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Summary: Pummelo (Citrus maxima) is one of the most important citrus crops and have genetically contributed sweet orange, lemon and most citrus cultivars. It has been cultivated for c. 4000 years in China and is also distributed in many Southeast Asian countries. Nevertheless, the origin and dispersal of pummelo remain elusive.We conducted whole‐genome sequencing for 290 pummelo accessions from China and Southeast Asia (SEA). Our findings indicated that pummelo was originated in Yunnan province. The divergence of the China‐SEA accessions occurred c. 2000 years ago and the divergence was likely facilitated through the Maritime Silk Road.We detected the divergence of genomic regions associated with fruit flavor and color, indicating different selection by human activities in different regions. A gene encoding lycopene cyclase 2 (LCYB2) exhibited a high degree of divergence in expression and sequence between red‐flesh and white‐flesh pummelos. A SNP in the coding region of LCYB2 resulted in a reduction in lycopene β‐cyclizing enzyme activity, leading to the accumulation of lycopene and the development of the red‐flesh trait.This study reveals the origin and evolutionary history of pummelo and provides insights into the genomic basis for the divergence of fruit flavor and color. [ABSTRACT FROM AUTHOR]

The flesh color of pummelo (Citrus maxima) fruits is highly diverse and largely depends on the level of carotenoids, which are beneficial to human health. It is vital to investigate the regulatory network of carotenoid biosynthesis to improve the carotenoid content in pummelo. However, the molecular mechanism underlying carotenoid accumulation in pummelo is not fully understood. In this study, we identified a novel histone methyltransferase gene, CgSDG40, involved in carotenoid regulation by analyzing the flesh transcriptome of typical white-fleshed pummelo, red-fleshed pummelo and extreme-colored F1 hybrids from a segregated pummelo population. Expression of CgSDG40 corresponded to flesh color change and was highly coexpressed with CgPSY1. Interestingly, CgSDG40 and CgPSY1 are located physically adjacent to each other on the chromosome in opposite directions, sharing a partially overlapping promoter region. Subcellular localization analysis indicated that CgSDG40 localizes to the nucleus. Overexpression of CgSDG40 significantly increased the total carotenoid content in citrus calli relative to that in wild type. In addition, expression of CgPSY1 was significantly activated in overexpression lines relative to wild type. Taken together, our findings reveal a novel histone methyltransferase regulator, CgSDG40, involved in the regulation of carotenoid biosynthesis in citrus and provide new strategies for molecular design breeding and genetic improvement of fruit color and nutritional quality.

In the framework of our studies on Citrus cultivars in Greece, the chemical composition of the essential oils (EOs) from the peels and leaves of orange, pummelo, and tangelo (mandarin × grapefruit hybrid) cultivated in Greece have been studied. All EOs have been analyzed through GC-MS, and a total of 47 and 87 metabolites were identified in the peels and leaves, respectively. These metabolites are classified into the chemical groups of terpenes, alcohols, aldehydes, esters, ketones, and organic acids. Limonene was the most abundant compound in the peel EOs. Moreover, bioactive polymethoxyflavones (PMFs) were isolated and structurally determined from the peels of orange and tangelo, highlighting them as a good potential source of natural PMFs. All EOs were evaluated for their antimicrobial activity against nine human pathogenic microorganisms (six bacteria and three fungi), showing an interesting profile. The EOs from the peels of all Citrus species exhibited a stronger antimicrobial activity compared to those from the leaves. The susceptibility of the assayed Gram-positive bacteria was observed to be greater than that of Gram-negative bacteria, while the fungi were also relatively less resistant than bacteria. The rootstock choice did not influence the EO profile of the fruit peel but exerted an influence on the chemical profile of the leaves. [ABSTRACT FROM AUTHOR]

Research backgroundThere is considerable diversity in newly developed pummelo × sweet orange citrus hybrids. Most hybrids showed lower peel thickness and high juice yield but there is a lack of information on fruit quality parameters and molecular characterization. Therefore, the aim of the current study is to determine the content of antioxidants and properties of the fresh juice of 24 new pummelo × sweet orange citrus hybrids (Citrus maxima [Burm. f.] Osbeck × Citrus sinensis [L.] Osbeck) and the parental genotypes along with molecular characteristics determined using acidity specific markers. Experimental approach. The correlation and estimate of inheritance of the fruit juice properties: ascorbic acid, total phenol, total flavonoid, total antioxidant, total soluble solid and sugar contents, pH, titratable acidity, along with sensory evaluation was performed. Molecular characterization of these hybrids was carried out using de novo generated acidity specific simple sequence repeat (SSR) markers. Results and conclusions. The main constituents of the fruit juice of pummelo × sweet orange hybrids were observed in the range of w(ascorbic acid)=40.00–58.13 mg/100 g, total phenols expressed as gallic acid equivalents w(GAE)=40.67–107.33 mg/100 g, total antioxidants expressed as Trolox equivalents b(Trolox)=2.03–5.49 µmol/g, total flavonoids expressed as quercetin equivalents w(QE)=23.67–59.33 mg/100 g, along with other properties: total soluble solids=7.33–11.33 %, w(total sugar)=2.10–5.76 %, w(reducing sugar)=1.69–2.78 %, w(non-reducing sugar)=0.39–3.17 % and titratable acidity 1.00–2.11 %. The above parameters differed significantly in the fruit juice of the evaluated pummelo × sweet orange hybrids. Considering these parameters, the hybrids SCSH 17-9, SCSH 13-13, SCSH 11-15 and SCSH 3-15 had superior antioxidant properties in terms of these parameters. A higher heritability (≥80 %) was also observed for all juice properties. Molecular characterization of pummelo × sweet orange hybrids showed that >50 % of the hybrids were grouped with medium acidity parents. Both molecular and biochemical parameter-based clustering showed that interspecific hybrids exhibit transgressive segregation with increased antioxidants that help alleviate the health problems. Novelty and scientific contribution. These newly developed pummelo × sweet orange citrus hybrids are a valuable source of high-quality antioxidants for a healthy diet. The identification of trait markers that enable selection at the seedling stage is of great benefit to citrus breeders, as the characteristic features of a mature tree are not yet visible at the juvenile stage.

Research background. There is considerable diversity in newly developed pummelo x sweet orange citrus hybrids. Most hybrids showed lower peel thickness and high juice yield but there is a lack of information on fruit quality parameters and molecular characterization. Therefore, the aim of the current study is to determine the content of antioxidants and properties of the fresh juice of 24 new pummelo x sweet orange citrus hybrids (Citrus maxima [Burm. f.] Osbeck x Citrus sinensis [L.] Osbeck) and the parental genotypes along with molecular characteristics determined using acidity specific markers. Experimental approach. The correlation and estimate of inheritance of the fruit juice properties: ascorbic acid, total phenol, total flavonoid, total antioxidant, total soluble solid and sugar contents, pH, titratable acidity, along with sensory evaluation was performed. Molecular characterization of these hybrids was carried out using de novo generated acidity specific simple sequence repeat (SSR) markers. Results and conclusions. The main constituents of the fruit juice of pummelo x sweet orange hybrids were observed in the range of w(ascorbic acid)=40.00-58.13 mg/100 g, total phenols expressed as gallic acid equivalents w(GAE)=40.67-107.33 mg/100 g, total antioxidants expressed as Trolox equivalents b(Trolox)=2.03-5.49 μmol/g, total flavonoids expressed as quercetin equivalents w(QE)=23.67-59.33 mg/100 g, along with other properties: total soluble solids=7.33-11.33 %, w(total sugar)=2.10-5.76 %, w(reducing sugar)= 1.69-2.78 %, w(non-reducing sugar)=0.39-3.17 % and titratable acidity 1.00-2.11 %. The above parameters differed significantly in the fruit juice of the evaluated pummelo x sweet orange hybrids. Considering these parameters, the hybrids SCSH 17-9, SCSH 13-13, SCSH 11-15 and SCSH 3-15 had superior antioxidant properties in terms of these parameters. A higher heritability (≤80 %) was also observed for all juice properties. Molecular characterization of pummelo x sweet orange hybrids showed that >50 % of the hybrids were grouped with medium acidity parents. Both molecular and biochemical parameter-based clustering showed that interspecific hybrids exhibit transgressive segregation with increased antioxidants that help alleviate the health problems. Novelty and scientific contribution. These newly developed pummelo x sweet orange citrus hybrids are a valuable source of high-quality antioxidants for a healthy diet. The identification of trait markers that enable selection at the seedling stage is of great benefit to citrus breeders, as the characteristic features of a mature tree are not yet visible at the juvenile stage. [ABSTRACT FROM AUTHOR]

