Murcott Tangor Research Articles

Physiological and Growth Responses of W. Murcott Tangor Grafted on Four Rootstocks under Water Restriction

Citrus orchards in semi-arid regions are increasingly exposed to drought conditions due to climate change. This study compared the physiological and growth responses of ‘W. Murcott’ tangor (WM) grafted onto Citrus macrophylla (M), Swingle citrumelo (SC), C-35 citrange (C35), or bitter citrandarin (C22) rootstock subjected to two irrigation treatments: daily irrigation to replace 100% of the water lost daily by evapotranspiration (ET; control treatment) or daily irrigation to replace 75% of the water lost daily by ET (water deficit treatment). For trees in each treatment, leaf gas exchange, relative chlorophyll content, chlorophyll fluorescence, midday stem water potential, trunk cross-sectional area, and shoot length were measured 46 days after treatments were initiated. The results showed that WM on SC or C22 rootstock exhibited isohydric behavior, where decreased stomatal conductance limited transpiration in the water deficit treatment. WM on M rootstock exhibited an anisohydric response in the water deficit treatment, where there was no stomatal control of water loss by transpiration. Among the rootstocks tested for WM, the most tolerant to soil water deficit was SC, whereas trees on M rootstock were the most negatively affected by soil water deficit.

Reaction of Mandarins to the Alternaria Brown Spot and Huanglongbing: Identification of Potential Varieties for These Diseases to Be Managed in the Field

Mandarins occupy the third group among citrus produced in Brazil. Primarily aimed at the fresh fruit market, commercial orchards have suffered significant production losses due to the high incidence of diseases, such as the alternaria brown spot (ABS) and huanglongbing (HLB). The fact that 80% of the orchards are composed of two varieties, Ponkan mandarin and Murcott tangor, which are highly susceptible to both diseases, demands intensive chemical control of the diseases in the field, which has resulted in a significant increase in production costs and a negative environmental impact. A total of one hundred and seventy-three mandarin accessions, including several species and hybrids belonging to the Collections of the Instituto Agronômico de Campinas (IAC), were evaluated in the field in an endemic location for the diseases. Evaluations of the incidence and severity of the diseases showed a range of genotypes tolerant to ABS that could replace the current commercial varieties, mainly within the clementine and willow leaf mandarin groups. Although, with differences in incidence and susceptibility to HLB, there are no tolerant varieties to this disease, which significantly impacts the loss of fruit quality.

Microbial natural bioactive formulations in citrus development

Efficient Microorganisms (EM) are commonly used in organic crops; however, there are no studies on their effects on the production of citrus seedlings. The work aimed to evaluate the impact of applying the inoculants Native Efficient Microorganisms (NEM) and the commercial product EM1® in forming the seedling of the rootstock Poncirus trifoliata (L.) Raf and in the development of young plants of Sweet Orange “Valência” (Citrus sinensis (L.) Osbeck) and Murcott tangor (Citrus sinensis x Citrus reticulata Blanco). The inoculant based on efficient microorganisms from the homemade technology of capture and multiplication, native efficient microorganisms (NEM), showed greater microbial diversity when compared to the commercial product EM1®. The results obtained from the dry mass analysis of the Valência orange and Murcott tangor plants indicate that positive effects resulting from the use of EM1® and NEM inoculums can be obtained by cultivating the respective crops in a system with oat straw cover. It was observed that the use of efficient microorganisms, as microbial natural bioactive formulation, has potential use in citrus and that farmers with fewer resources will be able to produce the microorganisms on their properties.

Effect of some postharvest treatments with edible coating materials on storability and quality of Murcott Tangor fruits during cold storage.

Effect of some postharvest treatments with edible coating materials on storability and quality of Murcott Tangor fruits during cold storage.

Disease Resistant Citrus Breeding Using Newly Developed High Resolution Melting and CAPS Protocols for Alternaria Brown Spot Marker Assisted Selection

