scholarly journals Spectral Characteristics of Citrus Black Spot Disease

2016 ◽  
Vol 26 (3) ◽  
pp. 254-260 ◽  
Author(s):  
Alireza Pourreza ◽  
Won Suk Lee ◽  
Mark A. Ritenour ◽  
Pamela Roberts
Keyword(s):  
Spectral Reflectance ◽  
Spectral Characteristics ◽  
Black Spot ◽  
Spectral Signature ◽  
Support Vector ◽  
Svm Classifier ◽  
Wave Band ◽  
Citrus Black Spot ◽  
Phyllosticta Citricarpa ◽  
Significant Yield

Citrus black spot (CBS) is a fungal disease caused by Phyllosticta citricarpa (synonym Guignardia citricarpa). CBS causes fruit lesions and significant yield loss in all citrus (Citrus) species. The most distinguishing CBS symptom is called hard spot, which is a circular lesion with gray tissue at the center surrounded by a black margin. The spectral characteristic of CBS lesions was investigated and compared with the spectral signature of healthy fruit tissue to determine the best distinguishing wave band. Healthy and CBS-affected samples presented similar reflectance below 500 nm and above 900 nm. However, healthy samples reflected more light between 500 and 900 nm, especially within the visible band. Also, spectral reflectance of the same symptomatic lesion was acquired six times over a 2-month period to determine the variation of symptom’s spectral signatures over time after being harvested. A two-sample t test was employed to compare each pair of consecutive repetitions. The results showed that the spectral signature of the CBS lesion did not change significantly over 2 months. The wavelengths between 587 and 589 nm were identified as the distinguishing band to develop a monochrome vision–based sensor for CBS diagnosis. A support vector machine (SVM) classifier was trained using the spectral reflectance data at the selected bands to identify CBS-affected samples in each repetition. The overall CBS detection accuracies varied between 93.3% and 94.6%.

scholarly journals The Effects of Nutrition and Environmental Factors on Conidial Germination and Appressorium Formation of Phyllosticta citricarpa, the Causal Agent of Citrus Black Spot

2019 ◽  
Vol 109 (4) ◽  
pp. 650-658 ◽  
Author(s):  
Nan-Yi Wang ◽  
Megan M. Dewdney
Keyword(s):  
Black Spot ◽  
Nitrogen Sources ◽  
Conidial Germination ◽  
Appressorium Formation ◽  
Potato Dextrose Broth ◽  
Citrus Black Spot ◽  
Fungal Biology ◽  
Biological Studies ◽  
Phyllosticta Citricarpa

Citrus black spot, caused by Phyllosticta citricarpa, has been identified in Florida since 2010 and can reduce fruit yield and marketability. The conditions required for conidial germination have been poorly understood for P. citricarpa, limiting further biological studies. In this study, the effects of citrus juices, concentration, pH, various carbon and nitrogen sources, and environmental conditions were evaluated in vitro. All tested juices, especially ‘Valencia’ (>85%, P < 0.05), favored germination and appressorium formation, whereas sterile water rarely stimulated germination (<1%). The ‘Valencia’ juice effect was concentration and pH dependent, and the maximum rate was reached in 1.5% juice with pH of 3.4. Most carbon, nitrogen, or complex sources did not favor germination or appressorium formation, with the exception of potato dextrose broth. An incubation period of 18 to 24 h at 24°C was required for peak germination and appressorium formation. The further analysis of critical juice components using synthetic citrus juice revealed that sugars, salts, citric acid, and thiamine were most important for germination and appressorium formation (>80%, P > 0.05). These results provide a better understanding of fungal biology of P. citricarpa and a robust and convenient system for further applications such as screening for efficacious fungicides.

scholarly journals Pathogenicity of Phyllosticta citricarpa Ascospores on Citrus spp.

Plant Disease ◽  
2018 ◽  
Vol 102 (7) ◽  
pp. 1386-1393 ◽  
Author(s):  
Nga T. Tran ◽  
Andrew K. Miles ◽  
Malcolm W. Smith ◽  
Ralf G. Dietzgen ◽  
André Drenth
Keyword(s):  
Potential Model ◽  
Black Spot ◽  
Future Studies ◽  
Citrus Black Spot ◽  
Phyllosticta Citricarpa ◽  
Sexual State ◽  
Epidemic Development ◽  
The Impact ◽  
Troyer Citrange

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.

scholarly journals Effects of Location and Season on Seaweed Spectral Signatures

2021 ◽  
Vol 9 ◽  
Author(s):  
Sadhvi Selvaraj ◽  
Bradley S. Case ◽  
W. Lindsey White
Keyword(s):  
Remote Sensing ◽  
Plant Species ◽  
Spectral Reflectance ◽  
Spectral Characteristics ◽  
Plant Diseases ◽  
Spectral Signature ◽  
Seasonal Effect ◽  
Spectral Variation ◽  
Seaweed Species ◽  
The Impact