In the framework of our studies on Citrus cultivars in Greece, the chemical composition of the essential oils (EOs) from the peels and leaves of orange, pummelo, and tangelo (mandarin × grapefruit hybrid) cultivated in Greece have been studied. All EOs have been analyzed through GC-MS, and a total of 47 and 87 metabolites were identified in the peels and leaves, respectively. These metabolites are classified into the chemical groups of terpenes, alcohols, aldehydes, esters, ketones, and organic acids. Limonene was the most abundant compound in the peel EOs. Moreover, bioactive polymethoxyflavones (PMFs) were isolated and structurally determined from the peels of orange and tangelo, highlighting them as a good potential source of natural PMFs. All EOs were evaluated for their antimicrobial activity against nine human pathogenic microorganisms (six bacteria and three fungi), showing an interesting profile. The EOs from the peels of all Citrus species exhibited a stronger antimicrobial activity compared to those from the leaves. The susceptibility of the assayed Gram-positive bacteria was observed to be greater than that of Gram-negative bacteria, while the fungi were also relatively less resistant than bacteria. The rootstock choice did not influence the EO profile of the fruit peel but exerted an influence on the chemical profile of the leaves.

Summary: Pummelo (Citrus maxima or Citrus grandis) is a basic species and an important type for breeding in Citrus. Pummelo is used not only for fresh consumption but also for medicinal purposes. However, the molecular basis of medicinal traits is unclear. Here, compared with wild citrus species/Citrus‐related genera, the content of 43 bioactive metabolites and their derivatives increased in the pummelo. Furthermore, we assembled the genome sequence of a variety for medicinal purposes with a long history, Citrus maxima 'Huazhouyou‐tomentosa' (HZY‐T), at the chromosome level with a genome size of 349.07 Mb. Comparative genomics showed that the expanded gene family in the pummelo genome was enriched in flavonoids‐, terpenoid‐, and phenylpropanoid biosynthesis. Using the metabolome and transcriptome of six developmental stages of HZY‐T and Citrus maxima 'Huazhouyou‐smooth' (HZY‐S) fruit peel, we generated the regulatory networks of bioactive metabolites and their derivatives. We identified a novel MYB transcription factor, CmtMYB108, as an important regulator of flavone pathways. Both mutations and expression of CmtMYB108, which targets the genes PAL (phenylalanine ammonia‐lyase) and FNS (flavone synthase), displayed differential expression between Citrus‐related genera, wild citrus species and pummelo species. This study provides insights into the evolution‐associated changes in bioactive metabolism during the origin process of pummelo. [ABSTRACT FROM AUTHOR]

The nutritional and volatile profiles of pulp and flavedo samples from four distinct local pummelo landraces ("Siji," "Pingshan," "Wendan," and "Guanxi") cultivated in Fujian province of China were investigated. "Guanxi" pummelo exhibited relatively high contents of vitamin C (42.01 mg/100 mL) and phenols (360.61 mg/L) and displayed a robust antioxidant capacity (41.15 mg/100 mL). Conversely, the red pulp from "Pingshan" demonstrated relatively high values of carotenoids (55.96 µg/g) and flavonoids (79.79 mg/L). Considerable differences were observed in volatile compositions between the two fruit tissues and among the four genotypes. A total of 166 and 255 volatile compounds were detected in the pulp and flavedo samples, respectively. Notably, limonene and β‐myrcene were identified as the principal volatile compounds in flavedo, whereas hexanal was highly abundant in the pulp of "Siji," "Pingshan," and "Guanxi." "Wendan" displayed distinct separation from the other three pummelo cultivars in principal component analysis based on the pulp volatile compositions. This distinction was attributed to the higher number and content of volatile compounds in "Wendan" pulp, particularly the remarkable enrichment of β‐myrcene. The newly characterized pummelo landraces and genotype/tissue‐dependent variations in volatiles provide essential information for the genetic improvement of pummelo aroma, as well as for fruit processing and utilization. [ABSTRACT FROM AUTHOR]

A study was conducted to determine the mineral nutrients concentration in the index leaf of pummelo accessions. Index leaf samples from 25 pummelo accessions grafted on pummelo and 12 pummelo clones grafted on Rangpur lime rootstocks were collected for assessing leaf mineral nutrient status. The results revealed that pummelo plants grafted on pummelo, the concentration of leaf N (1.43-2.49 %), P (0.17-0.22 %), K (0.75-4.45 %), Ca (2.37-6.29 %), Mg (0.60-1.04 %), S (0.06-0.22 %), Fe (124-245.45 mg kg-1), Mn (9.85-50.05 mg kg-1), Zn (17-69 mg kg-1) and Cu (8.8-25.15 mg kg-1) showed significant variation with different accessions. Out of 25 pummelo accessions, twenty-four accessions were deficient in N and S, fourteen were deficient in K, four were deficient in Mn and five were deficient in Zn and all accessions were sufficient in P, Ca, Mg, Fe and Cu. The observed trends in the leaf nutrient concentration of pummelo accessions clearly indicated the significance of the genotypic variation when chemical analysis is used for diagnosing the leaf nutrient status of pummelo trees. Similarly, leaf N, P, K, Ca, Mn, Cu and Zn varied significantly among twelve pummelo clones grafted on Rangpur lime. Among the clones grafted on Rangpur lime, 18-3 and 18-5 found to have higher and lower leaf nutrient content in most of the mineral nutrients, respectively. The leaf nutrient content of pummelo varies among genotypes, but there is no genotype that stands out in all macro and micronutrients evaluated. The N, P, K, Ca, S, Fe, Mn and Cu leaf contents in pummelo were always higher in plants grafted on Rangpur lime. However, the foliar Mg and Zn contents were continually higher in plants grafted on ‘pummelo’ compared to Rangpur lime which eventually reduces leaf yellowing/chlorosis in pummelo. Pummelo rootstocks were found to respond well in terms of Mg and Zn nutrient uptake and tolerance to Phytophthora as compared to Rangpur lime. Therefore, it is concluded that pummelo can be an ideal rootstock for commercial pummelo cultivation. [ABSTRACT FROM AUTHOR]

Although it is usually latent on citrus, apple, and pear, apple stem grooving virus (ASGV) poses a great risk to many sensitive cultivars. Since severe leaf yellow mottle mosaic (LYMM) symptoms have been observed on Huangjinmiyou (HJY) pummelos (Citrus grandis cv. Huangjinmiyou), a commercial variety that is widely cultivated in South China, high throughput sequencing (HTS) was used to find potential pathogens and only three divergent ASGV variants were identified. The three ASGV variants shared 81.03–82.34% genome-wide pairwise identities with each other, and were separately closest to other ASGV variants from different hosts and/or geographical regions, as indicated by viral phylogenies. However, these new variants may have developed from viral interstrain interactions, based on the results of recombination analysis. A large-scale survey using reverse transcription-PCR (RT-PCR) protocols designed for the three ASGV variants revealed a high incidence (92.7–100%) of ASGV in symptomatic HJY trees from 11 major citrus-producing regions in China. None of ASGV were detected in asymptomatic trees. Temperature treatments applied to the symptomatic HJY plants showed that ASGV is sensitive to high temperatures (30–35°C), at which not only the plants recovered, but also the viruses were not detected by RT-PCR, while at low temperatures (20–24°C), both the symptoms and viruses remained detectable. These data show that ASGV is associated with the LYMM disease prevalent on HJY in China, and this is the significant basis especially of taking appropriate measures timely to manage the disease.

