Mandarin Hybrids Research Articles

Impact of Kinnow Production on the Socio-economic Conditions of Farmers in the Agra Region

The cultivation of Kinnow, a hybrid mandarin fruit, in the Agra region has significantly impacted the socio-economic conditions of local farmers. This study examines the effects of Kinnow production on farmer livelihoods in 10 selected villages within the Agra district. Data collected from 100 Kinnow-growing farmers revealed that the crop contributes substantially to income generation, improving the financial stability of farmers. Factors such as landholding size, access to credit, and market linkages influence the profitability of Kinnow orchards. Despite challenges like market fluctuations and environmental conditions, the introduction of Kinnow has provided an alternative source of income for farmers in a semi-arid region. Additionally, this study outlines the costs involved in establishing and maintaining Kinnow orchards, highlighting the initial high investments required, followed by a significant return as orchards mature. The findings suggest that Kinnow production is a viable and profitable agricultural enterprise that can contribute to both economic growth and social development in the region.

New insights in the flavor and chemistry of Huanglongbing tolerant citrus hybrids with/without Poncirus trifoliata in their pedigree

IntroductionCitrus hybrids with Poncirus trifoliata L. Raf. introgression have gained interest due to their tolerance to Huanglongbing (HLB), a devastating disease for Florida citrus agriculture. While these hybrids inherit disease tolerance from P. trifoliata, they sometimes also suffer from undesirable off-flavors.MethodsA selection of thirteen genotypes were harvested over the 2020-2021 and 2021-2022 seasons. Their juices were evaluated by a trained sensory panel and were comprehensively analyzed for their chemical makeup, including soluble solids content (SSC), titratable acidity (TA), volatiles, flavonoids and limonoids.Results & discussionOverall, along with the commercial orange cultivars ‘Valencia’ and ‘Hamlin’, the HLB-tolerant Poncirus hybrid ‘US SunDragon,’ and the mandarin hybrids Sugar Belle®, FF-5-51-2, and ‘US Superna’ had positive citrus flavor quality. Esters, some sesquiterpenes, along with flavonoids, eriocitrin and quercetin-3-(3R-glucosylrutinoside), were positively correlated with orange flavor while β-ionone and eucalyptol were highly abundant in the mandarins. The flavonoid linarin, was more abundant in Poncirus hybrids with off-flavors than in the Poncirus hybrid ‘US SunDragon’, having high orange flavor. Two mandarin hybrids, FF-5-6-36 and FTP-6-32-67, were not bitter at harvest, but the juice exhibited delayed bitterness after storage at -20°C, which was associated with significant increases of limonin, nomilin, naringenin, and prunin. Interestingly, during freezer storage, a newly identified flavonoid in citrus, tricin-C-hexoside, increased dramatically across all of the genotypes. The identification of disease-tolerant hybrids with satisfactory flavor quality at juicing as well as after storage where delayed bitterness may develop, has great significance for future breeding efforts for fresh fruit or for use in stand-alone juice/juice blends.

Widely Targeted Metabolomic Analysis Provides New Insights into the Effect of Rootstocks on Citrus Fruit Quality.

The use of different rootstocks has a significant effect on the content of flavor components and overall fruit quality. However, little information is available about the metabolic basis of the nutritional value of citrus plants. In this study, UPLC-MS/MS (ultra-performance liquid chromatography-tandem mass spectrometry) was performed to analyze the metabolites of three late-maturing hybrid mandarin varieties ('Gold Nugget', 'Tango' and 'Orah') grafted on four rootstocks ('Trifoliate orange', 'Carrizo citrange', 'Red tangerine' and 'Ziyang Xiangcheng'). A total of 1006 metabolites were identified through OPLS-DA (Orthogonal Partial Least Squares-Discriminant Analysis) analysis. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis revealed the most critical pathways among the different pathways associated with genes grafted on the four rootstocks that were differentially activated, including tryptophan metabolism and sphingolipid metabolism in 'Gold Nugget'; tryptophan metabolism, phenylpropanoid biosynthesis and sphingolipid metabolism in 'Tango'; and pantothenate and CoA biosynthesis- and photosynthesis-related biosynthesis in 'Orah'. A considerable difference between the different rootstocks was also observed in the accumulation of lipids, phenolic acids and flavonoids; further analysis revealed that the rootstocks regulated specific metabolites, including deacetylnomylinic acid, sudachinoid A, amoenin evodol, rutaevin, cyclo (phenylalanine-glutamic acid), cyclo (proline-phenylalanine), 2-hydroxyisocaproic acid, and 2-hydroxy-3-phenylpropanoic acid. The results of this study provide a useful foundation for further investigation of rootstock selection for late-maturation hybrid mandarin varieties.