Remote sensing is an effective tool for applications such as discriminating plant species, detecting plant diseases or drought, and mapping aquatic vegetation such as seagrasses and seaweeds. Each plant species has a unique spectral reflectance which can be used with remote sensing to map them. However, variations in season, illumination, phenological stages, turbidity or location may affect the spectral reflectance. The aim of this study is to understand the spatial and seasonal effect on two commonly found New Zealand native seaweed species, Ecklonia radiata (C. Agardh) J. Agardh. and Carpophyllum maschalocarpum (Turner) Grev. We collected hyperspectral data (using ASD Handheld2 Field spectrometer with wavelength range 325–1,075 nm) of the seaweed species from four locations across four seasons and used mixed effects modelling to determine the model that best described the spectral data of each seaweed species. The results showed some seasonal pattern across the four locations. In general, summer has an effect on both the species in all four locations; likely due to the higher rates of photosynthesis. However, location did not effect the spectral signature of either species in winter. This study shows the potential for analysis of other micro-and macro-environment factors of different species and provides an understanding of the degree of natural spectral variation in seaweeds enabling further assessment of the impact of anthropogenic activities and changing environment on their spectral characteristics and health. It also identifies a general trend for best season to collect data for better classification accuracy across larger areas.

scholarly journals Inoculum Dynamics and Infection of Citrus Fruit by Phyllosticta citricarpa

2020 ◽  
Vol 110 (10) ◽  
pp. 1680-1692
Author(s):  
Nga T. Tran ◽  
Andrew K. Miles ◽  
Ralf G. Dietzgen ◽  
Timothy A. Shuey ◽  
Stephen R. Mudge ◽  
...  
Keyword(s):  
Leaf Litter ◽  
Disease Incidence ◽  
Citrus Fruit ◽  
Black Spot ◽  
Summer Rainfall ◽  
Tree Canopy ◽  
Economic Losses ◽  
Citrus Black Spot ◽  
Spore Trapping ◽  
Phyllosticta Citricarpa

Citrus black spot, caused by Phyllosticta citricarpa, is characterized by fruit blemishes and premature fruit drop, resulting in significant economic losses in summer rainfall areas. The pathogen forms both conidia and ascospores during its life cycle. However, the occurrence of these spores and their contributions to infection of fruit in field conditions are not well understood. Our research using direct leaf litter monitoring and volumetric spore trapping in Queensland orchards revealed that pseudothecia and ascospores in leaf litter as well as trapped ascospores had low abundance, while pycnidia and conidia were highly abundant. Both P. citricarpa and endophytic Phyllosticta spp. were identified, with P. citricarpa being dominant. In replicated field trials, we determined that infection of Imperial mandarin fruit by P. citricarpa occurred from fruit set until week 20 of fruit development, with the key infection events taking place between weeks 4 and 16 in Queensland subtropical conditions. These results demonstrate that protecting fruit during weeks 4 to 16 significantly reduced P. citricarpa infection. We found no significant correlation between the disease incidence in fruit and P. citricarpa conidial abundance in leaf litter or ascospore abundance measured by volumetric spore trapping. Therefore, it is suggested that inoculum sources in the tree canopy other than those detected by spore trapping and direct leaf litter monitoring may play a major role in the epidemiology of citrus black spot. Improved knowledge regarding epidemiology of P. citricarpa and an understanding of propagules causing infection may aid in development of more effective disease management strategies.

scholarly journals ANALYSIS OF COLOR AND SPECTRAL CHARACTERISTICS OF HEN EGG YOLKS FROM DIFFERENT MANUFACTURERS

2019 ◽  
Vol 7 (2) ◽  
pp. 103-122
Author(s):  
Mariya Georgieva-Nikolova ◽  
Atanas Genchev ◽  
Zlatin Zlatev
Keyword(s):  
Spectral Characteristics ◽  
Visible Spectrum ◽  
Egg Yolk ◽  
Classification Error ◽  
Support Vector ◽  
Svm Classifier ◽  
Spectral Processing ◽  
General Classification ◽  
Egg Yolks ◽  
Hen Egg

In the present work an analysis of the separability of hen egg yolks from different manufacturers is made using image and spectral processing and analysis techniques. Apparent properties of three types of egg yolks were determined and a comparative analysis of these properties was made. Discriminant and SVM (Support vector machines) classifiers were used for classification. A general classification error with lower values ​​is obtained with the b (Lab) color component. In the studies of the spectral characteristics of egg yolks from different manufacturers, the highest accuracy of separation of the target areas is obtained with the kernel SVM classifier combined with the kernel variant of the principal components. When using this classifier, general classification errors of up to 1% were obtained. The results confirm the hitherto known research in this area because the major part of the chicken egg yolk properties studied are visible properties that can be analyzed in the visible spectrum of the reflected light.