• A total of 102 pummelo hybrid progenies from two cross-combinations were evaluated. • Physico-chemical fruit quality and sensory properties varied significantly. • Clustering and principal component analysis help to identify groups among progeny. • Correlation analysis showed an association among fruit quality determinants. • Five hybrids were found promising with superior fruit quality traits. Pummelo is the largest fruit in the citrus family and has thick rind, unique flavour and other biochemical characteristics depending on the genotypes. The consumer preference mostly tends towards fruits with thin rind for easy separation of segments coupled with negligible bitterness. The present study was carried out on two pummelo hybrid progenies planted during August 2016 at Indian Institute of Horticultural Research(IIHR), Bengaluru, Karnataka, India. The morphological and biochemical characterization of 102 pummelo hybrids generated from two different cross combinations was conducted with special emphasis on economic traits (low in bitterness and thin rind). Among the progenies, two hybrid combinations, the fruit weight ranged from 0.72 to 2.62 kg in Acc.12 x Acc.19 with rind thickness ranging from 0.92 to 3.16 cm, while in Acc.3 x Acc.19, the fruit weight ranged from 0.61 to 2.41 kg with rind thickness ranging from 1.08 to 2.88 cm. The mean TSS was 8.80 and 9.02° B across two different cross combinations, respectively. The average titratable acidity ranged from 1.35 to 1.38 % and total flavonoid content of 13.71 and 11.44 mg catechin eqv.100 g-1 in the two hybrid progenies. Based on biochemical traits and sensory evaluations, the elite progenies H17–3, H17–5 and H17–9 from the first cross (Acc.12 x Acc.19) as well as H23–4 and H23–11 from the second cross (Acc.3 x Acc.19), were selected for their low bitterness and high TSS. These selections show potential as valuable breeding stock or new hybrids for commercial cultivation. [ABSTRACT FROM AUTHOR]

Citrus fruits produced in China are often affected by granulation. Granulation is an altered physiological state of citrus fruits occurring usually before harvest but whose underlying mechanisms remain elusive. In this study, cDNA-AFLP technology enabled the identification of 116 granulation-associated genes in pummelo (C. grandis) juice sacs. Differentially expressed transcript-derived fragments (TDFs) were shown to be mainly involved in biological regulation and signal transduction, carbohydrate and energy metabolism, nucleic acid, protein metabolism, stress responses, and cell metabolism. Therefore, granulation in pummelo juice sacs seems to involve the following alterations: (1) changes in hormone levels; (2) activation of metabolic pathways related to ATP and sugar synthesis to produce more energy; (3) nucleic acid accumulation and increased protein degradation; (4) activation of stress-responsive metabolic pathways; (5) accelerated juice sac senescence. Our findings provide an overview of differential responses occurring at the transcriptional level in granulated juice sacs, thus revealing new insights into the adaptive mechanisms underlying this altered physiological state in 'Guanximiyou' pummelo (C. grandis) juice sacs.

The study investigated the effect of albedo and flavedo extracts of grapefruit and pomelo on storage stability of turkey patties during refrigerated storage. Five different types of products were developed depending on the addition of extracts viz. control (C), albedo and flavedo extract of grapefruit (GA and GF), and albedo and flavedo extract of pomelo (PA and PF). The products were stored for 10 days and evaluated for lipid and protein oxidation, pH, colour and sensory properties. The extracts improved the lipid oxidative stability by decreasing (P < 0.05) the TBARS values of the samples compared to control group. No effect of the extract treatments (P > 0.05) was observed on pH and colour values of the products (a* and b*). The lowest TBARS values were found for the products containing GF (0.78 mg MA/kg) on day 4. The treatments showed a significant impact on flavour of the products and the highest scores were obtained for PA containing products. [ABSTRACT FROM AUTHOR]

Objectives: To verify the level of oxidation of biomolecules in the peripheral blood of obese patients before and after incubation with the pummelo pulp extract at 25 mg/mL., Methods: This investigation included 241 individuals, distributed across the following groups: control (n = 69; 30 men and 39 women); pre-obesity (n = 78; 29 men and 49 women); level I obesity (n = 62; 20 men and 42 women); and level II or III obesity (n = 32; 11 men and 21 women)., Results: TBARS and MN levels were significantly altered by incubation with pummelo extract in both genders and in all the groups according to their obesity level. Another alteration in the antioxidant profile of the samples was a significant increase in vitamin C levels observed after incubation with pummelo extract in all experimental groups., Conclusions: The aqueous extract of pummelo pulp showed in vitro biological activity against the oxidation of biomolecules, suggesting that its bioactive compounds may bring health benefits of obese patients., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Mutation breeding is a key method of generating a large number of heritable variations. Effective dose (LD50) needs to be standardized for inducing sufficient variation in a crop. In the present study, seeds were irradiated with different doses of Gamma rays and found that 66.94 Gy could suppress germination close to 50 percent (LD50) in pummelo. This 60 Gy gamma dose can effectively be used for raising the mutant populations to identify a desirable mutation in pummelo.

Citrus genus is notable for peel essential oils which are valuable by-products during Citrus processing. In this study, it was aimed to determine chemical composition and antimicrobial activity of the essential oil of pummelo peel (PEO). The essential oil was obtained by hydrodistillation from flavedo layer of the peel. It was subjected to Gas Chromatography/Mass Spectrometry (GC/MS) for identification of its volatiles and a total of sixty-two compounds were identified. Monoterpenes constituted 89.36% of PEO, mostly by D-limonene (76.97%) and β-myrcene (6.37%). The essential oil became prominent especially with its nootkatone content (1.13%). In antimicrobial activity assays, broth macrodilution method was used against to Staphylococcus aureus, Bacillus cereus, Escherichia coli, Salmonella Enteritidis, Saccharomyces cerevisiae and Candida albicans. According to the test results, minimum inhibitory concentrations of the essential oil ranged between 2000 and 16000 µg/mL for S. aureus, B. cereus, S. cerevisiae and C. albicans. No inhibitory effect was observed on E. coli and S. Enteritidis although 32000 µg/mL PEO was applied. On the basis of the results obtained, it was thought that PEO could be used as a natural and inexpensive flavouring and antimicrobial agent by the food and pharmaceutical industries via valorization of pummelo peel. [ABSTRACT FROM AUTHOR]

Guijie Li,1,* Yujiao Cheng,1,* Tenghui Zhang,2 Yingzhuo Li,3 Leng Han,1 Guolu Liang4 1Citrus Research Institute, Southwest University, Chongqing, People’s Republic of China; 2Chengdu Centre Testing International Group Co., Ltd., Chengdu, People’s Republic of China; 3Chongqing Beibei Agricultural and Rural Committee, Chongqing, People’s Republic of China; 4College of Horticulture and Landscape Architecture, Southwest University, Chongqing, People’s Republic of China*These authors contributed equally to this workCorrespondence: Leng HanCitrus Research Institute, Southwest University, No. 15 Ganjucun, Xiema, Beibei District, Chongqing, 400712, People’s Republic of ChinaEmail hanleng5@cric.cnGuolu LiangCollege of Horticulture and Landscape Architecture, Southwest University, No. 2 Tiansheng Road, Beibei District, Chongqing, 400715, People’s Republic of ChinaEmail lianggl@swu.edu.cnPurpose: Citrus essential oils are widely used for aromatherapy and the alternative treatment of chronic diseases. Beyond the aroma substances, they are known to contain bioactive nonvolatile components; however, little knowledge has been gained about nonvolatiles in the essential oil of pomelo (Citrus grandis Osbeck), the largest citrus fruit. The purpose of this study was to analyze the nonvolatile oxygenated heterocyclic compounds (OHCs) of pomelo essential oils and evaluate their in vitro antioxidant activities for further development.Methods: Cold-pressed essential oil (CPEO) and distilled essential oil (DEO) were obtained from the peel of the Liangping pomelo cultivar. High-performance liquid chromatography (HPLC) coupled with a photodiode array and fluorescence detection method was developed to identify and quantify the OHCs of the two essential oils. Ferric reducing antioxidant power and 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide (PTIO) radical scavenging assays were used to determine the antioxidative capabilities.Results: Thirteen OHCs were identified in CPEO. Coumarins such as meranzin (2.0 mmol L− 1) and furanocoumarins such as isoimperatorin (1.3 mmol L− 1) composed the majority of nonvolatiles in CPEO. These OHCs were characterized by high proportion (58%) of side chain epoxides. Five OHCs, namely, auraptenol, 6ʹ,7ʹ-dihydroxybergamottin (6ʹ,7ʹ-DHB), imperatorin, isoimperatorin and 8-geranyloxypsoralen were first identified in pomelo CPEO. Eight OHCs were detected at trace amounts in pomelo DEO. Antioxidant assays showed that CPEO was multiple times more potent than DEO regarding the total reducing power and radical scavenging capacity. Clearance of PTIO, a stable reactive oxygen species, followed slow kinetics.Conclusion: Coumarins and furanocoumarins, two families of OHCs, constituted most of the nonvolatile components in CPEO. The nonvolatiles contributed significantly to the in vitro antioxidant activity of CPEO. Pomelo CPEO showed good prospects as a potential long-lasting natural antioxidant.Keywords: volatile oil, cold expression, hydrodistillation, psoralen, epoxides, fluorescence, radical scavenging, pummelo, Citrus maxima

