Ponkan Mandarin Research Articles

Pre and Post-Harvest Treatments to Improve Ponkan Mandarin Fruits Quality 1. Maintaining Fruit Quality during Cold Storage

Ponkan mandarin (Citrus reticulata, Blanco) occupies a prime position among the mandarin species cultivated in Egypt, owing to its high productivity and early yields as well as fruits have a high nutritive value. Despite its attributes and commercial importance, Ponkan mandarin fruits cannot be sustained for a long period due to its poor shelf life. So, the present study was conducted during 2017 and 2018 seasons on 10 years old trees, grown in clay soil at the experimental farm of Faculty of Agriculture, Kafr El-Sheikh University, Egypt, to evaluate the effect of putrescine at 0, 50 and 100 ppm as pre-harvest treatments individually or combinations with salicylic acid at 0, 200 and 400 ppm as post-harvest treatment on fruit properties during cold storage at 5±1 °C and 90 - 95 % RH for 90 days.The obtained results revealed that pre and postharvest treatments of putrescine and salicylic acid enhanced achievment fruits with acceptable qualities during cold storage period as compared to control. The combination treatment of putrescine pre-harvest spraying at 50 ppm plus salicylic acid post-harvest dipping at 400 ppm (T7) was more effective on fruit quality such as fruit weight loss, decay, firmness, SSC%, acidity, SSC/acid ratio and vitamin C during cold storage. Therefore, putrescine and salicylic acid treatments have capability to avoid post-harvest and storage losses along with enhancing quality of the stored fruits.

Pre and Postharvest Treatments to Improve Ponkan Mandarin Fruit Quality 2. Extending Shelf Life of Fruits under Room Temperature Conditions

The present study was intended to find a treatment that maintains the quality of the Ponkan mandarin fruits (Citrus reticulata, Blanco) and extends the marketing period under the room conditions. So, nine treatments were arranged in a complete randomized design of three replicates to study the effect of pre-harvest application of putrescine at 0 , 50 and 100 ppm and post- harvested application of salicylic acid at 0 , 200 and 400 ppm, alone or in combinations on fruit characteristics of Ponkan mandarin during storage under room temperature conditions. The obtained results revealed that, salicylic acid and putrescine applications reduced the weight loss (%) and fruit decay (%) and maintained fruit quality in terms of fruit firmness, SSC (%), acidity, SSC/acid ratio and vitamin C during storage at room conditions. Moreover, pre-harvest application of putrescine at 50 ppm plus post-harvest dipping of salicylic acid at 200 ppm or 400ppm (T6 and T7) were able to maintain fruits with acceptable qualities and good appearance during storage under room conditions. So, it can be concluded that using 400 ppm salicylic acid as post- harvest application, alone or in combination with 50 ppm putrescine as pre-harvest application is a beneficial treatment to increase the shelf life period of Ponkan mandarin fruits during short term storage.

Polyploidy remodels fruit metabolism by modifying carbon source utilization and metabolic flux in Ponkan mandarin (Citrus reticulata Blanco)

The phenotypic variations that follow polyploidization are expected to improve agricultural productivity and efficiency [1]. However, the effect of polyploidization on plant metabolism has rarely been studied. This study evaluated the metabolic alterations that followed autotetraploidization in the fruit of Ponkan mandarin (C. reticulata Blanco) for three consecutive years and explored the underlying changes to the transcriptome. The autotetraploid (4x) Ponkan fruit had higher levels of total acids, ascorbic acid and total phenolic compounds than the diploid (2x). The primary metabolites especially the organic acids tended to accumulate at higher levels in the 4x fruit. Conversely, two major groups of secondary metabolites (i.e. flavonoids and carotenoids) tended to accumulate at lower levels. The expression levels of citric acid biosynthesis-related genes were unaltered in 4x fruit compared to the 2x fruit. Additionally, genes associated with the transport and utilization of citric acid were significantly down-regulated during ripening, which might induce increases in the levels of citric acid in the 4x fruit. Lower levels of flavonoids and carotenoids in the 4x fruit are potentially associated with decreases in the transport and utilization of citric acid, which is an important metabolite. Citric acid contributes to respiration by serving as an intermediated in the tricarboxylic acid cycle (TCA) and also provides carbon for the production of secondary metabolites. This study demonstrates that polyploidization can influence metabolism in plants.