Analytical study to measure the variability in quality factors attenuating the export of Kinnow/Mandarin fruit

The Kinnow (a King–Willow leaf mandarin hybrid) fruit is highly cultivated and produced in Pakistan. The Kinnow fruits collected from different orchard categories in three Tehsils, i.e., Sargodha, Kot Momin and Bhalwal of Sargodha District, from three plant elevations (top, center and bottom), were analyzed for physical (weight, size, uniformity in color, shape, citrus canker, rind blemishes, firmness, peel thickness, peel percentage and seed rate), chemical (total soluble solids, ascorbic acid contents and juice recovery) and sensory characteristics, as well as phytochemical evaluations. The weight of Kinnow fruit collected from the top of the plant in the orchard of Bhalwal ranged from 148.22 to 160.31 gs, whereas in Kot Momin it ranged from 149.62 to 170.96 gs. The highest percentage of fruits having orange color was present in Kot Momin (55–71 %), followed by Bhalwal (54–63 %) and Sargodha (51–54 %) areas. The fruits collected from Kot Momin showed the highest total soluble solids, i.e. 13.64–14.21 °Brix. Kinnow fruits collected from the orchards of Kot Momin Tehsil at the top level presented the highest ascorbic acid contents (38.43–48.25 mg/100 mL), followed by Bhalwal (29.73–40.38 mg/100 mL) and the least were found in Sargodha (21.63–28.58 mg/100 mL). In addition, the radical scavenging activity of fruit juices collected from the orchards of Kot Momin and Bhalwal was high. The results of all the attributes of each evaluation confirmed the wide range of differences between orchard location areas as well as fruit location on the plant. Such kind of conditions may lead to the attenuation of the exportable quality of Kinnow fruits. Due to these conditions, most of the fruits collected from the orchards of Sargodha were not considered as of export quality compared to fruits collected from Kot Momin and Bhalwal.

Postharvest quality and shelf-life of new mandarin hybrids under cold storage conditions

Postharvest quality and shelf-life of new mandarin hybrids under cold storage conditions

Quality and Flavor of ‘Aliza’ Fruit: A Unique Pomelo × Mandarin Hybrid

‘Aliza’ is a new pomelo × mandarin hybrid (Citrus maxima, cv. Red Chandler × Citrus reticulata, cv. Ora) developed by the Israeli citrus breeding program at the Volcani Institute. Here, we aimed to characterize the quality and flavor of ‘Aliza’ fruit as compared to other commercial citrus fruit, specifically pomelo (C. maxima), grapefruit (Citrus paradisi), orange (Citrus sinensis) and mandarin (C. reticulata). ‘Aliza’ fruits have a similar size as grapefruits, but have a thinner peel and a unique yellowish/golden color. ‘Aliza’ fruits are completely seedless and have especially high juice contents. They also have a unique, highly preferred flavor, characterized by high sweetness and moderate bitterness and acidity, with strong citrusy and tropical fruity aromas. Sensory analyses conducted with the aid of a trained panel and an electronic tongue revealed that the flavor of ‘Aliza’ fruits is different from the flavors of other citrus species. Consumer acceptance and preference tests revealed that ‘Aliza’ fruit are highly appreciated and favored. The aroma volatile profile of ‘Aliza’ fruit was somewhat similar to those of pomelo and grapefruit, but very different from those of orange and mandarin. Overall, ‘Aliza’ fruits can be distinguished from other citrus fruits by their unique color, high juice content and exceptional, unique flavor.