We identified eight local citrus accessions grown on Kuroshima Island (approx. N 30°, E 129°, 15 km2), Kagoshima Prefecture. Cleaved amplified polymorphic sequence (CAPS) analysis and fruit characteristic investigation were combined for their identification. The results were as follows: 'Kuroshima-mikan' was Shimamikan (Amami Oshima) (Citrus sp.), 'Kozumikan' was Shiikuwasha (C. depressa), 'Hachigatsu-mikan' was Kabuchii (C. keraji), 'Kawabata' (B) was Kawabata-mikan (C. aurea), 'Kinebu' was Kunenbo (C. nobilis), 'Yurimikan' was citron (C. medica), and 'Akamikan' was pummelo (C. maxima). Although 'Kawabata' (A) was closely related to the Chinese mandarin C. sunki, it was not clear whether they were the same. Although Kuroshima is small, it was identified as an island with various local citrus genetic resources. [ABSTRACT FROM AUTHOR]

Red-fleshed pummelo (Citrus grandis), a mutant of ‘Guanxi’, is an important economic plant rich in carotenoids. The transcriptome of ‘Guanxi’ pummelo was compared with red-fleshed pummelo, with the aim of identifying the key genes responsible for red flesh through RNA sequencing. In total, 44.11 and 47.71 Gb clean reads were respectively obtained after filtering in red and white flesh. Altogether 46,425 unigenes, with an average length of 1208 bp, were assembled. Compared with that of white flesh, 3722 genes were up-regulated, whereas 1421 genes appeared down-regulated in the red-fleshed pummelo. A GO analysis assigned 11,983 differentially expressed genes to 53 subcategories, and 3582, 4722 and 3679 differentially expressed genes were involved in biological processes, cellular components and molecular functions, respectively. The mevalonate pathway involved in terpenoid backbone biosynthesis was significantly different between ‘Guanxi’ pummelo and its red-fleshed mutant, and the differences were closely associated with carotenoid biosynthesis. The expression levels of the carotenoid biosynthetic pathway genes were different between ‘Guanxi’ pummelo and its red-fleshed mutant, with the upstream genes having higher expression levels in red-fleshed pummelo than in ‘Guanxi’ pummelo, whereas the downstream gene β-CHX was downregulated. Two bHLH transcription factors (CL4778.Contig1 and CL4778.Contig2) were of the same branch as CubHLH1, regulating carotenoid biosynthesis in Citrus unshiu Marc., and Unigene CL4778.Contig2 had expression differences in two kinds of pummelo, which suggested CL4778.Contig2 should be a candidate gene controlling carotenoid accumulation in red pummelo. The study would be beneficial to identify the major gene regulating the red flesh trait.

The selection of elite bud-sports is an important breeding approach in horticulture. We discovered and evaluated a thornless pummelo bud-sport (TL) that grew more vigorously and was more tolerant to Huanglongbing (HLB) than the thorny wild type (W). To reveal the underlying molecular mechanisms, we carried out whole-genome sequencing of W, and transcriptome comparisons of W, TL, and partially recovered thorny “mutants” (T). The results showed W, TL, and T varied in gene expression, allelic expression, and alternative splicing. Most genes/pathways with significantly altered expression in TL compared to W remained similarly altered in T. Pathway and gene ontology enrichment analysis revealed that the expression of multiple pathways, including photosynthesis and cell wall biosynthesis, was altered among the three genotypes. Remarkably, two polar auxin transporter genes, PIN7 and LAX3, were expressed at a significantly lower level in TL than in both W and T, implying alternation of polar auxin transport in TL may be responsible for the vigorous growth and thornless phenotype. Furthermore, 131 and 68 plant defense-related genes were significantly upregulated and downregulated, respectively, in TL and T compared with W. These genes may be involved in enhanced salicylic acid (SA) dependent defense and repression of defense inducing callose deposition and programmed cell death. Overall, these results indicated that the phenotype changes of the TL bud-sport were associated with tremendous transcriptome alterations, providing new clues and targets for breeding and gene editing for citrus improvement.

The selection of elite bud-sports is an important breeding approach in horticulture. We discovered and evaluated a thornless pummelo bud-sport (TL) that grew more vigorously and was more tolerant to Huanglongbing (HLB) than the thorny wild type (W). To reveal the underlying molecular mechanisms, we carried out whole-genome sequencing of W, and transcriptome comparisons of W, TL, and partially recovered thorny "mutants" (T). The results showed W, TL, and T varied in gene expression, allelic expression, and alternative splicing. Most genes/pathways with significantly altered expression in TL compared to W remained similarly altered in T. Pathway and gene ontology enrichment analysis revealed that the expression of multiple pathways, including photosynthesis and cell wall biosynthesis, was altered among the three genotypes. Remarkably, two polar auxin transporter genes, PIN7 and LAX3, were expressed at a significantly lower level in TL than in both W and T, implying alternation of polar auxin transport in TL may be responsible for the vigorous growth and thornless phenotype. Furthermore, 131 and 68 plant defense-related genes were significantly upregulated and downregulated, respectively, in TL and T compared with W. These genes may be involved in enhanced salicylic acid (SA) dependent defense and repression of defense inducing callose deposition and programmed cell death. Overall, these results indicated that the phenotype changes of the TL bud-sport were associated with tremendous transcriptome alterations, providing new clues and targets for breeding and gene editing for citrus improvement. [ABSTRACT FROM AUTHOR]

Delayed greening of young leaves is an unusual phenomenon of plants in nature. Citrus are mostly evergreen tree species. Here, a natural mutant of "Guanxi" pummelo (Citrus maxima), which shows yellow leaves at the young stage, was characterized to identify the genes underlying the trait of delayed leaf greening in plants. A segregating population with this mutant as the seed parent and a normal genotype as the pollen parent was generated. Two DNA pools respectively from the leaves of segregating seedlings with extreme phenotypes of normal leaf greening and delayed leaf greening were collected for sequencing. Bulked segregant analysis (BSA) and InDel marker analysis demonstrated that the delayed leaf greening trait is governed by a 0.3 Mb candidate region on chromosome 6. Gene expression analysis further identified a key candidate gene (Citrus Delayed Greening gene 1, CDG1) in the 0.3 Mb region, which showed significantly differential expression between the genotypes with delayed and normal leaf greening phenotypes. There was a 67 bp InDel region difference in the CDG1 promoter and the InDel region contains a TATA-box element. Confocal laser-scanning microscopy revealed that the CDG1-GFP fusion protein signals were co-localized with the chloroplast signals in the protoplasts. Overexpression of CDG1 in tobacco and Arabidopsis led to the phenotype of delayed leaf greening. These results suggest that the CDG1 gene is involved in controlling the delayed leaf greening phenotype with important functions in chloroplast development. [ABSTRACT FROM AUTHOR]

Pummelos and hybrids, such as grapefruits, have high furanocoumarin and low flavonoid contents. Furanocoumarins interact negatively with certain drugs, while flavonoids are antioxidant compounds with health benefits. To obtain new grapefruit-like varieties with low furanocoumarin and high flavonoid contents, diploid and triploid hybrid populations from crosses between diploid and tetraploid “Clemenules” clementine and diploid “Pink” pummelo were recovered and analyzed. With regard to furanocoumarins, triploids produce less bergapten, bergamottin and 6,7-DHB than diploids. Regarding flavonoids, triploids yielded more eriocitrin, narirutin, hesperidin and neohesperidin than diploids, whereas no differences were observed in neoeriocitrin and naringin. These results indicate that, the strategy to recover triploid hybrids by 4x × 2x crosses is more appropriate than the recovery of diploid hybrids by 2x × 2x crosses for obtaining grapefruit-like varieties of citrus with lower furanocoumarin and higher flavonoid contents.