Satsuma mandarins grafted onto Swingle citrumelo for early season harvest in subtropical conditions in Brazil

ABSTRACT Although Brazil is the sixth producer of mandarins in the world, fresh fruit exports are neglectable, and few cultivars are available for the domestic market. Main harvest season comprises May to November, with Ponkan mandarin and Murcott tangor representing more than 70% of the production. Therefore, there is a need for alternative early season, seedless varieties that should also be preferably resistant to Alternaria brown spot. We investigated the horticultural performance of ten selections of Satsuma mandarin in subtropical conditions in Bebedouro, northern state of Sao Paulo, Brazil. Clausellina, Okitsu, Unshu SRA-529, Saigon SRA-227, Panache SRA-579, Salzara SRA-341, Miyagawa SRA-444, Kowano SRA-167, FCAV-59 and A2 60.0 selections were grafted on Swingle citrumelo and evaluated up to 7 years old. Unshu, Miyagawa and A2 60.0 presented the highest tree size. These three selections, in addition to Okitsu and Kowano mandarins, resulted in higher fruit yield for the five first harvests (mean of 31.3 kg∙tree–1∙year–1). Panache had the smallest yield efficiency. Miyagawa and A2 60.0 selections presented lower alternate fruit bearing in the evaluated period due to their early bearing habit. These same selections had the largest fruits with the earliest maturation; similar to the Okitsu mandarin, but with lower soluble solids and higher juice content. The overall performance of the Satsuma mandarin selections grafted on Swingle citrumelo and drip irrigated was promising under subtropical climate. The Okitsu, Miyagawa and A2 60.0 mandarins were selected because of their highest productive potential and their valuable quality traits for the Brazilian domestic market.

Comparative transcript profiling reveals the mechanism of female sterility associated with seedless Ponkan mandarin (Citrus reticulata Blanco).

Seedlessness is a highly desirable trait in citrus varieties. Sterility is the key determination for seedlessness formation. However, the molecular basis for female sterility in seedless mandarin remains unclear. Thus, a seedless Ponkan mandarin (Citrus reticulata Blanco 'Lipeng No.2'), considered the bud mutation of normal seedy Ponkan, was collected to identify candidate genes involved in seedless variation. Suppression subtractive hybridization (SSH) screened 1091 uniESTs related to seedy and seedless Ponkan (727 singlets and 364 contigs), which mainly governed catalytic activity, transferase activity, and oxygen binding. By using RNA-Seq technology, 106 differentially expressed genes (DEGs) were captured, of which 74 were up-regulated and 32 were down-regulated. Gene Ontology and pathway analysis showed that six DEGs were enriched in the biosynthesis of secondary metabolite, whereas five DEGs were enriched in the signaling of plant hormones. The combined results of SSH and RNA-Seq indicated the importance of amino acid metabolism in seedless Ponkan. Our findings revealed that the mechanism of seedless Ponkan generation may be related to gene regulation, signal cascade, and hormone levels. This study provided a solid foundation for functional gene identification in seedless Ponkan and a good reference for relevant research on molecular mechanisms of female sterility in Ponkan mandarin.

Biological and molecular characterization of citrus tatter leaf virus in Taiwan

Citrus tatter leaf virus (CTLV) causes chlorotic leaves with bud union incompatibility in citrus scion and its current incidence in Taiwan is 65%. However, the burden of infection has long been underestimated due to its common latency, and the serious threat of tatter leaf disease should be investigated and addressed without delay. Here, the biological characteristics and genome sequences of Taiwanese isolates are evaluated. Full‐length sequencing and phylogenetic analysis of three local isolates revealed similarities with isolates from neighbouring countries, indicating their possible origins. Two mild isolates obtained from Liuchen sweet orange (LCd‐NA‐1) and kumquat (Kq‐6‐2‐46) were inoculated on indicator plants and exhibited differences in foliar symptom expression and temperature tolerance compared with foreign isolates causing severe disease. Improved quantitative PCR‐based detection methods using redesigned primer pairs indicated high sensitivity and specificity for both local and foreign isolates. Similar but delayed systemic symptoms were observed when wildtype virus in vitro transcripts generated from a full‐length infectious clone of the Ponkan mandarin isolate (pCTLV‐Pk‐8) were inoculated on Chenopodium quinoa. These symptoms were unevenly distributed and highly concentrated on the inoculated sides of leaves and top leaves. A single codon mutation (U5642C) in the coat protein transcription start site in the pCTLV‐Pk‐8 sequence resulted in defective systemic infection, indicating a role for the coat protein in viral movement. The combination of biological assays, improved detection and infectious clone construction provides comprehensive information and a foundation for citrus virus management and further research.