scholarly journals COPPER OXYCHLORIDE APPLIED ALONE TO CONTROL CITRUS BLACK SPOT

2019 ◽  
Vol 32 (3) ◽  
pp. 616-624
Author(s):  
ANTONIO EDUARDO FONSECA ◽  
ANTONIO DE GOES ◽  
FERNANDA DIAS PEREIRA
Keyword(s):  
Control Measure ◽  
Block Design ◽  
Black Spot ◽  
Additional Treatment ◽  
Copper Oxychloride ◽  
Concentrated Suspension ◽  
Citrus Black Spot ◽  
Progress Curve ◽  
Randomized Block Design ◽  
Phyllosticta Citricarpa

ABSTRACT Citrus black spot (CBS) is a disease caused by the Phyllosticta citricarpa fungus that causes lesions in fruits and, in more severe stages, fruit drops. The use of systemic fungicides is the main control measure for CBS; however, an alternative control measure is the use of cupric fungicides applied alone with short intervals. Therefore, the objective of the present work was to evaluate the effect of applications of copper oxychloride at different rates on the control of CBS. The experiment was conducted in Bebedouro, SP, Brazil, in the 2014/2015 crop season, in a randomized block design, using a Citrus sinensis variety (Valencia). The treatments consisted of copper rates (zero - control; 31, 24.5, 18.5, 12.2, and 9.1 mg of metal copper per cubic meter of canopy) using copper oxychloride (concentrated suspension - CS; 588 g L-1 of copper oxychloride or 350 g L-1 of metal copper), and an additional treatment with application of a cupric fungicide (cuprous oxide) and a strobilurin fungicide. The applications were carried out with 14-day intervals, starting when 2/3 of the petals of the plant's flowers were fallen, totaling 14 applications. The incidence and severity of CBS were evaluated five times with 30-day intervals up to mid-November, when the fruits were harvested. The data were used to calculate the area under the disease progress curve (AUDPC). Applications of copper oxychloride CS at rates of 31 and 24.5 mg m-3 with 14-day intervals are efficient for the control of CBS, with similar efficiency to the farm standard treatment.

scholarly journals The Effects of Postharvest Treatments and Sunlight Exposure on the Reproductive Capability and Viability of Phyllosticta citricarpa in Citrus Black Spot Fruit Lesions

Plants ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 1813
Author(s):  
Providence Moyo ◽  
Paul H. Fourie ◽  
Siyethemba L. Masikane ◽  
Régis de Oliveira Fialho ◽  
Lindokuhle C. Mamba ◽  
...  
Keyword(s):  
Cold Storage ◽  
Black Spot ◽  
Fruit Peel ◽  
Citrus Black Spot ◽  
Citrus Pulp ◽  
Spore Release ◽  
Postharvest Treatments ◽  
Phyllosticta Citricarpa ◽  
Reproductive Capability ◽  
Wax Coating

Citrus black spot (CBS) is caused by Phyllosticta citricarpa, which is classified as a quarantine organism in certain countries whose concerns are that CBS-infected fruit may be a pathway for introduction of the pathogen. This study evaluated the reproductive capability and viability of P. citricarpa under simulated conditions in which the whole fruit, peel segments, or citrus pulp with CBS lesions were discarded. Naturally infected ‘Midknight’ Valencia orange and ‘Eureka’ lemon fruit, either treated using standard postharvest sanitation, fungicide, and wax coating treatments or untreated, were placed into cold storage for 5 weeks (oranges at 4 °C and lemons at 7 °C). Thereafter, treated and untreated fruit were incubated for a further 2 weeks at conditions conducive for CBS symptom expression and formation of pycnidia. The ability of pycnidia to secrete viable pycnidiospores after whole fruit and peel segments or peel pieces from citrus pulp were exposed to sunlight at warm temperatures (±28 °C) and ±75% relative humidity levels was then investigated. The combination of postharvest treatments and cold storage effectively controlled CBS latent infections (>83.6% control) and pycnidium formation (<1.4% of lesions formed pycnidia), and the wax coating completely inhibited pycnidiospore release in fruit and peel segments. Pycnidiospores were secreted only from lesions on untreated fruit and peel segments and at low levels (4.3–8.6%) from peel pieces from pulped treated fruit. However, spore release rapidly declined when exposed to sunlight conditions (1.4% and 0% after 2 and 3 days, respectively). The generally poor reproductive ability and viability of CBS fruit lesions on harvested fruit, particularly when exposed to sunlight conditions, supports the conclusion that citrus fruit without leaves is not an epidemiologically significant pathway for the entry, establishment, and spread of P. citricarpa.

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