Phytophthora species is the major threat for world citrus industry in general, and for India, in particular due to commercial use of susceptible rootstocks. The resistant gene possessed by Poncirus genus may be of immense use, if transferred in a well acclimatized citrus species which can have good impact on fruit size of scion varieties. Being a soil borne problem, development of resistant/tolerant rootstock(s) is the most eco-friendly solution to combat with this deadly disease. The present study was conducted during 2016 to understand the tolerance mechanism in the intergeneric hybrids of citrus rootstocks against Phytophthora nicotianae. The materials of study consisted of 30 hybrids, ten each of Pummelo (P) × Troyer (T), Pummelo (P) × Sacaton (S) and Pummelo (P) × Trifoliate orange (TO) were tested against the inoculation of P. nicotianae, taking Pummelo, Troyer and Citrumelo as control treatments. Of the total hybrid progenies, only six hybrids (P × TO-103, P × TO-112, P × S-117, P × S-119, P × T-125 and P × T-130) expressed resistance against P. nicotianae on the basis of lesion length (nil or <2.5 cm). Of the tested hybrids, P x S-117 had the highest photosynthetic rate (A) (8.12 µmol m-1s-1) followed by P × TO-112 and P × s-119. Excised leaf water loss (ELWL) was lowest in P × S -119 (7.47%) without having significant diference with Troyer citrange, and rest of the resistant hybrids. The highest relative leaf water content (RWC) was registered in P × T-125 (84.47%), which was similar statistically with P × T-119, P × T-103 and P × T-112 (77.59-83.42%) hybrids. Hybrid P × S -117 tended to show the highest total chlorophyll content (12.14 mg g-1FW), followed by P × TO-112 and P × T-127. P × s-117 expressed the lowest level of hydrogen peroxide (100.72 mM mg-1 FW) without having any significant difference with those of P × TO-110, P × T-127 and P × T-130 hybrids. The lipid peroxidation was highest in P × T-132 (25.99 µmol g-1 FW), while its lowest accumulation was in P × s-119 (6.44 µmol g-1 FW) with statistically similar to P × T-130 hybrid. The highest content of glycine betain was noticed in P × TO-103, P × TO-117 and P × TO-130 (0.33 mg g-1 FW in each). Of the total hybrid progenies, highest accumulation of leaf N was found in P × T-125 (2.74%) followed by P × S -119 and P × T-130. All six resistant hybrids excelled over other hybrids in respect of leaf K+ content. The content of Ca+2 was highest in the leaves of P × s-117 (4.90%) having similarity statistically with P × T-125 (4.87%). The resistance of identified hybrids (P × TO-103, P × TO-112, P × s-117, P × s-119, P × T-125 and P × T-130) against P. nicotianae was also evidenced by low ROS generation and ELWL, with high RWC and leaf nutrient status over other hybrids. Among the various physicochemical characters studied, only A, ELWL and N were found to have significant but inverse relationship with lesion length caused by Phytophthora inoculation. [ABSTRACT FROM AUTHOR]

Pummelos and hybrids, such as grapefruits, have high furanocoumarin and low flavonoid contents. Furanocoumarins interact negatively with certain drugs, while flavonoids are antioxidant compounds with health benefits. To obtain new grapefruit-like varieties with low furanocoumarin and high flavonoid contents, diploid and triploid hybrid populations from crosses between diploid and tetraploid "Clemenules" clementine and diploid "Pink" pummelo were recovered and analyzed. With regard to furanocoumarins, triploids produce less bergapten, bergamottin and 6,7-DHB than diploids. Regarding flavonoids, triploids yielded more eriocitrin, narirutin, hesperidin and neohesperidin than diploids, whereas no differences were observed in neoeriocitrin and naringin. These results indicate that, the strategy to recover triploid hybrids by 4x × 2x crosses is more appropriate than the recovery of diploid hybrids by 2x × 2x crosses for obtaining grapefruit-like varieties of citrus with lower furanocoumarin and higher flavonoid contents. [ABSTRACT FROM AUTHOR]

Red-fleshed pummelo (Citrus grandis), a mutant of 'Guanxi', is an important economic plant rich in carotenoids. The transcriptome of 'Guanxi' pummelo was compared with red-fleshed pummelo, with the aim of identifying the key genes responsible for red flesh through RNA sequencing. In total, 44.11 and 47.71 Gb clean reads were respectively obtained after filtering in red and white flesh. Altogether 46,425 unigenes, with an average length of 1208 bp, were assembled. Compared with that of white flesh, 3722 genes were up-regulated, whereas 1421 genes appeared down-regulated in the red-fleshed pummelo. A GO analysis assigned 11,983 differentially expressed genes to 53 subcategories, and 3582, 4722 and 3679 differentially expressed genes were involved in biological processes, cellular components and molecular functions, respectively. The mevalonate pathway involved in terpenoid backbone biosynthesis was significantly different between 'Guanxi' pummelo and its red-fleshed mutant, and the differences were closely associated with carotenoid biosynthesis. The expression levels of the carotenoid biosynthetic pathway genes were different between 'Guanxi' pummelo and its red-fleshed mutant, with the upstream genes having higher expression levels in red-fleshed pummelo than in 'Guanxi' pummelo, whereas the downstream gene β-CHX was downregulated. Two bHLH transcription factors (CL4778.Contig1 and CL4778.Contig2) were of the same branch as CubHLH1, regulating carotenoid biosynthesis in Citrus unshiu Marc., and Unigene CL4778.Contig2 had expression differences in two kinds of pummelo, which suggested CL4778.Contig2 should be a candidate gene controlling carotenoid accumulation in red pummelo. The study would be beneficial to identify the major gene regulating the red flesh trait. [ABSTRACT FROM AUTHOR]

Gametophytic self-incompatibility, one of the key characters for production of seedless citrus, is known in pummelo [Citrus maxima (Burm.) Merr.], mandarin (C. reticulata Blanco) and their hybrid cultivars. The allelic variation in Citrus was reported for the self-incompatibility gene (S). However, S allele frequencies and S genotypes of self-incompatible and semi-self-incompatible Citrus cultivars were known only in a few S alleles. In the present study, S3 and S11 alleles were examined with homozygous S1 seedlings (S3S3 and S11S11) of self-incompatible Clementine mandarin (C. clementina hort. ex Tanaka; S3S11) a putative hybrid between self-compatible 'Mediterranean' mandarin (C. deliciosa Ten.) and self-compatible sweet orange [C. sinensis (L.) Osbeck]. One-hundred-forty-six Citrus accessions, including 43 pummelo accessions, were pollinated with each of the homozygous S1 seedlings (S3S3 and S11S11). Pollen tube arrest in the styles of their pollinated pistils indicated that 25 accessions, including Clementine, have an S3 allele each and 18 accessions, including Clementine, have an S11 allele each. Frequency of accessions with S3 allele was 17.7% (25 of 141 accessions examined) and S3 allele frequency was 11.8% (25 of 212 alleles excluding Sf self-compatible allele). Frequency of accessions with S11 allele was 13.2% (18 of 136 accessions examined) and S11 allele frequency was 8.8% (18 of 205 alleles excluding Sf allele). Pummelo accessions have S3 and S11 alleles with the frequencies of 12.2% and 33.3% respectively, suggesting that the two alleles originated from pummelo. Clementine shared S3 allele with two navel oranges, ten common oranges and two tangors, but not with three blood oranges. In the three blood oranges, it was suggested that stylar part mutation (S3sm) resulting in cross compatibility with S3 pollen occurred in their common ancestor. Clementine shared S11 allele with two tangors but did not share it with 'Mediterranean' mandarin. The present result for S3 and S11 alleles in Citrus accessions suggests that the two S alleles expanded their distribution in Citrus plants including sweet orange along with stylar part mutation for S3 allele during long history of cultivation. [ABSTRACT FROM AUTHOR]