Ectopic accumulation of linalool confers resistance to Xanthomonas citri subsp. citri in transgenic sweet orange plants.

In order to clarify whether high linalool content in citrus leaves alone induces strong field resistance to citrus canker caused by Xanthomonas citri subsp. citri (Xcc), and to assess whether this trait can be transferred to a citrus type highly sensitive to the bacterium, transgenic 'Hamlin' sweet orange (Citrus sinensis L. Osbeck) plants over-expressing a linalool synthase gene (CuSTS3-1) were generated. Transgenic lines (LIL) with the highest linalool content showed strong resistance to citrus canker when spray inoculated with the bacterium. In LIL plants inoculated by wounding (multiple-needle inoculation), the linalool level was correlated with the repression of the bacterial titer and up-regulation of defense-related genes. The exogenous application of salicylic acid, methyl jasmonate or linalool triggered responses similar to those constitutively induced in LIL plants. The linalool content in Ponkan mandarin leaves was significantly higher than that of leaves from six other representative citrus genotypes with different susceptibilities to Xcc. We propose that linalool-mediated resistance might be unique to citrus tissues accumulating large amounts of volatile organic compounds in oil cells. Linalool might act not only as a direct antibacterial agent, but also as a signal molecule involved in triggering a non-host resistance response against Xcc.

Reação de híbridos de citros à inoculação com Alternaria alternata

RESUMO A mancha marrom de alternária (MMA), causada por Alternaria alternata, que produz uma toxina específica ao hospedeiro (Host Specific Toxin – HST) é uma doença de grande importância nos pomares de tangerinas no mundo. A doença afeta tangerinas, alguns de seus híbridos interespecíficos e pomelos, sendo que no Brasil, as principais variedades plantadas, a tangerina Ponkan e o tangor Murcott, são altamente suscetíveis ao fungo, que também é saprofítico alternativo, se reproduz nos pomares, sendo seus esporos facilmente disseminados pelo vento. Para esse trabalho, foram selecionados híbridos de citros, obtidos por cruzamentos dirigidos, por apresentarem características agronômicas que os tornam potenciais novas variedades de laranjas e tangerinas, tanto para a citricultura industrial, quanto de mesa. Esses híbridos foram avaliados quanto à resposta à MMA por meio da inoculação com A. alternata in vitro e in vivo, uma etapa imprescindível para a liberação de novas variedades. Foram selecionados mais de trinta genótipos resistentes ou que apresentaram poucos sintomas da doença. A seleção de variedades resistentes à doença é de grande importância econômica, pois além de diminuir os custos de produção, aumentados sobremaneira com a utilização do controle químico, contribui para a diminuição de inóculo no campo.

Traits Driving Tolerance to Atmospheric Fluoride Pollution in Tree Crops

Increased emissions of fluoride into the atmosphere contribute to reducing the sustainability of agricultural systems worldwide. In order to improve the understanding of the factors behind such phenomenon, varieties of citrus (Citrus spp.), Valencia sweet-orange, Ponkan mandarin, and Lisbon lemon and coffee (Coffea spp.), Obata, Catuai, and Apoata, were treated with fluoride nebulization. The trees were exposed to nebulization for 60 min inside a chamber by using medium (0.04 mol L−1) and high (0.16 mol L−1) doses of fluoridic acid (HF) during three nonconsecutive days in a single week, for a total of 26 days of exposure during the experiment. Sixty days after beginning nebulization, we evaluated leaf gas exchange, (ultra)structural organization, tree growth, and fluoride and nutrient concentrations in plant tissue. Photosynthesis and leaf dry mass of citrus and coffee varieties were affected differently by fluoride toxicity, and based on the tolerance index (relative leaf dry mass of control versus leaf dry mass of trees treated with 0.16 mol L−1 HF), the order of sensitivity for the varieties of each species was as follows: for citrus, lemon > mandarin > sweet-orange; and for coffee, Apoata > Catuai > Obata. The ability of the trees to control fluoride absorption most likely explained this contrast in sensitivity among varieties because both photosynthesis and leaf growth were negatively correlated with leaf fluoride concentration. Although disorganization of the thylakoids, degeneration of vascular cells, and disruption of the middle lamella occurred in leaves of all varieties exposed to fluoride, the more severe damage was observed in those with greater sensitivity to the pollutant (i.e., lemon and Apoata coffee). Taken together, these results provided insights into the factors that explain poor performance of citrus and coffee trees under fluoride pollution and also revealed the traits driving the tolerance of these crops such a limiting condition, which included a combination of the following: (i) reduced fluoride absorption, (ii) increased photosynthesis, and (iii) improved maintenance of the ultrastructural organization of leaves.