Alternaria alternata is a fungus that causes a serious disease in susceptible genotypes of citrus, particularly in mandarins. The Alternaria citri toxin (ACT) produced by the pathogen induces necrotic lesions on young leaves and fruits, defoliation and fruit drop. Here, we describe two methods of marker-assisted selection (MAS) that could be used for the early identification of Alternaria brown spot (ABS)-resistant mandarin hybrids. The first method is based on a nested PCR coupled to high resolution melting (HRM) analysis at the SNP08 locus, which is located at 0.4 cM from the ABS resistance locus, and was previously indicated as the most suitable for the selection of ABS-resistant hybrids. The method was validated on 41 mandarin hybrids of the CREA germplasm collection, and on 862 progenies generated from five crosses involving different susceptible parents. Four out of five populations showed Mendelian segregation at the analyzed locus, while a population involving Murcott tangor as male parent showed distorted segregation toward the susceptible hybrids. The second method is based on a cleaved amplified polymorphic sequences (CAPS) marker that was developed using the same primers as the nested PCR at the SNP08 locus, coupled with BccI restriction enzyme digestion. To verify the reliability of the two genotyping methods, in vitro leaf phenotyping was carried out by inoculating A. alternata spores onto young leaves of 101 hybrids, randomly chosen among the susceptible and resistant progenies. The phenotyping confirmed the SNP08 genotyping results, so the proposed method of selection based on HRM or CAPS genotyping could be routinely used as an alternative to KBioscience competitive allele specific polymerase chain reaction (KASPar) single nucleotide polymorphism (SNP) genotyping system to improve citrus breeding programs. While the study confirmed that the SNP08 marker is a reliable tool for MAS of new citrus hybrids with different genetic backgrounds, it also identified a small group of genotypes where the resistance mechanism requires further investigation.

Winter pruning: option for management against alternaria brown spot (Alteraria alternata f. sp. citri) in Honey Murcott tangor [Citrus reticulata Blanco x C. sinensis (L.) Osbeck

Alternaria brown spot (ABS), caused by Alternaria alternata f. sp. citri, is the main fungal disease plaguing tangerines. The main symptoms are falling leaf and fruit, resulting in the loss of production and quality. The initial symptoms in leaves are characterized by small brown or black spots, surrounded, or not, by yellowish halos. In the fruit, dark cortical patches appear that can easily break. In this study, the winter pruning of the plants was investigated to complementary control of ABS. The experiment was conducted in 10-year-old Honey Murcott tangor plants, where two treatments were applied: pruning in winter and no pruning, using a randomized block design with ten replicates. The treatment of winter pruning was performed before the flowering of the plants (September in Brazil), where the branches were cut close to the trunk, the thicker branches were removed. The chemical control was performed in both treatments. Evaluations of disease severity in fruit were performed using a diagrammatic scale; the disease incidence and area under the disease progress curve (AUDPC) were also calculated. The fruit drop and yield (t ha-1) of the plants were quantified, and the temperature and humidity inside the canopy of the plants were measured. Winter pruning had a positive effect on ABS management since it provided a decrease in incidence, severity, and AUDPC values. Fruit fall was reduced, resulting in greater productivity for Honey Murcott tangor plants. The results confirmed the positive effect of winter pruning on the management of alternaria brown spot.

Essential oil profiling of six new citrus hybrids from Murcott tangor and Pera sweet orange

ABSTRACTThe yield and the composition of the peel essential oils (EO) of six new citrus hybrids obtained from the crosses between Murcott tangor—TM [Citrus reticulata Blanco x Citrus sinensis (L.) Osbeck] and Pera sweet orange—LP [C. Sinensis (L.) Osbeck] was evaluated for the first time. The EO yield of the citrus varied from 0.34% to 0.59%. The hybrids that presented higher EO yield per hectare were TMXLP44 (36 L ha−1) and TMXLP294 (21 L ha−1). The majority compound in all samples was the limonene (>80%). Linalool presented the second highest concentration in the samples, being the sample TMXLP294 the one that presented the highest content of this compound (>13%). The principal components analysis revealed that TMXLP44 is the sample that more differs from the parents, whereas TMXLP372 and TMXLP294 are more similar to their parents Murcott tangor and Pera sweet orange, respectively.

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.

Analysis of Defense-Related Gene Expression in Citrus Hybrids Infected by Xylella fastidiosa

Resistance to Xylella fastidiosa was evaluated in 264 hybrids of crosses between Murcott tangor (Citrus reticulata × Citrus sinensis) and Pera sweet orange (C. sinensis) under field conditions. Uninfected hybrids were grafted with buds collected from Pera sweet orange plants infected with X. fastidiosa, forming a plant with two scions (i.e., hybrid branches and Pera sweet orange branches). From these plants, we chose 10 genotypes with three biological replicates. We evaluated gene expression, bacterial multiplication, and citrus variegated chlorosis (CVC) symptom development in both scions. X. fastidiosa was not detected in most hybrid scions and none showed disease symptoms. In contrast, all Pera sweet orange scions were infected with X. fastidiosa and expressed symptoms of CVC. We quantified the expression of 12 defense-related genes by qPCR comparing resistant to susceptible scions. We suggest that some of these genes are involved in resistance of the hybrids to X. fastidiosa, since their expression was significantly higher in the resistant hybrid scions than in tolerant hybrids and scions originated from CVC symptomatic Pera sweet orange buds. However, we note that these data should be interpreted carefully, as the plant genotypes tested are related but necessarily distinct (hybrids of C. reticulata and C. sinensis, in relation to a C. sinensis control). A principal component analysis revealed a relationship between the expression of these genes and hybrid scions, and between scions that originated from infected buds and the presence of the bacteria and plant symptoms. Multiyear field trials are necessary to develop plant resistance to X. fastidiosa. While the experimental design used here had limitations, it allowed us to identify a set of genes potentially involved in Citrus sp. resistance to this pathogen. Future work on the role of these genes in plant defenses to X. fastidiosa infection is necessary to confirm their importance in the displayed resistance phenotype.