The present study was conducted with the aim to characterize different indigenous pummelo genotypes based on 19 quantitative and 9 qualitative traits. Leaf shape, leaf margin shape, leaf apex shape, petiole wing, petiole wing shape, fruit shape, fruit apex shape, fruit axis, fruit surface texture and pulp colour were the main qualitative characters of study. The higher coefficients of variation were determined for petiole area (36.33%), juice quantity (17.38%), leaf area (14.50%) and fruit weight (14.22%). Principal component analysis (PCA) for quantitative traits indicated that six PCA had Eigen-value greater than one. The cumulative variation explained by six components, viz. leaf length, fruit width, leaf length: width ratio, leaf area, petiole area and lamina wing ratio accounted over 86.12 % variability. However, the result of the PCA for qualitative traits showed that three parameters namely leaf shape, leaf margin shape and leaf apex shape among 10 Principal Component Axis (PCA) had Eigen-values greater than one, and accounted for over 70.23% of the total variability. Based on PCA and coefficient of variation, traits like fruit weight, seed content, juice content, leaf and petiole area, leaf length, leaf width and leaf length: width ratio had significant involvement in pummelo diversity, and can be used in differentiating accessions of citrus.

Pummelo (Citrus maxima L.) is a natural, mono-embryonic and a true fruit species of genus Citrus cultivated widely in India. The study aimed at developing in vitro technique for conservation of Citrus maxima germplasm using shoot tip and nodal section as explants. Various concentrations and combination of hormones were used for successful in-vitro conservation. The shoots sprouted within 9-20 days when inoculated on MS medium supplemented with 0.5 mg/l BAP + 0.1 mg/l NAA growth hormones and above 86% germination was obtained with maximum numbers of shoots (8) and nodes (8.67). Highest shoot elongation (82%) was observed in MS medium supplemented with concentration of 0.6 mg/l GA3 in combination with 0.2 mg/l BAP, shoot length ranged between 1.17 to 6.90 cm and the number of nodes was 2.33-8.33 per plantlet. 1/2 MS medium supplemented with 0.5 mg/l BAP +1.0 mg/l NAA along with 2.5 g phytagel showed best result for rooting (78.33%). The regenerated plantlets did not show any detectable morphological variation at genetic level as evidenced by SSR profiles of plantlets. The developed protocol can be successfully employed for large-scale multiplication and conservation of Pummelo germplasm.

Research Background: There is considerable diversity in newly developed pummelo × sweet orange citrus hybrids. Most hybrids showed lower peel thickness and high juice yield but there is a lack of information on fruit quality parameters and molecular characterization. Therefore, the aim of the current study is to determine the content of antioxidants and properties of the fresh juice of 24 new pummelo × sweet orange citrus hybrids ( Citrus maxima [Burm. f.] Osbeck × Citrus sinensis [L.] Osbeck) and the parental genotypes along with molecular characteristics determined using acidity specific markers., Experimental Approach: The correlation and estimate of inheritance of the fruit juice properties: ascorbic acid, total phenol, total flavonoid, total antioxidant, total soluble solid and sugar contents, pH, titratable acidity, along with sensory evaluation was performed. Molecular characterization of these hybrids was carried out using de novo generated acidity specific simple sequence repeat (SSR) markers., Results and Conclusions: The main constituents of the fruit juice of pummelo × sweet orange hybrids were observed in the range of w (ascorbic acid)=40.00-58.13 mg/100 g, total phenols expressed as gallic acid equivalents w (GAE)=40.67-107.33 mg/100 g, total antioxidants expressed as Trolox equivalents b (Trolox)=2.03-5.49 µmol/g, total flavonoids expressed as quercetin equivalents w (QE)=23.67-59.33 mg/100 g, along with other properties: total soluble solids=7.33-11.33 %, w (total sugar)=2.10-5.76 %, w (reducing sugar)=1.69-2.78 %, w (non-reducing sugar)=0.39-3.17 % and titratable acidity 1.00-2.11 %. The above parameters differed significantly in the fruit juice of the evaluated pummelo × sweet orange hybrids. Considering these parameters, the hybrids SCSH 17-9, SCSH 13-13, SCSH 11-15 and SCSH 3-15 had superior antioxidant properties in terms of these parameters. A higher heritability (≥80 %) was also observed for all juice properties. Molecular characterization of pummelo × sweet orange hybrids showed that >50 % of the hybrids were grouped with medium acidity parents. Both molecular and biochemical parameter-based clustering showed that interspecific hybrids exhibit transgressive segregation with increased antioxidants that help alleviate the health problems., Novelty and Scientific Contribution: These newly developed pummelo × sweet orange citrus hybrids are a valuable source of high-quality antioxidants for a healthy diet. The identification of trait markers that enable selection at the seedling stage is of great benefit to citrus breeders, as the characteristic features of a mature tree are not yet visible at the juvenile stage., Competing Interests: CONFLICT OF INTEREST The authors declare that they have no conflict of interest., (Authors.)

The research was conducted in the pummelo growing areas of Thailand. The results showed that the dropped fruits had a statistically smaller fruit size (7.25 cm) than the retained fruit (9.35 cm; P < 0.05) at 4 months after fruit set. Moreover, the dropped fruits had an abnormal fruit shape when compared to the retained fruits. Consideration of fruit and leaf carbohydrate concentrations showed that the retained fruits had statistically higher carbohydrate concentrations (262 mg g−1) than the dropped fruits (203 mg g−1; P < 0.05). Meanwhile, the dropped fruits had statistically lower leaf carbohydrate concentrations (55 mg g−1) than those in the retained fruits (85 mg g−1; P < 0.05). The retained fruits also had statistically higher N, P, and K concentrations (1.6%, 1.1%, and 1.3%, respectively) than the dropped fruits (1.1%, 0.5%, and 1.0%, respectively; P < 0.05). Therefore, the causes of early fruit drop in pummelo could be insufficient carbohydrate and plant nutrients supplied for fruit growth and development. [ABSTRACT FROM AUTHOR]

The effects of fruit thinning on fruit drop, leaf carbohydrates concentration, fruit carbohydrates concentration, leaf nutrient concentration and fruit quality in pummelo cultivar Thong Dee growing in Nakhon Pathom province, Thailand, were studied during January-August 2013. The results showed that 50% fruit thinning by hand at 1 month after fruit set increased percent of fruit retention throughout fruit development. At 2 month after fruit set, 50% fruit thinning gave 62% of fruit retention, which were significantly higher than no thinning (36.60%), whereas, 50% fruit thinning gave 40% of fruit retention at 6 month after fruit set, which significantly higher than no thinning (20.2%). A significant difference in leaf carbohydrate concentration was found in 3-6 month after fruit set. At 3 months after fruit set, 50% fruit thinning gave significantly higher leaf carbohydrate concentration (81.80 mg.g-1) than no thinning (73.56 mg.g-1), whereas, at 6 month after fruit set, 50% fruit thinning gave significantly higher leaf carbohydrate concentration (128.92 mg.g-1) than no thinning (102.90 mg.g-1). Although, 50% fruit thinning gave no effect on peel and pulp dry weight including peel and pulp carbohydrates concentration during fruit development. For plant nutrient analysis, 50% fruit thinning gave significantly higher leaf nitrogen (N), phosphorus (P) and potassium (K) concentration than no thinning during 3-6 month after fruit set. However, 50% fruit thinning had no effect on fruit weight, fruit circumstance, fruit diameter, titratable acidity (TA) and total soluble solid (TSS). It was concluded that 50% fruit thinning increased percent of fruit retention and may have an effect on the accumulation of leaf carbohydrates, leaf N, leaf P and leaf K concentrations in pummelo cultivar Thong Dee.