Digital Gene Expression Analysis of Ponkan Mandarin (Citrus reticulata Blanco) in Response to Asia Citrus Psyllid-Vectored Huanglongbing Infection.

Citrus Huanglongbing (HLB), the most destructive citrus disease, can be transmitted by psyllids and diseased budwoods. Although the final symptoms of the two main HLB transmission ways were similar and hard to distinguish, the host responses might be different. In this study, the global gene changes in leaves of ponkan (Citrus reticulata) mandarin trees following psyllid-transmission of HLB were analyzed at the early symptomatic stage (13 weeks post inoculation, wpi) and late symptomatic stage (26 wpi) using digital gene expression (DGE) profiling. At 13 wpi, 2452 genes were downregulated while only 604 genes were upregulated in HLB infected ponkan leaves but no pathway enrichment was identified. Gene function analysis showed impairment in defense at the early stage of infection. At late stage of 26 wpi, however, differentially expressed genes (DEGs) involved in carbohydrate metabolism, plant defense, hormone signaling, secondary metabolism, transcription regulation were overwhelmingly upregulated, indicating that the defense reactions were eventually activated. The results indicated that HLB bacterial infection significantly influenced ponkan gene expression, and a delayed response of the host to the fast growing bacteria might be responsible for its failure in fighting against the bacteria.

Development and reproduction of Panonychus citri (Prostigmata: Tetranychidae) on different species and varieties of citrus plants.

The species and varieties of citrus plants that are currently grown can favor the population growth of the citrus red mite Panonychus citri (McGregor) (Prostigmata: Tetranychidae) and alter the pest management programs in citrus groves. In this study we evaluated, in the laboratory, the development and reproduction of P. citri and estimated its life table parameters when reared on four varieties of Citrus sinensis (L.) Osbeck (Valencia, Pera, Natal, and Hamlin), one variety of Citrus reticulata Blanco (Ponkan) and one variety of Citrus limon (L.) Burm. (Sicilian). The incubation period and egg viability were not affected by the host plant. However, the development and survival of the immature stage were significantly lower on Hamlin orange than on Valencia, Pera and Natal oranges, Ponkan mandarin and Sicilian lemon. The fecundity and oviposition period of females were lower on Hamlin orange than on the other hosts. Mites reared on Valencia orange and Sicilian lemon had a higher net reproductive rate (R 0 ), intrinsic growth rate (r) and finite rate of increase (λ), and a shorter interval between generations (T) than on Pera, Natal and Hamlin oranges and Ponkan mandarin. On the other hand, mites reared on Hamlin orange had the lowest R 0 , r and λ and the highest T among the hosts. Based on the results obtained we recommend that for Valencia orange and Sicilian lemon, the mite monitoring programs should be more intense to detect the initial infestation of pest, avoiding the damage in plants and the increase in production costs.