Morphological characterization of leaves at different crown positions of tangerine genotypes

The leaf anatomy has been shown as an important tool to understand the interaction between this organ and its microclimate but this topic is still unclear for citrus plants. The objective of this study was to analyze the leaf structure of Ponkan, Fremont and Thomas tangerine and Murcott tangor. Fully expanded leaves were collected collected, from the 2nd and 3rd nodes of plagiotropic branches facing West, at three crown heights (lower, middle and upper). The leaves were fixed in 70% ethanol and embedded in historesin and sectioned in a semi-automatic microtome. The sections were stained with toluidine blue; images were captured under a light microscope coupled and analyzed to measure leaf tissue thickness. The Fremont tangerine leaves had greater epidermis thickness on the adaxial and abaxial surfaces and secretory cavity diameter as well as a shorter distance between secretory cavities, whereas the Murcott leaves had greater palisade and spongy parenchyma thickness. Thus, Fremont and Murcott are potential varieties for xeric conditions, as they are able to reduce transpiration and make optimal use of high incident radiation. The microclimates created by plant architecture may affect the leaf anatomy of the Ponkan, Fremont and Thomas and Murcott trees, allowing anatomical plasticity.

Pathogenicity of Phyllosticta citricarpa Ascospores on Citrus spp.

Citrus black spot, caused by Phyllosticta citricarpa, is one of the most important fungal diseases in many citrus-growing regions with hot and humid summers. Ascospores and conidia are known to contribute to epidemic development of the disease. However, pathogenicity testing has never been done for pure ascospores produced from fully characterized P. citricarpa isolates, due to the inability to induce the sexual state in vitro. Recently, an in vitro mating technique was developed to readily produce pure P. citricarpa ascospores for use in host inoculation studies. To test the pathogenicity of P. citricarpa ascospores, we inoculated Troyer citrange leaves and Murcott tangor fruit with ascospores produced in vitro from characterized P. citricarpa isolates. Typical symptoms of citrus black spot occurred. Recovery of P. citricarpa isolates from symptomatic lesions and their characterization using genetic markers enabled us to identify recombinant genotypes among the isolates recovered from ascospore inoculations and, as such, fulfill Koch's postulates for ascospores. We have also identified Troyer citrange seedlings as a potential model system for citrus black spot inoculation studies, because it allows typical symptoms of citrus black spot to be expressed with a much shorter latent period than on fruit. This will facilitate future studies of epidemiological aspects of P. citricarpa ascospores relative to conidia and improve our understanding of the citrus black spot pathosystem. The susceptibility of Troyer citrange seedlings will also facilitate experimenting with disease management methods, aimed at reducing the impact of citrus black spot.

RESISTANCE TO ALTERNARIA BROWN SPOT OF NEW CITRUS HYBRIDS

ABSTRACT Alternaria brown spot (ABS) disease is caused by the fungus of Alternaria alternata f. sp. citri, which causes injury in leaves, branches and fruits of citrus. The action of the pathogen is directly related to the presence of toxin receptors in susceptible genotypes. The objective of this study was to characterize a population of citrus hybrids obtained from controlled crosses between Pêra de Abril sweet orange and the hybrid of Murcott tangor x Pêra sweet orange (TM x LP 163) for response to ABS through the in vitro inoculation of fungal spores in young detached leaves. The fungus was isolated from the lesions of Murcott tangor fruits that exhibited ABS symptoms. Two hundred thirty-five hybrids were evaluated, and 70 (30%) showed different levels of disease symptoms on detached leaves after 72 hours of inoculation with the fungus, and 165 (70%) were asymptomatic. The frequency of segregation observed (165R:70S) and high level of heritability (h2g = 0.91) suggest that few genes may be involved in controlling the inheritance of ABS resistance in citrus.

