rootstock combinations. 'Star Ruby' was less sensitive to salinity, particularly when the rootstocks were the hybrids from 'Sunki of Florida' mandarin (TSKFL) with 'Troyer' citrange (CTTR) -- 013 (TSKFL x CTTR -- 013), common 'Sunki' mandarin (TSKC) with 'Argentina' citrange (CTARG) -- 019 (TSKC x CTARG -- 019), TSKC with 'Swingle' citrumelo (CTSW) -- 031 (TSKC x CTSW -- 031), and the trifoliate hybrid (HTR) - 069, as well as the varieties Volkamer lemon and Santa Cruz Rangpur lime. When grafted with 'Tahiti' acid lime, the rootstocks displaying the less sensitive to salinity were TSKFL x CTTR - 013 and TSKC x CTARG - 019. [ABSTRACT FROM AUTHOR]

This study evaluated oviposition of citrus leaf miner (CLM), Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), in different Citrus genotypes and related genera to search for resistance sources of type antixenosis or no preference for oviposition. Initially, we screened 23 genotypes and we used lime 'Rugoso' (Citrus jambhiri Lush.) as the susceptibility standard. Based on the number of eggs and pupae found on the plants, five genotypes were most promising to significantly reduce pest population: trifoliata 'Limeira' (Poncirus trifoliata), hybrids M x P222 [Citrus sinensis × Tangor Murcott (Citrus sinensis × C. reticulata)], C x R4 (Citrus sunki × P. trifoliata) and C x R315 (C. sunki × P. trifoliata) and tangerine 'Sunki' (C. sunki). In the preference test for oviposition with choice, trifoliata 'Limeira' and hybrid C x R315 were the least preferred genotypes by CLM, while in the no choice test, the effect of the genotypes was less evident, with a difference only between trifoliata 'Limeira' (less oviposited) and lime 'Rugoso' (more oviposited). Thus, trifoliata 'Limeira' and hybrid C x R315 are potential sources of antixenosis resistance and could be used in breeding programs to incorporate CLM resistance factors in improved genotypes. [ABSTRACT FROM AUTHOR]

Citrus relatives are a relevant source of valuable traits for use in citrus breeding, including resistance to diseases such as Huanglongbing (HLB). Resistant rootstocks may impact tree responses to HLB. This requires graft compatibility, which has been poorly investigated within the Aurantioideae. In this study, the biometric characteristics and the anatomy of the graft union of 86 scion/rootstock combinations were assessed. This comprised 18 genotypes/species and 8 genera from Citrinae, Balsamocitrinae, and Clauseninae subtribes sensu Swingle and Reece. Most graft combinations were found to be noncompatible. Phylogenetic proximity did not ensure successful grafting as, for example, Orange jasmine autografts failed, whereas some intergeneric grafts were successful (>60% of graft-take). Plant scion height was directly related to graft-take, but the correlation between the scion and rootstock stem diameters was not a reliable indicator of graft compatibility. Rangpur/Tabog, Tabog/Rangpur, Wampee/Rangpur, Wampee/Pomeroy, Wampee/Swingle, Pomeroy/Wampee, and Swingle/Wampee were the most compatible intergeneric graft combinations. Graft-take success for this was at similar levels to those of sweet orange grafted on common citrus rootstocks. The position as a scion or rootstock in the combination affected the performance and was specific to the genotypes tested. The lack of differentiation between xylem-derived calli and the accumulation of phenolic compounds at the graft union were clear anatomical and biochemical markers, respectively, of incompatibility for most Aurantioideae combinations. In the field, within a set of the ten most promising combinations, Hamlin/Rangpur (control) was the only one that became infected by ‘Candidatus Liberibacter asiaticus’. This was first observed 12 months after planting. Overall, the assessment of biometric traits and anatomy of the graft union allowed Aurantioideae genotypes to be divided into four clusters, with respect to their graft compatibility, as follows: fully compatible with high graft-take and plant growth; potentially compatible with high graft-take but lower plant growth; partially incompatible with lower graft-take and poor plant growth; and fully incompatible with a complete absence of graft-take.

Brazil is the largest producer of sweet orange and its juice in the world. Extensive cultivated area is located under an Aw climate in the North–Northwest of the state of São Paulo and the Triângulo of Minas Gerais state, being subjected to severe drought events. Although 56% of the orchards are irrigated in these regions, there is a need for drought tolerant rootstocks as an alternative to traditional genotypes such as Rangpur lime and Volkamer lemon, which are susceptible to the endemic citrus sudden death disease (CSD). In this sense, the tree size and production of Valencia sweet orange grafted onto 23 rootstock genotypes were evaluated over a ten-year period in rainfed cultivation at 7.0 m × 3.0 m spacing. Most evaluated types resulted from the cross of Poncirus trifoliata with Citrus, but two interspecific hybrids of Citrus (Sunki mandarin × Rangpur lime hybrids), the Barnes trifoliate orange and a tetraploid selection of Swingle citrumelo were also tested. Tropical Sunki mandarin was used as the reference control. Those hybrids coming from the cross of Sunki × Flying Dragon induced large tree sizes to Valencia sweet orange as well as the other citrandarins, Tropical Sunki mandarin and the Sunki mandarin × Rangpur lime hybrids, whereas only the tetraploid Swingle citrumelo behaved as a dwarfing rootstock, decreasing the canopy volume by 77% compared to that induced by the most vigorous citrandarin 535. The citrandarins 543 and 602 and the citrange C38 induced the highest mean fruit production, 67.2 kg·tree−1, but they also caused pronounced alternate bearing and only the hybrid 543 led to a high production efficiency consistently. Graft incompatibility symptoms were not observed over the evaluation period, and the canopy shape of Valencia sweet orange was also influenced by the rootstocks tested. Two citrandarins and one citrange were selected as the most promising alternative rootstocks for Valencia sweet orange grown under an Aw climate, even though productivity would likely benefit from supplementary irrigation.