Huanglongbing Surveillance Program Actions in the State of Bahia, Brazil

Huanglongbing (HLB) is found in South/Southeastern states of Brazil, but citrus is grown all over the country. For that reason, surveillance procedures should be carried out frequently and contingency plans developed. This study reports the actions of the State Bureau of Agricultural Defense of Bahia (ADAB), for a commercial orchard in Bom Jesus da Lapa (state of Bahia, Northeastern Brazil) suspected of having HLB symptomatic plants. Besides having a Contingency Plan, a protocol that establishes actions to detect and eradicate the disease, ADAB is also a partner of the collaborative network HLB BioMath. In August 2012, an ADAB team inspected 22 hectares of three year old orchards of both Pera sweet orange and Ponkan mandarin. Scouting was performed on total area, and 4.5% of the plants were marked as having HLB-like symptoms. Samples were tested with polymerase chain reaction (PCR) by the Phytopathological Clinic of Sylvio Moreira Citrus Center. The results were negative for HLB bacterium, but a Phytoplasma of 16SrIX Group was found. All symptomatic plants will be eliminated and the surveillance area will be extended. Despite this finding, Bom Jesus da Lapa is 700km away from the most important citrus regions in Bahia: Reconcavo and Litoral Norte. In those regions no suspected plant was ever reported.

Detection and Inoculation of Peanut Witches' Broom Phytoplasma (16SrII‐A) and Periwinkle Leaf Yellowing Phytoplasma (16SrI‐B) in Citrus Cultivars in Taiwan

AbstractTo clarify the phytoplasma associated with Huanglongbing (HLB), a detection survey of phytoplasma in field citrus trees was performed using the standardized nested PCR assay with primer set P1/16S‐Sr and R16F2n/R16R2. The HLB‐diseased citrus trees with typical HLB symptoms showed a high detection of 89.7% (322/359) of HLB‐Las, while a low detection of phytoplasma at 1.1% (4/359) was examined in an HLB‐affected Wentan pummelo (Citrus grandis) tree (1/63) and Tahiti lime (C. latifolia) trees (3/53) that were co‐infected with HLB‐Las. The phytoplasma alone was also detected in a healthy Wentan pummelo tree (1/60) at a low incidence total of 0.3% (1/347). Healthy citrus plants were inoculated with the citrus phytoplasma (WP‐DL) by graft inoculation with phytoplasma‐infected pummelo scions. Positive detections of phytoplasma were monitored only in the Wentan pummelo plant 4 months and 3.5 years after inoculation, and no symptoms developed. The citrus phytoplasma infected and persistently survived in a low titre and at a very uneven distribution in citrus plants. Peanut witches' broom (PnWB) phytoplasma (16SrII‐A) and periwinkle leaf yellowing (PLY) phytoplasma belonging to the aster yellows group (16SrI‐B) maintained in periwinkle plants were inoculated into healthy citrus plants by dodder transmission. The PnWB phytoplasma showed infection through positive detection of the nested PCR assay in citrus plants and persistently survived without symptom expression up to 4 years after inoculation. Positive detections of the phytoplasma were found in a low titre and several incidences in the other inoculated citrus plants including Ponkan mandarin, Liucheng sweet orange, Eureka lemon and Hirami lemon. None of the phytoplasma‐infected citrus plants developed symptoms. Furthermore, artificial inoculation of PLY phytoplasma (16SrI‐B) into the healthy citrus plants demonstrated no infection. The citrus symptomless phytoplasma was identified to belong to the PnWB phytoplasma group (16SrII‐A).

Cochin China atalantia (Atalantia citroides) as a new alternative host of the bacterium causing citrus Huanglongbing

Through graft inoculation and psyllid transmission experiments, the Cochin China atalantia (Atalantia citroides) was found to be a new alternative host of the fastidious bacterium (Candidatus Liberibacter asiaticus = Las) causing citrus Huanglongbing (HLB). The Las pathogen is commonly transmitted by Asian citrus psyllid (Diaphorina citri) in persistent manner. The Cochin China atalantia plants locally called wild lime (WL) including elliptic leaf (WL-1) and elongated leaf (WL-2) types are growing wildly in Cambodia and Cochin China of Southern Vietnam. The Las pathogen infected Cochin China atalantia plants by graft inoculation and psyllid transmission, and survived persistently. The Las was transmitted from Las-infected Cochin China atalantia plants of two types to healthy citrus plants (Ponkan mandarin) and atalantia plants through psyllid transmission. Therefore, the Cochin China atalantia plants of two types may serve as a new alternative host of Las. Higher titer of Las was detected in the Las-infected WL-1 atalantia plant which developed typical yellow mottling symptom, while lower titer of Las was detected in WL-2 atalantia plant developing mild chlorosis symptom.