Diagrammatic scale for assessing foliar symptoms of alternaria brown spot in citrus

Alternaria brown spot (ABS) is the main fungal disease of mandarins. Cause damage to fruits, branches and leaves. For determinations of disease severity in fruit, there is a specific diagrammatic scale, which does not occur for foliar lesions. In order to standardize leaf reviews of ABS in citrus, a diagrammatic scale was developed from the collection of symptomatic Dancy tangerine and Murcott tangor leaves, with ten levels, from zero to 97% of the area damaged by the pathogen. They were tested by five evaluators who analyzed 100 pictures of symptomatic leaves with and without the use of the proposed scale. To validate the scale, precision and accuracy of assessors in rating the images were compared. Results showed that the use of the scale improved the accuracy of the evaluators, with increased accuracy. This shows that the leaf scale can be used to determine the severity of alternaria brown spot in citrus.

Predicting the dielectric behavior of orange and other citrus fruit juices at 915 and 2450 MHz

ABSTRACTDielectric properties (DP: relative permittivity and loss factor) and electrical conductivity are important parameters for evaluating the microwave penetration depth and designing applicators for pasteurization processes. In this context, generalized equations that can predict the DP of a group of food products as a function of their characteristics are useful. The dielectric behaviours of eight citrus fruit juices (Pera, Lima, and Navel oranges, Ponkan tangerine, Murcott tangor, Mediterranean mandarin, Sicilian lemon, and Persian lime) and three Pera/Lima blends (25, 50, 75%) for temperatures between 0 and 90 °C and frequency between 500 and 3000 MHz were studied. The results were correlated with temperature at frequencies of 915 and 2450 MHz. It was possible to quantify the ionic and dipolar contributions. DPs were modelled based on the behaviour of pure water in a semiempirical approach using correction factors, which were correlated with temperature and juice physicochemical characteristics (pH, Brix, conductivity). Polynomial regressions can successfully predict relative permittivity with mean absolute errors of 0.49±0.35% and 0.58±0.48% and the loss factor with errors of 4.1±3.9% and 2.8±2.3% at 915 and 2450 MHz, respectively, for juices with Brix/acid ratio between 1.26 and 29.9.

Increase in final fruit size of tangor (Citrus reticulata × C. sinensis) cv W. Murcott by application of benzyladenine to flowers

Fruit development involves the phenomena of cell division and cell elongation. The process is signalled and regulated by the combined action of hormonal substances such as gibberellins, cytokinins and auxins. Benzyladenine (BA) in the presence of adequate internal auxin concentrations is able to stimulate cell division. When BA is applied to mandarins immediately after flowering, initial fruit development can increase, coinciding with endogenous cytokinin content behaviours. Different BA concentrations were therefore applied through immersion of flowers of tangor cv. W. Murcott during anthesis: 30ppm (BA30); 60ppm (BA60), 90ppm (BA90) and an untreated control. BA effects were first determined on the development of different tissues during early fruit growth stages and final fruit size. In the first growth stage, BA90 led to an increase in the number and size of pericarp cells, with size increases also seen in locules and the central axis. This effect led to larger fruit size at the end of development. There was also an increase in the fruit number retained when treated with BA. No effect was seen on internal quality parameters. The effect of application of different BA concentrations on W. Murcott tangor trees is yet to be determined.

QTL mapping for fruit quality in Citrus using DArTseq markers

BackgroundCitrus breeding programs have many limitations associated with the species biology and physiology, requiring the incorporation of new biotechnological tools to provide new breeding possibilities. Diversity Arrays Technology (DArT) markers, combined with next-generation sequencing, have wide applicability in the construction of high-resolution genetic maps and in quantitative trait locus (QTL) mapping. This study aimed to construct an integrated genetic map using full-sib progeny derived from Murcott tangor and Pera sweet orange and DArTseq™ molecular markers and to perform QTL mapping of twelve fruit quality traits. A controlled Murcott x Pera crossing was conducted at the Citrus Germplasm Repository at the Sylvio Moreira Citrus Centre of the Agronomic Institute (IAC) located in Cordeirópolis, SP, in 1997. In 2012, 278 F1 individuals out of a family of 312 confirmed hybrid individuals were analyzed for fruit traits and genotyped using the DArTseq markers. Using OneMap software to obtain the integrated genetic map, we considered only the DArT loci that showed no segregation deviation. The likelihood ratio and the genomic information from the available Citrus sinensis L. Osbeck genome were used to determine the linkage groups (LGs).ResultsThe resulting integrated map contained 661 markers in 13 LGs, with a genomic coverage of 2,774 cM and a mean density of 0.23 markers/cM. The groups were assigned to the nine Citrus haploid chromosomes; however, some of the chromosomes were represented by two LGs due the lack of information for a single integration, as in cases where markers segregated in a 3:1 fashion. A total of 19 QTLs were identified through composite interval mapping (CIM) of the 12 analyzed fruit characteristics: fruit diameter (cm), height (cm), height/diameter ratio, weight (g), rind thickness (cm), segments per fruit, total soluble solids (TSS, %), total titratable acidity (TTA, %), juice content (%), number of seeds, TSS/TTA ratio and number of fruits per box. The genomic sequence (pseudochromosomes) of C. sinensis was compared to the genetic map, and synteny was clearly identified. Further analysis of the map regions with the highest LOD scores enabled the identification of putative genes that could be associated with the fruit quality characteristics.ConclusionAn integrated linkage map of Murcott tangor and Pera sweet orange using DArTseq™ molecular markers was established and it was useful to perform QTL mapping of twelve fruit quality traits. The next generation sequences data allowed the comparison between the linkage map and the genomic sequence (pseudochromosomes) of C. sinensis and the identification of genes that may be responsible for phenotypic traits in Citrus. The obtained linkage map was used to assign sequences that had not been previously assigned to a position in the reference genome.