Phenotypic and Genetic Variation in Morphophysiological Traits in Huanglongbing-Affected Mandarin Hybrid Populations

Huanglongbing (HLB) caused by 'Candidatus Liberibacter asiaticus' (CLas) is the most costly disease for the global citrus industry. Currently, no effective tools have been found to control HLB. Most commercial citrus varieties are susceptible to HLB, though some citrus hybrid cultivars have reduced sensitivity to the disease. Citrus breeding populations contain a large diversity of germplasm, with thousands of unique genotypes exhibiting a broad range of phenotypes. Understanding phenotypic variation and genetic inheritance in HLB-affected mandarin hybrid populations are crucial for breeding tolerant citrus varieties. In this study, we assessed 448 diverse mandarin hybrids coming from 30 crosses, and 45 additional accessions. For HLB tolerance, we measured HLB severity visual score and CLas titers by qPCR. We also measured seven morphophysiological traits indirectly related to HLB tolerance with leaf area index (LAI), leaf area (LA), leaf mass per area (LMA), photosystem II parameters (Fv/Fo, Fv/Fm), and photochemical performance index (PIabs). By estimating the genetic variation in five half-sib families, we estimated the heritability of phenotypic traits and found a significant genetic effect on HLB visual score and photosynthesis parameters, which indicates opportunities for the genetic improvement of HLB tolerance. In addition, although it is easy to identify infected trees based on HLB symptomatic leaves, visually phenotyping whole trees can be difficult and inconsistent due to the interpersonal subjectivity of characterization. We investigated their relationships and found that LAI was highly correlated with HLB score, with correlation coefficients of r = 0.70 and r = 0.77 for the whole population and five half-sib families, respectively. Photochemical parameters showed significant correlation with HLB severity and responded differentially with the side of the canopy. Our study suggests that LAI and photochemical parameters could be used as a rapid and cost-effective method to evaluate HLB tolerance and inheritance in citrus breeding programs.

Productive performance of ‘Pera’ sweet orange grafted onto 37 rootstocks in tropical cohesive soils under rainfed condition

• Cumulative fruit yield was decisive for identify promising rootstocks to ‘Pera’;. • Rangpur, Volkamer x Rangpur, Maravilha Sunki and Indio induced higher yield to ‘Pera’;. • Florida Sunki x citrange 13–012 and Sunki x Swingle-041 perform similar to Rangpur. • The citrus rootstocks induced no significant change on the fruit's quality. In tropical cohesive soils of Brazil, ‘Rangpur’ lime provide high fruit yield to ‘Pera’ sweet oranges. However, the predominance of a single rootstock puts the citrus industry in this region at risk. To identify promising rootstocks for diversification of ‘Pera’ sweet orange orchard's in the tropical cohesive soils of Brazil, a trial was established with 37 citrus rootstocks on the northeast coast of Brazil. The horticultural performance, fruit yield up to the tenth year, and physic-chemical fruit quality attributes were evaluated. The rootstocks induced changes in the tree size, cumulative fruit yield fresh mass and size of fruit, but had not significant influence on chemical fruit quality. The Hierarchical Cluster Analysis allowed group rootstocks into three classes, in which the accumulated fruit yield was the attribute that most contributed. A group with 15 rootstocks was chosen due to the best productive performance and fruits with 193.75–218.5 g, 57.36–62.65% of juice with 9.85–13.08° brix, which meets the requirement of the Brazilian market. Among these 15, the hybrid of ‘Volkamer’ lemon (VKL) with ‘Rangpur’ lime (RL), ‘Maravilha Sunki’ mandarin, ‘Indio’ citrandarin and the local selection of RL stood out by inducing the highest yield . VKL × RL – 030 produced fruits later, but favored the highest fruit yield at the tenth year. Trees grafted on these four rootstocks and also onto RLCNPMF, TSKC × CTQT1434 – 001, MXWL × LHA – 004, ‘Santa Cruz’ Rangpur, ‘San Diego’ citrandarin,– 004 and trifoliate TRH-208 had greater production regularity across the harvests, although the last three showed lower cumulative yield. The earliest fruit bearing was induced by TSKFL × CTC13 – 012, followed by the ‘Sunki' mandarin hybrids TSKC × CTQT1434 – 001, RL, TSKC x TRFD -007 and TSKC x CTSW-041. It is concluded that the most promising rootstocks for diversification of citrus orchards under rainfed condition on the northeast coast of Brazil are VKL x RL-030, ‘Maravilha Sunki’ , ‘Indio’, TSKFL × CTC13 – 012 and TSKC × CTQT1434 – 001, RLCNPMF – 004, TSKC x TRFD -007, TSKC x CTSW-041 and MXWL × LHA – 004.