Characterization of three linalool synthase genes from Citrus unshiu Marc. and analysis of linalool-mediated resistance against Xanthomonas citri subsp. citri and Penicilium italicum in citrus leaves and fruits

Three cDNA clones from Satsuma mandarin (Citrus unshiu Marc.) were isolated and expressed in Escherichia coli. CuSTS3-1 and CuSTS3-2 encode linalool synthases and CuSTS4 encodes a nerolidol/linalool synthase. Transcripts of CuSTS3-1, CuSTS3-2 and CuSTS4 were abundant in young fruit at 60 days after flowering (DAF), flowers and leaves, respectively. Treatments with Xanthomonas citri subsp. citri (XCC), the causal agent of citrus canker and Penicillium italicum (PI), the cause of post-harvest fruit decay, and wounding up-regulated CuSTS3-1 in fruit and mainly CuSTS4 in leaves. Linalool, citral, geraniol and citronellol showed strong antibacterial and antifungal activities against XCC and PI in vitro, while most other mono-and sesquiterpenes, including limonene and gamma-terpinene, did not. Linalool, used at levels similar to those present in resistant Ponkan mandarin (Citrus reticulata Blanco) leaves, was able to inhibit growth of XCC in vitro. Compared to other five citrus types, linalool accumulated at extraordinarily high levels in Ponkan mandarin leaves and was released at high amounts from their leaves, while it was hardly detectable in the most susceptible species, indicating that linalool biosynthesis and accumulation might be involved in plant defense against bacterial and fungal pathogens and be associated with field resistance to citrus canker.

Identification of differentially expressed microRNAs from a male sterile Ponkan mandarin (Citrus reticulata Blanco) and its fertile wild type by small RNA and degradome sequencing

Male sterility, which could result from abnormal anther development, is a main contributor to seedless fruit production in higher plants, including citrus. MicroRNAs (miRNAs) play important roles in plant development by regulating various biological processes. In this study, by high-throughput sequencing of small RNA libraries constructed from two Ponkan mandarin (Citrus reticulata Blanco) lines, i.e., male fertile and seedy “Egan No. 1” and its male sterile and seedless mutant “Qianyang seedless,” a total of 156 known miRNAs from 32 families and 24 novel miRNAs were identified. Analyses of the expression profiles in sequencing data showed that 71 known miRNAs and 11 novel miRNAs were differentially expressed between the seedy and seedless types. By degradome sequencing, a total of 138 targets were identified for 44 miRNA families, among which 5 targets were experimentally validated by RLM-5′RACE. Consistent with the results in previous studies, target annotation demonstrated that most targets of the known miRNAs were transcription factors. Forty-one targets were also detected to be cleaved by 16 novel miRNAs. Expression profile analyses by qRT-PCR revealed a negative regulation between eight known miRNA and their targets during anther development. Our research provides new information about the miRNA regulatory network during anther development and further advances the study about the mechanism of citrus male sterility.

Rhodosporidium paludigenum induced resistance in Ponkan mandarin against Penicillium digitatum requires ethylene-dependent signaling pathway

This work determined if the ethylene dependent signal pathway was required for antagonist-mediated fruit defense mechanisms through investigation of disease resistance against Penicillium digitatum in Ponkan mandarin induced by 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception, and Rhodosporidium paludigenum. Blocking ethylene perception with 1-MCP resulted in an increase in ACS1, ACS2 and ACO expression, and consequently an increase in ethylene production during mechanical wounding and resistance induction. The expression of the ethylene receptors ETR1, ETR2 and ETR4 as well as ethylene response factor (ERF) were observed with similar responses to yeast and 1-MCP stimuli, with ETR3 mRNA accumulation being the most sensitive to yeast application while ERS1 was the least sensitive. When applied at concentrations greater than 500nLL−1, 1-MCP pre-fumigation significantly reduced the fruit's natural protection and R. paludigenum induced disease resistance to Penicillium decay, indicating that ethylene perception was involved in inducting disease resistance. Moreover, expression of the defensive genes CHI, β-1,3-glucanase, PAL and CIN up-regulated by yeast was inhibited to different degrees by the 1-MCP pre-treatment. This study provides evidence that the biocontrol yeast R. paludigenum increased disease resistance in Ponkan mandarin against P. digitatum infection due to ethylene and signaling pathway dependent mechanisms.