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.

Genome wide selection in Citrus breeding

Genome wide selection (GWS) is essential for the genetic improvement of perennial species such as Citrus because of its ability to increase gain per unit time and to enable the efficient selection of characteristics with low heritability. This study assessed GWS efficiency in a population of Citrus and compared it with selection based on phenotypic data. A total of 180 individual trees from a cross between Pera sweet orange (Citrus sinensis Osbeck) and Murcott tangor (Citrus sinensis Osbeck x Citrus reticulata Blanco) were evaluated for 10 characteristics related to fruit quality. The hybrids were genotyped using 5287 DArT_seqTM (diversity arrays technology) molecular markers and their effects on phenotypes were predicted using the random regression - best linear unbiased predictor (rr-BLUP) method. The predictive ability, prediction bias, and accuracy of GWS were estimated to verify its effectiveness for phenotype prediction. The proportion of genetic variance explained by the markers was also computed. The heritability of the traits, as determined by markers, was 16-28%. The predictive ability of these markers ranged from 0.53 to 0.64, and the regression coefficients between predicted and observed phenotypes were close to unity. Over 35% of the genetic variance was accounted for by the markers. Accuracy estimates with GWS were lower than those obtained by phenotypic analysis; however, GWS was superior in terms of genetic gain per unit time. Thus, GWS may be useful for Citrus breeding as it can predict phenotypes early and accurately, and reduce the length of the selection cycle. This study demonstrates the feasibility of genomic selection in Citrus.

Chalcones to control Alternaria alternata in murcott tangor fruits

Alternaria brown spot (ABS), caused by the fungus Alternaria alternata pathotype tangerine, is one of the main phytosanitary problems for mandarin growers. About 15 applications per year of harmful fungicides are required for controlling ABS disease in citrus orchards. As chalcones seem to be less toxic to humans and environment than the commercial fungicides in use, this study initially aimed at synthesizing 137 chalcones through aldolic condensations between benzaldehydes and acetophenones. The resulting chalcones were screened for activity against A. altern ata through a fungal growth assay that was carried out in 96-cell polypropylene plates, using the same concentration to all studied substances. The four active chalcones underwent conidia germination and mycelial growth, which confirmed the antifungal activity of the compounds. These chalcones were then poured onto Murcott tangor fruit that had been inoculated with conidia of the fungus. All four chalcones reduced the ABS progress to values significantly smaller (P≤0.05) than that observed for the control. Statistical calculations showed that the best results were afforded by two compounds, bearing a 2,4,5-trimethoxyphenyl group at position 3 of prop-2-enal and a 3-nitro- or 3-hydroxyphenyl group at position 1 of the aldehyde. Such compounds reduced the incidence of the disease in Murcott tangor fruit to values that did not differ statistically from those obtained with a commercial fungicide.

Positive relationship between citrus leaf miner and alternaria brown spot

Alternaria brown spot, or ABS (Alternaria alternata), is the most prevalent fungal disease of tangerines in the world. Field observations have revealed ABS lesions on leaves wounded by the citrus leaf miner (CLM). Thus, the objective of this study was to assess the relationship between CLM and ABS. Leaves from young Murcott tangor plants and detached leaves from 16 different varieties of tangerines with and without lesions caused by CLM were inoculated with A. alternata. The symptoms of the plants were subsequently quantified by counting the number of lesions, and the lesion area was estimated using a diagrammatic scale. The presence of CLM damage aggravates the severity of Alternaria alternata fungus infections in susceptible tangerine varieties.