Determination of endogenous zeatin/IAA levels in selected fortune mandarin mutants against Alternaria alternata pv. citri

Alternaria brown spot is a serious disease in mandarins and mandarin hybrids. In this particular research, 9 Alterneria tolerant and 2 susceptible mutant individuals obtained from a series of in vitro and in vivo studies were used. Endogenous indole acetic acid (IAA) and zeatin hormone levels of the individuals were noted before and after the Alternaria disease inoculations in order to determine the hormonal variations during the research. It was determined that endogenous zeatin levels decreased after the inoculation compared to its initial levels. The indole acetic acid levels of the individuals increased after inoculation except for some individuals.

Comprehensive analysis of polyphenols from hybrid Mandarin peels by SPE and HPLC-UV

Polyphenol compounds are the most important bioactive components in citrus peels. An efficient clean-up method based on solid-phase extraction with C18 cartridges (SPE-C18) and high-performance liquid chromatography, coupled with ultraviolet detector (HPLC-UV) determination, was set up for the analysis of phenolic composition in ultrasound assisted extraction from hybrid mandarin (Citrus reticulata) peels (Clemenvilla, Nadorcott, Ortanique). The SPE-C18/HPLC-UV method was validated according to linearity (R2 ≥ 0.998), good precision (intra-day and inter-day), relative standard deviations (<5% in most cases), low limits of detection and quantitation, adequate recovery, and low matrix effect. Eight flavonoids and seven phenolic acids were separated and determined in a single chromatographic run. Ultra-high-performance liquid chromatography, coupled with quadrupole-time-of-flight-mass spectrometry (UPLC-qTOF-MS/MS), was used to confirm the polyphenols previously detected. Results showed that hesperidin and narirutin were the most abundant phenolic compounds in the three hybrid mandarin peel extracts. This study describes an affordable, suitable method for identifying and quantifying phenolic compounds in hybrid mandarin peels. The correlation and analysis of the principal components also showed the main differences between the varieties analysed. There were clear differences between Clemenvilla and Nadorcott and Ortanique, due to the significantly lower narirutin concentration (P < 0.05) in the case of Clemenvilla.

Recovering triploid citrus hybrids from 2x × 2x sexual crosses with the aid of embryo rescue and flow cytometry in Turkey.

Turkey is one of the major exporters of mandarins in the Mediterranean region. Seedlessness in citrus, which is one of the most desired fruit quality traits, especially in fresh mandarin export markets, can be obtained via triploidy as in many fruit species. Triploid plants can be recovered by 2x × 2x hybridizations in citrus, as well as 2x × 4x and 4x × 2x crosses. Hence, we aimed to develop local triploid hybrids by using the embryo rescue technique in five crosses using eight different citrus varieties in the present study. Embryos isolated from abortive seeds derived by 135days after pollinations were cultured on modified Murashige and Tucker (MT) medium by adding different levels of GA3 to achieve a high germination rate. A population of 574 plants was developed as a result of embryo rescue. After screening the ploidy levels of this 574-plant population with the aid of flow cytometry, 4 triploids from 'Encore' × 'Murcott', 8 triploids from 'Fortune' ×'Willow leaf', 1 triploid from 'Kiyomi' × 'Murcott', and 1 triploid from 'Ortanique' × 'Murcott' hybridization were recovered. Triploid hybrid plants and related parents were analyzed with SSR markers heterozygotic for parental mandarin varieties. In addition, we evaluated stomatal characteristics of diploid and triploid hybrids obtained from different crosses. Stomatal traits of diploid and triploid hybrids in all crosses significantly differed except the stomata index. Genotyping of triploid plants confirmed using Simple Sequence Repeat (SSR) molecular markers and five SSRs were able to identify three alleles of triploid hybrids. Selected triploid mandarin hybrids have been grafted on several rootstocks for field trials and are in the process of yield and quality performances.

Combined Transcriptome and Metabolome Analyses Reveal Candidate Genes Involved in Tangor (Citrus reticulata × Citrus sinensis) Fruit Development and Quality Formation