China is one of the main production areas of pummelo [Citrus grandis (L.) Osbeck.] in the world and has lots of distinctive local cultivars. Systematic research on the detection of phenolics and antioxidant capacity of peels of mature local cultivars pummelo fruits is rare. In the current study, phenolic composition and content in peels (flavedo and albedo) of ten Chinese local pummelo cultivars were determined using Ultraviolet Spectrophotometer and High Performance Liquid Chromatography (HPLC), and their antioxidant capacities were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals, ferric reducing antioxidant power (FRAP), and 2,2′-azino-bis (3-ethylbenzthiazoline-6)-sulfonic acid (ABTS) methods in the current study. The research not only provides data that support making full use of the resources of Chinese local pummelo cultivars, but also lays the theoretical basis for research of pummelo fruit nutrition and health values. The results showed that the total phenolic (TP) content in albedo was significantly higher than that in flavedo; on the contrary, the total flavonoid (TF) content was lower in the albedo than in the flavedo. C. grandis ‘Hongxinyou’ flavedo contained the highest TP contents, C. grandis ‘Liangpingyou 78-8’ flavedo contained the highest TF contents, and C. grandis ‘Guanxi Miyou’ albedo contained the highest TP and TF contents. Naringenin, hesperetin, diosmin, and gallic acid were the predominant phenolics in the flavedo, whereas hesperetin, diosmin, rutin, chlorogenic acid, and gallic acid were the primary phenolics in the albedo. The flavedo of C. grandis ‘Yubei Shatianyou’ and the albedo of C. grandis ‘Dianjiang Baiyou’ had the highest antioxidant potency composite (APC) indexes. Overall, the ‘Yubei Shatianyou’ flavedo and the ‘Dianjiang Baiyou’ albedo are excellent sources of antioxidants and have the greatest potential value for exploitation and utilization.

The citrus industry at present is severely affected by huanglongbing disease (HLB). HLB is caused by the supposed bacterial pathogen “Candidatus Liberibacter asiaticus” and is transmitted by the insect vector, the Asian citrus psyllid, Diaphorina citri Kuwayama. Developing new citrus hybrids to improve HLB management is much needed. In this study, we investigated the metabolomic profiles of three new hybrids produced from the cross of C2-5-12 Pummelo (Citrus maxima (L.) Osbeck) × pollen from Citrus latipes. The hybrids were selected based on leaf morphology and seedling vigor. The selected hybrids exhibited compact and upright tree architecture as seen in C. latipes. Hybrids were verified by simple sequence repeat markers, and were subjected to metabolomic analysis using gas chromatography-mass spectrometry. The volatile organic compounds (VOCs) and polar metabolites profiling also showed that the new hybrids were different from their parents. Interestingly, the levels of stored VOCs in hybrid II were higher than those observed in its parents and other hybrids. The level of most VOCs released by hybrid II was also higher than that released from its parents. Additionally, the preference assay showed that hybrid II was more attractive to D. citri than its parents and other hybrids. The leaf morphology, compact and upright architecture of hybrid II, and its attraction to D. citri suggest that it could be used as a windbreak and trap tree for D. citri (double duty), once its tolerance to HLB disease is confirmed. Our results showed that metabolomic analysis could be successfully used to understand the biochemical mechanisms controlling the interaction of D. citri with its host plants.

Relationship between endogenous hormonal status with pre-harvest fruit drop in pummelo fruitlets cultivar Thong Dee was studied during January 2013-August 2013. The results indicated that the concentration of IAA in normal and dropped fruitlets tended to decrease gradually during fruit development and the concentration of GA3 in normal and dropped fruitlets increased continually throughout the study. However, the concentration of ABA in normal and dropped fruitlets decreased during fruit development. The concentration of IAA and GA3 in normal fruitlets were significantly higher than those in dropped fruitlets during fruit development, whereas the concentration of ABA in normal fruitlets were significantly lower than that in dropped fruitlets. Consideration of plant growth promoters (IAA and GA3 ) and plant growth inhibitor (ABA) ratio showed that IAA/ABA ratio in normal fruitlets at 6 week, 8 week and 10 week after fruit set were 7.54, 7.99 and 9.42, respectively, which were significantly higher than those in dropped fruitlets (1.81, 3.21 and 3.77, respectively). GA3 /ABA ratio in normal fruitlets at 6 week, 8 week and 10 week after fruit set were 4.54, 5.64 and 25.26 respectively which were significantly higher than those in dropped fruitlets (0.65, 3.10 and 6.71, respectively). Moreover, peel and pulp of normal fruitlets had significantly higher IAA concentration (2.63 and 3.85 mgL-1) than dropped fruitlets (2.07 and 1.45 mgL-1). Peel and pulp of normal fruitlets had also significantly higher GA3 concentration (2.52 and 4.20 mgL-1), whereas peel of normal fruitlets had significantly lower ABA concentration (0.39 mgL-1) than dropped fruitlets (5.28 mgL-1) but ABA concentration in pulp could not be detected either in normal or in dropped fruitlets. For the IAA/ABA and GA3 /ABA ratio measurement, it was found that the peel of normal fruitlets had significantly higher IAA/ABA ratio (6.74) than dropped fruitlets (0.39), whereas the peel of normal fruitlets had significantly higher GA3 /ABA ratio (6.46) than dropped fruitlets (0.38). Therefore, it was concluded that dropped pummelo fruitlets had the lower auxin and gibberellin concentration than those in normal pummelo fruitlets but had higher ABA concentration than that in normal pummelo fruitlets. For the plant growth promoter and plant growth inhibitor ratio, the normal pummelo fruitlets had higher IAA/ABA and GA3 /ABA ratios than those in the dropped pummelo fruitlets. Balance of plant hormones is involved in pre-harvest fruit drop in pummelo cultivar Thong Dee.

Thirty-seven chloroplast molecular markers were used to evaluate the genetic diversity and infer the phylogenetic relationship of 24 Algerian Citrus accessions from the Institut Technique de l′Arboriculture Fruitière et de la Vigne germplasm bank. The reliability and consistence of the clustering distribution was further asserted including 5 Spanish accessions from the Instituto Valenciano de Investigaciones Agrarias. The accessions were positioned on a phylogenetic tree of the genus Citrus based on previous analyses of the whole sequence of citrus chloroplast. Algerian accessions clustered into two main clades mostly differentiated by the occurrence of either mandarin or pummelo chloroplast types. All 7 mandarins analyzed were grouped in the same clade while the other cluster subdivided in 4 groups, included 1 lumia, 3 lemons, 2 grapefruits and 11 sweet oranges. Algerian grapefruit accessions were grouped together with the pummelos in a single cluster while all sweet oranges formed an independent and homogenous clade. Interestingly, the lemons studied were clustered in 3 different subclusters while Citrus lumia genotype was isolated in a different group. These results suggest that in contrast to the studied Algerian mandarins or sweet oranges, that share all the same mandarin or sweet orange chloroplast haplotype, the high diversity of current lemon accessions is at least partially correlated with the identity of different pummelo progenitors which evolved from a common ancestor. In addition, the data indicate that Citrus lumia is a new type of citrus chloroplast that appears to be phylogenetically related to the chloroplasts of the pummelo and micrantha group. [ABSTRACT FROM AUTHOR]

Effect of 2,4-D and naphthalene acetic acid (NAA) on fruit drop reduction in pummelo cv. Thong Dee was investigated in the pummelo growing areas of Nakhon Pathom province, Thailand. Five similar sized and aged of pummelo trees were selected to set up the experiment. Ten mature branches with the same size from each pummelo tree were randomly selected around the canopy for 2,4-D (20 and 40 mg L−1), NAA (20 and 40 mg L−1) application and control. All treatments were applied to selected pummelo branches 2 times at full bloom and 2 months after fruit set. The results showed that 20 mg L−1NAA (14.84%) and 40 mg L−1NAA (12.26%) gave significantly higher percent of fruit retention at 6 months after fruit set. However, leaf total nonstructural carbohydrate concentration analysis showed that 40 mg L−12,4-D (104.86 mg g−1) and 20 mg L−12,4-D (96.55 mg g−1) gave significantly higher total nonstructural carbohydrate than those in control (78.44 mg g−1). For fruit quality, 40 mg L−12,4-D and 20 mg L−12,4-D gave the highest peel weight with 435.55 and 358.57 g, respectively, and 40 mg L−12,4-D gave the highest peel thickness with 20.25 mm, while 20 mg L−1NAA gave statistically higher total soluble solid than those in 20 mg L−12,4-D and 40 mg L−12,4-D. Therefore, 20 mg L−1of NAA sprayed 2 times at full bloom and 2 month after fruit set effectively reduced fruit drop and increased percentage of fruit retention in pummelo cv. Thong Dee. [ABSTRACT FROM PUBLISHER]