The rise in the productivity of sweet orange in Brazil has been related to the use of superior rootstocks and higher tree density, among other factors. In order to investigate whether the cropping system and the land use efficiency would benefit from more intensive cultivation, the performance of Valencia sweet orange was evaluated over nine years on four rootstocks, which induced contrasting vigor, at 513, 696 and 1000 trees·ha−1. Agronomic Institute of Campinas (IAC) 1697 and IAC 1710 citrandarins, and diploid and allotetraploid (4×) Swingle citrumelos were classified as semi-dwarfing, super-standard, standard, and dwarfing rootstocks, respectively. The fruit yield per tree was decreased at higher tree densities, notably for more vigorous rootstocks. Conversely, the cumulative productivity was increased over the evaluation period by 27% at 1000 trees·ha−1, irrespective of the rootstock, and the most vigorous rootstock resulted in 2.5 times higher production than the dwarfing one on average. Most fruit quality parameters were seldom influenced by the tree density, while the rootstock was a decisive factor in improving the quality and the soluble solids content. Dwarfing rootstocks allowed for harvesting 17% more fruit per minute by manual pickers. Because the tree row volume per area is lower with such rootstocks, even at higher tree density, spray volume can be reduced, although appropriate equipment should be developed for better spray coverage on smaller trees. Nine years after planting under strict vector control, the cumulative incidence of huanglongbing-symptomatic trees on IAC 1710 was double that on Swingle 4×. Taken together, the results suggested that the land use efficiency in the citrus industry can be further improved by planting vigorous rootstocks at moderate to high tree densities. Nevertheless, obtaining highly productive semi-dwarfing and dwarfing rootstocks is the sine qua non for making high-density pedestrian sweet orange orchards more profitable.

A large number of expressed sequences tags are available for Citrus spp., which provides an opportunity to understand genomic organization of the transcribed regions. Here, we report a detailed analysis of repetitive elements including tandem repeats (TRs) and transposable elements (TEs) in the transcribed region of the Citrus spp. On average, 22% of the expressed sequence tags (ESTs) contain TRs. The relative density of TR classes is highly taxon-specific. For instance, Citrus limonia has a high relative density of mononucleotide repeats, whereas dinucleotide repeats are rare. The proportions of 2–6, 7–30 and 31–50 bp repeats were almost identical in all studied species except for C. limonia and C. limettioides. We found that

Abstract Citriculture is an important agricultural activity worldwide, occupying a relevant position in Brazil among fruit tree production for both the fresh fruit market and the processing industry for concentrated orange juice export. Recent advances in the country’s citrus nursery tree production system have been essential to guarantee the efficiency and competitiveness of Brazilian citriculture. The implementation of strict laws and regulations to produce trees in protected environments and improvements in production techniques for basic citrus propagation materials and nursery trees in São Paulo state has excluded the insect vectors of destructive diseases such as citrus variegated chlorosis and huanglongbing, making this an innovative reference system for citrus propagation around the globe. The main aspects of these advances are presented and discussed in this review, including advances in propagation techniques, scion and rootstock selection, genetic characterization and certification, tree size standards, cultural practices such as irrigation and fertilization for the production of citrus propagation materials and nursery trees, and nursery management tools.

The objective of this study was to evaluate the ecophysiological behavior of ‘Tahiti’ acid lime/rootstock grafted on Sunki mandarin hybrids during the prefloration stage of the plants, in the field, under saline stress. The progenies originating from crossings of the ‘Sunki’ mandarin with ‘Rangpur’ lime and Poncirus trioliata, as rootstocks, combined with the ‘Tahiti’ acid lime as a scion. The experiment was carried out under field conditions, at the Federal University of Campina Grande (UFCG), Pombal PB fields. In drainage lysimeter of 150 dm3, studying 10 scion/rootstock combinations, irrigated with two water salinity levels (CEa) (S1 = 0.3 and S2 = 3.0 dS m-1) making a 10 x 2 factorial scheme. The experimental design was a randomized block design, with 3 replicates and each plot consisting of a useful plant, totalizing 60 parcels. The scion/rootstock plants were transplanted at one year of age from the rootstocks sowing, being the beginning of the applications of the saline stress to the 15 days after the transplant lasting until the period of flowering, that is, up to 195 days after transplanting, During this period the plants were analyzed for growth and chlorophyll fluorescence a. The combinations less sensitive to salinity were composed of the ‘Tahiti’ grafted with TSKFL x (LCR x TR) - 018, TSKFL x TRBK - 011 and TSKFL x TRBK - 030, it being possible to use saline water with up to 3.0 dS m-1 in irrigation. Salinity did not damage the biochemical phase of the scion/rootstock combinations, only affecting the initial fluorescence of the lighted tissue.