Tangor, an important citrus type, is a hybrid of orange and mandarin and possesses their advantageous characteristics. Fruit quality is an important factor limiting the development of the citrus industry and highly depends on fruit development and ripening programs. However, fruit development and quality formation have not been completely explored in mandarin-orange hybrids. We sequenced the metabolome and transcriptome of three mandarin-orange hybrid cultivars at the early fruiting [90 days after full bloom (DAFB)], color change (180 DAFB), and ripening (270 DAFB) stages. Metabolome sequencing was performed to preliminarily identify the accumulation patterns of primary and secondary metabolites related to fruit quality and hormones regulating fruit development. Transcriptome analysis showed that many genes related to primary metabolism, secondary metabolism, cell wall metabolism, phytohormones, and transcriptional regulation were up-regulated in all three cultivars during fruit development and ripening. Additionally, multiple key genes were identified that may play a role in sucrose, citric acid and flavonoid accumulation, cell wall modification, and abscisic acid signaling, which may provide a valuable resource for future research on enhancement of fruit quality of hybrid citrus. Overall, this study provides new insights into the molecular basis of pulp growth and development regulation and fruit quality formation in mandarin-orange hybrids.

Health-beneficial aroma and taste compounds in a newly developed kombucha using a Huanglongbing-tolerant mandarin hybrid.

Huanglongbing (HLB) is a destructive citrus greening disease; no commercially applicable measures exist. 'LB8-9' Sugar Belle® (SB), originally developed for the fresh market, is the most HLB-tolerant cultivar among commercially available varieties. Due to the limited capacity of the fresh fruit market, there is a need to increase the demand for SB juice. Kombucha is a fermented tea beverage with black tea and sugar, and is considered a healthy drink with an increasing market. Therefore, we aim to study the potential of using SB juice in kombucha production. Regular (black tea with no citrus juice added), Hamlin (black tea with Hamlin juice added), and SB kombucha (black tea with SB juice added) were prepared and analyzed to observe the composition of aroma and taste compounds in the kombuchas. Aroma and taste compounds in the kombuchas were analyzed using gas chromatography-mass spectrometry/olfactometry and liquid chromatography-triple quadrupole mass spectrometry, respectively. For aroma compounds, SB kombucha was characterized by high concentrations of terpenes and their derivatives, which have mandarin-like aroma characteristics and health benefits such as antidiabetic and antioxidant effects. For taste compounds, SB kombucha contained higher amount of fructose and organic acids, which have the potential to increase the intensity of sweetness and sourness, and flavonoids. This would support the potential benefits of using SB to make kombucha. This study provides valuable information about the aroma and taste compounds in SB kombucha and its potential health benefits, compared with regular and Hamlin kombucha. PRACTICAL APPLICATION: This experiment provided valuable information on the elevated aroma and taste compounds, their potential health benefits, and the changes of those compounds during kombucha fermentation in 'LB8-9' Sugar Belle® kombucha, compared to regular and Hamlin kombucha. In the absence of an effective cure or therapy for HLB, this can be the first step for developing alternative citrus product to help the citrus industry mitigate the negative impacts from HLB.

Distinguishing citrus varieties based on genetic and compositional analyses.

Simple sequence repeats (SSR) markers and secondary metabolite composition were used in combination to study seven varieties of citrus for the first time. With reference to established accessions of citrus, two of the varieties (Chanh Giay and Ma Nao Pan) were predicted to be Mexican key limes, while three were mandarin hybrids (Nagpur, Pontianak and Dalandan) and the remaining two (Qicheng and Mosambi) were related to the sweet orange. Notably, Dalandan was genetically more like a mandarin despite often referred to as an orange locally, whereas Mosambi was more likely to be a sweet orange hybrid although it has also been called a sweet lime due to its green peel and small size. Several key secondary metabolites such as polymethoxyflavones (sinensetin, tangeretin etc.), furanocoumarins (bergapten, citropten etc.) and volatiles (citronellol, α-sinensal etc.) were identified to be potential biomarkers for separation of citrus species. However, despite having similar genetic profiles, variations in the volatile profile of the two limes were observed; similarly, there were differences in the secondary metabolite profiles of the three mandarin hybrids despite having a common ancestral parent, highlighting the usefulness of genetic and compositional analyses in combination for revealing both origins and flavour profiles especially in citrus hybrids. This knowledge would be crucial for variety screening and selection for use in flavour or fragrance creation and application.