India is an important diversity center for different types of citrus species including pummelo ( Citrus grandis L. Osbeck). The major objective of the present study was to determine variation in polyphenolic compounds, antioxidant activity, sugars and organic acid in 16 pummelo (red, pink and white flesh) genotypes. Significant differences (p < 0.05) in the fruit quality, polyphenolic content and antioxidant activity were observed among red, pink and white fleshed genotypes. Naringin was the predominant flavonoid compound identified in all genotypes, however, pummelo selection 8 (PS8) and pummelo selection 13 (PS13) were found to be particularly high in naringin. Other phenolics quantified in the juice included, caffeic, epicatechin, benzoic acid, neoeriocitrin, hesperidin, and narirutin. Hierarchical clustering revealed four definite clusters based upon their composition.Thin peeled and red fleshed genotypes, pummelo selection 4 (PS4) and pummelo selection 12 (PS12) with the high concentration of lycopene and phenolics seem to be promising genotypes for breeding elite cultivars. [ABSTRACT FROM AUTHOR]

Parthenocarpy is one of the most essential factors for production of seedless citrus fruits that is a desirable trait for consumers and producers. However, little research has been done on the degree and type of parthenocarpy in citrus, except a few Citrus cultivars. To increase the knowledge about parthenocarpy for cultivation and breeding of seedless citrus, 113 Citrus accessions including pummelo, mandarin and their relatives were investigated. In self-incompatible accessions flower buds just before anthesis were bagged, while in self-compatible accessions they were non-pollinated to examine autonomous parthenocarpy or style-removed three days after pollination to examine stimulative parthenocarpy. Fruit set rate in each treatment in the 113 accessions was recorded one month after anthesis and the mature fruits were harvested to examine their size and seedlessness. There was no clear difference between stimulative and autonomous parthenocarpy in Citrus accessions examined, indicating that fruit set and development in the accessions is due to autonomous parthenocarpy. The parthenocarpic fruit set occurred in 22 of 50 accessions for pummelo, 26 of 32 accessions for pummelo relatives, 3 of 9 accessions for yuzu and relatives, 12 of 21 accessions for mandarin and relatives, and 63 of 113 accessions in total. Of the 63 accessions, matured seedless fruits were harvested form 19 accessions, of which five accessions ‘Shishiyuzu’, ‘Kunenbo’, ‘Okitsu-wase’ and ‘Aoshima’ satsuma mandarins and ‘Kiyomi’ tangor showed very high degree of autonomous parthenocarpy, followed by ‘Kunenbo’ hybrid accessions such as ‘Iyokan’, ‘Hassaku’, ‘Kabosu’ that showed high to moderate degree of autonomous parthenocarpy. Since ‘Kishu’ mandarin (a seed parent of satsuma) and yuzu (a seed parent of ‘Kabosu’) showed very little or no parthenocarpic fruit growth, it was suggested that ‘Kunenbo’ carried parthenocarpic genes to satsuma mandarin and the other ‘Kunenbo’ relatives showing medium to high autonomous parthenocarpy. It is suggested that these and the other accessions determined to have high to moderate degree of parthenocarpy are useful for production of seedless fruits and breeding of seedless Citrus cultivars. [ABSTRACT FROM AUTHOR]

• The whole genome AP2/ERF transcription factor family of pummelo was analyzed by bioinformatics. • Different color parameters, CCI values, Chlorophyll a, chlorophyll b, carotenoid content were observed in fruit exocarp between 'Sanhong' with and without bagging. • The expression levels of several carotenoid metabolism structure genes in pummelo fruit exocarp were measured. • CitERF23, CitERF27 and CitERF32 were proposed as candidate genes related to carotenoid metabolism in pummelo fruit exocarp. Pummelo (Citrus maxima) belong to subfamily Aurantioideae of Rutaceae. In production, 'Sanhongmiyou' exocarp turned out red after bagging but remained yellow green without bagging. Carotenoids were the main color in pummelo exocarp. The AP2/ERF family has been confirmed to be associated with fruit coloring by regulating genes related to carotenoid metabolism in multiple species. To better understand the molecular mechanisms of exocarp coloration and carotenoid accumulation, a total of 126 AP2/ERF transcription factor family members distributed on 9 chromosomes were screened from pummelo genome database and divided into 3 subfamilies including 110 ERF subfamilies, 13 AP2 subfamilies and 3 RAV subfamilies. 26 pairs of genes from the AP2/ERF transcription factor family were colinear. 18 pairs of genes were evolutionarily conserved and functionally different after tandem repetition events. Multi-species collinearity analysis showed close evolutionary relationship between pummelo, Actinidia chinensis and Eriobotrya japonica. Cis-acting elements prediction in the promoter region revealed that members of AP2/ERF family are rich in cis-acting elements which respond to light and plant hormones. Color parameters L*, a*, b* and CCI values were measured. Chlorophyll a,chlorophyll b, carotenoid content in fruit exocarp were determined. Eight ERF genes related to the carotenoid metabolism were screened out and tested by qRT-PCR. The expression pattern of structure genes in carotenoid metabolism were also measured with qRT-PCR. The expression patterns of CitERF23, CitERF27 and CitERF32 appeared correlation with pigment content and color indexes. Meanwhile, CitERF23 showed significant positively correlation with ZDS and CDD4. CitERF27 showed significant positively correlation with CDD1. CitERF32 showed significant positively correlation with PDS. CitERF120 showed significant positively correlation with CDD1. CitERF23, CitERF27 and CitERF32 were proposed as a candidate gene regulating carotenoid metabolism in the AP2/ERF family. [ABSTRACT FROM AUTHOR]

This study investigated the effect of pummelo extract (Citrus maxima) on biochemical, inflammatory, antioxidant and histological changes in NAFLD rats. Forty male Wistar rats divided into four groups were used: (1) control group; (2) fructose associated with high-fat diet - DHF; (3) normal diet + pummelo extract (50 mg/kg); and (4) FHD + pummelo extract. This was administered at dose of 50 mg/kg of the animal's weight, by gavage, for 45 days. Significant improvement in lipid profile, liver and kidney function, inflammation, oxidative stress markers was identified in group 4 compared to group 2. Regarding TNF-α and IL-1β, group 2 showed higher values (respectively 142, 5 ± 0.7 and 560.5 ± 2.7 pg/mg protein) compared to group 4 (respectively 91.4 ± 0.9 and 402.1.4 ± 0.9 pg/mg protein), p < 0.05. Significant increases were found in SOD and CAT activities, respectively 0.10 ± 0.06 and 8.62 ± 1.67 U/mg protein for group 2 and respectively 0.28 ± 0.08 and 21.52 ± 2.28 U/mg of protein for group 4. Decreases in triglycerides, hepatic cholesterol and fat droplets in hepatic tissue were observed in group 4 compared to group 2. Results highlight that pummelo extract may be useful for prevent the development of NAFLD. [Display omitted] [ABSTRACT FROM AUTHOR]

Lignification, which occurs in many horticultural fruit and vegetables, brings about undesirable texture and unfavorable consumer preference. However, this problem has rarely been studied. In this work, three pumelo cultivars cvs “Hongroumiyou” (HR), “Bairoumiyou” (BR), and “Huangroumiyou” (HuR) were stored at 25 °C for 90 days, and juice sacs were sampled to explore the lignin accumulation and its relationship to sucrose and energy depletion were investigated. The results displayed that HuR contained lower sucrose content, lower ATP level, but higher lignin content compared to BR and HR during postharvest storage, indicating that the sequence according to storage resistance on the basis of lignin content is as follows: HuR < BR < HR. Furthermore, sucrose degradation attributed to enhanced activities of neutral invertase (NI), soluble acid invertase (S-AI), cell wall-bound invertase (B-AI), and energy deficit on account of declined ATP level, showed significantly negative correlation with lignin accumulation, suggesting that lignin accumulation occurrence could induce sucrose degradation and energy deficit during postharvest storage. Additionally, higher activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) could accelerate lignin synthesis and resulted in lignin accumulation during postharvest pumelo storage.