Avaliação do banco de germoplasma de mexericas com relação às características físico-químicas e suscetibilidade à mancha marrom de alternária

A produção de tangerinas alcança expressão econômica em alguns estados brasileiros, principalmente em São Paulo, Paraná, Rio Grande do Sul e Minas Gerais. Nos últimos anos, um interesse crescente pelas mexericas tem sido observado no estado de São Paulo, possivelmente pela inviabilidade econômica de manterem-se pomares das principais variedades comerciais para frutos de mesa, tangerina Ponkan e tangor Murcott, devido à alta suscetibilidade à mancha marrom de alternária (MMA). O objetivo deste trabalho foi caracterizar 33 acessos de mexericas do Banco Ativo de Germoplasma de Citros do Instituto Agronômico de Campinas (BAG Citros IAC), visando selecionar variedades com boas características físico-químicas como massa, altura e largura de frutos, cor da casca, rendimento de suco, acidez, sólidos solúveis e Ratio e resistência à MMA para que possam ser comercializadas em outros períodos do ano, em comparação com a variedade mexerica Rio IAC 194, padrão desse grupo, cuja maturação é de meia-estação. Os resultados demonstraram que cerca de 85% dos acessos de mexerica avaliados em campo e in vitro apresentaram resistência à MMA. Selecionaram-se cinco acessos precoces e 11 mais tardios que a Rio IAC 194 como boas alternativas para a ampliação do período de safra de mexericas no estado de São Paulo.

Use of citral incorporated in postharvest wax of citrus fruit as a botanical fungicide against Penicillium digitatum

The antifungal activity of citral against Penicillium digitatum, the causal agent of citrus green mold, was tested by in vitro and in vivo experiments. In vitro assays showed that the minimum inhibitory concentration and the minimum fungicidal concentration (MFC) were both 4000μLL−1. Results of in vivo tests demonstrated that wax+citral (1× MFC) treatment did not effectively inhibit the growth of P. digitatum in Ponkan mandarin fruit, whereas wax+citral (10× MFC) treatment significantly decreased the incidence of green mold after 6 days of storage at 25±2°C. Wax+citral (10× MFC) treatment remarkably increased the content of vitamin C and antioxidant enzyme activities such as catalase, superoxidase dismutase, and peroxidase but decreased the activities of phenylalanine ammonia lyase, polyphenol oxidase, and malonaldehyde. The treatment had minor effects on the pH, coloration index, and total soluble solids. This study provided theoretical data for the practical application of citral on citrus fruit quality during postharvest storage.

RNA-Seq analysis of Citrus reticulata in the early stages of Xylella fastidiosa infection reveals auxin-related genes as a defense response

BackgroundCitrus variegated chlorosis (CVC), caused by Xylella fastidiosa, is one the most important citrus diseases, and affects all varieties of sweet orange (Citrus sinensis L. Osb). On the other hand, among the Citrus genus there are different sources of resistance against X. fastidiosa. For these species identifying these defense genes could be an important step towards obtaining sweet orange resistant varieties through breeding or genetic engineering. To assess these genes we made use of mandarin (C. reticulata Blanco) that is known to be resistant to CVC and shares agronomical characteristics with sweet orange. Thus, we investigated the gene expression in Ponkan mandarin at one day after infection with X. fastidiosa, using RNA-seq. A set of genes considered key elements in the resistance was used to confirm its regulation in mandarin compared with the susceptible sweet orange.ResultsGene expression analysis of mock inoculated and infected tissues of Ponkan mandarin identified 667 transcripts repressed and 724 significantly induced in the later. Among the induced transcripts, we identified genes encoding proteins similar to Pattern Recognition Receptors. Furthermore, many genes involved in secondary metabolism, biosynthesis and cell wall modification were upregulated as well as in synthesis of abscisic acid, jasmonic acid and auxin.ConclusionsThis work demonstrated that the defense response to the perception of bacteria involves cell wall modification and activation of hormone pathways, which probably lead to the induction of other defense-related genes. We also hypothesized the induction of auxin-related genes indicates that resistant plants initially recognize X. fastidiosa as a necrotrophic pathogen.