Molecular mechanisms of growth and disease resistance in hybrid mandarin ( Siniperca chuatsi ♀ × Siniperca scherzeri ♂) revealed by combined miRNA‐mRNA transcriptome analysis

To improve the yield of hybrid mandarin fish, RNA-seq technology is used to further investigate the growth and disease resistance advantages of hybrid mandarin fish and the associated molecular mechanisms. Cluster analysis of the transcriptomes of the three fish groups Siniperca schezeri (S), Siniperca chuatsi (C) and hybrid mandarin fish (H) shows that the gene expression pattern of H is closer to C. We also found that the metabolic pathways in the body of C are the most active. The glycolysis/gluconeogenesis pathway (ko00010) is most typical. This phenomenon is also observed in H, suggesting that both H and C have the advantage of rapid metabolism. When comparing the different genes, we also found that the immune system of S is more active, as evidenced mainly by the significant activation of the ECM- receptor interaction (ko04512) and the phagosome signalling pathway (ko04145). This suggests that S induces the immune system to respond more rapidly by increasing the sensitivity of molecules related to the processing of environmental information in the body. To better understand the mechanism of disease resistance of H, we analysed the target genes of differentially expressed miRNAs and found that the Toll receptor signalling pathway (ko04620) and related immune pathways were significantly enriched. This suggests that H enhances the defence capability of the immune system by improving the ability to sensing the environment. This study revealed the growth and disease resistance mechanism of Hyb through mRNA and miRNA and provided a theoretical basis for crossbreeding.

Influence of Rootstock on the Leaf Volatile Organic Compounds of Citrus Scion Is More Pronounced after the Infestation with Diaphorina citri.

Nowadays, citrus greening or Huanglongbing is considered the most destructive disease in the citrus industry worldwide. In the Americas and Asia, the disease is caused by the putative pathogen, ‘Candidatus Liberibacter asiaticus’ and transmitted by the psyllid vector, Diaphorina citri. It has been shown that volatile organic compounds (VOC) that are released from citrus leaves attract the psyllid vector. Herein, we tested whether the rootstock influenced the stored VOC profile in the scion leaves and if these influences were altered after infestation with D. citri. The VOC profiles of the hexane-extracted leaves of the mandarin hybrid ‘Sugar Belle’ that were grafted on three different rootstocks (C-35, sour orange (SO), and US-897) with and without infestation with D. citri were studied. The GC-MS analysis showed that the scion VOC profiles of the non-infested control trees were similar to each other, and rootstock was not a strong influence. However, after one month of infestation with D. citri, clear differences in the scion VOC profiles appeared that were rootstock dependent. Although the total scion leaf VOC content did not differ between the three rootstocks, the infestation increased scion monoterpenes significantly on US-897 and C-35 rootstock, increased terpene alcohols on US-897 and SO rootstock, and increased sesquiterpenes on SO. Infestation with D. citri significantly reduced fatty acids and fatty acid esters across all of the rootstocks. Therefore, our results suggest that rootstock choice could influence scions with an inducible volatile defense by enhancing the amounts of VOCs that are available for repelling vectors or for signaling to their natural enemies or parasitoids. According to this study, US-897 may be the best choice among the three that were studied herein, due to its diverse and robust VOC defense response to infestation with D. citri.

Screening of ‘King’ Mandarin Hybrids as Tolerant Citrus Rootstocks to Flooding Stress

This work compares the tolerance to long-term anoxia conditions (35 days) of five new citrus ‘King’ mandarin (Citrus nobilis L. Lour) × Poncirus trifoliata ((L.) Raf.) hybrids (named 0501XX) and Carrizo citrange (CC, Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.), the widely used citrus rootstock in Spain. Growth parameters, chlorophyll concentration, gas exchange and fluorescence parameters, water relations in leaves, abscisic acid (ABA) concentration, and PIP1 and PIP2 gene expressions were assessed. With a waterlogging treatment, the root system biomass of most hybrids went down, and the chlorophyll a and b concentrations substantially dropped. The net CO2 assimilation rates (An) and stomatal conductance (gs) lowered significantly due to flooding, and the transpiration rate (E) closely paralleled the changes in gs. The leaf water and osmotic potentials significantly increased in most 0501 hybrids. As a trend, flooding stress lowered the ABA concentration in roots from most hybrids, but increased in the leaves of CC, 05019 and 050110. Under the control treatment (Ct) conditions, most 0501 hybrids showed higher PIP1 and PIP2 expressions than the control rootstock CC, but were impaired due to the flooding conditions in 05019 and 050110. From this study, we conclude that 0501 genotypes develop some adaptive responses in plants against flooding stress such as (1) stomata closure to prevent water loss likely mediated by ABA levels, and (2) enhanced water and osmotic potentials and the downregulation of those genes regulating aquaporin channels to maintain water relations in plants. Although these traits seemed especially relevant in hybrids 050110 and 050125, further experiments must be done to determine their behavior under field conditions, particularly their influence on commercial varieties and their suitability as flooding-tolerant hybrids for replacing CC, one of the main genotypes that is widely used as a citrus rootstock in Spain, under these conditions.

Effect of Canopy Covering on Thermal Insulation and Freezing Tolerence of ‘Shiranui’ Hybrid Mandarin Cultivated in Field During Winter Season

Effect of Canopy Covering on Thermal Insulation and Freezing Tolerence of ‘Shiranui’ Hybrid Mandarin Cultivated in Field During Winter Season

English

Citrus is known as a major fruit due to its high nutritional value and adaptability in tropical and sub-tropical regions. Among diseases, citrus dieback is one of the most threatening diseases in which overall plant growth is reduced. Major causes are Colletotrichum gloeosporioides and citrus nematode (Tylenchulus semipenetrans) with 15-35% losses all over the world. Plant material was established adopting sanitary measures in earthen pots (12-inch diameter). Fresh culture of C. gloeosporioides and T. semipenetrans was prepared for the inoculation by following the standard procedures. In the first set, rootstocks were inoculated with 200mL of water having spore suspension of C. gloeosporioides while in in the second set, inoculation of T. semipenetrans was done by using 45 mL of water suspension having 2000 freshly hatched juveniles per pot, while at the rate of 1 × 107 spores/mL per plant. In the third set, the interaction of C. gloeosporioides and T. semipenetrans was studied by inoculating selected citrus rootstocks by both pathogens. After four months of inoculation, data were recorded on plant disease index (PDI) along with plant growth parameters (root weight, shoot weight, shoot weight, shoot length and number of leaves). Trifoliate orange and cox mandarin hybrid showed resistance against the development of T. semipenetrans while rough lemon, C-35 Citrange and sour orange were found susceptible. There was a significant difference in plant growth parameters between inoculated and healthy plants. Root weight and shoot weight decreased by 8.98g and 11.53g, while root length and shoot length decreased by 7.29cm and 13.5cm respectively as compared to control treatments in most susceptible rootstocks. Per cent Branch Infection (PBI) and per cent Disease Index (PDI) were maximum (71.52, 37) per cent on rough lemon respectively. Results regarding combined inoculation of C. gloeosporioides and T. semipenetrans showed that there was a significant difference in plant growth parameters between inoculated and healthy plants. In rough lemon, Root weight and shoot weight decreased by 13.86 and 20.57g respectively in diseased and healthy plants. Root length and shoot length decreased by 8.37 and 20.04cm respectively as compared to control treatments in most susceptible rootstocks. Overall results depicted that inoculation of both pathogens reduced plant growth more severely as compared to their individual application.

Genetic background of the citrus landrace ‘Huarongdao Zhoupigan’ revealed by simple sequence repeat marker and genomic analyses

The cultivated landrace ‘Huarongdao Zhoupigan’ originated in China, and it has a history of more than a hundred years. It is widely cultivated for its distinctive pericarp, soft juicy pulp, slight bitter taste, and rich flavonoids and vitamin C (17.2 ± 0.08 mg•mL−1). Morphological observation shows that ‘Huarongdao Zhoupigan’ is mandarin-like in leaf shape, fruit flesh, easy peeling and crumpled pericarp, implying this variety may be a hybrid of orange and mandarin. To reveal the genetic background of ‘Huarongdao Zhoupigan’, 21 citrus accessions were evaluated using nuclear and chloroplast SSR markers and whole-genome SNP information. ‘Huarongdao Zhoupigan’ was grouped with mandarins and closely clustered with ‘Yuanjiang Nanju’ in the nuclear SSR analysis and sub-grouped with ‘Goutou’ sour orange, ‘Dahong’ sweet orange and ‘Newhall’ navel orange in the chloroplast SSR analysis. The genomic sequence similarity rate of ‘Huarongdao Zhoupigan’ with mandarin was 36.09%, with mandarin heterozygosity of 46.50%; the rough ratio of the two main parts was nearly 1:1, except for the unknown (19.11%) and pummelo (1.46%) parts. Thus, ‘Huarongdao Zhoupigan’ may be a natural hybrid with sour orange (a sexual hybrid of pummelo and mandarin) as the seed parent and mandarin as the pollen parent.