Sweet Orange Fruit Age and Inoculum Concentration Affect the Expression of Citrus Black Spot Symptoms

Citrus black spot (CBS), caused by Phyllosticta citricarpa, affects different citrus species worldwide. CBS is mainly expressed as false melanose and hard spot symptoms. There is no consensus in the literature about the period when fruit are susceptible to P. citricarpa infection and the length of the CBS incubation period. Therefore, this study aimed to assess the influence of sweet orange variety, fruit age, and inoculum concentration on the incubation period and the expression of different CBS symptoms. Attached fruit of Hamlin, Pera, and Valencia sweet orange at 1.5, 3.0, 5.0, and 7.0 cm diameter were inoculated with suspensions containing 103 and 105 conidia/ml of P. citricarpa. The percent conidial germination was quantified using scanning electron microscopy. The CBS symptoms on fruit were assessed monthly. The four diameters did not significantly affect conidial germination on the inoculated fruit, although CBS incidences were lower when larger fruit were inoculated. Hard spot symptoms on sweet orange fruit did not develop from the false melanose symptoms and vice versa. The incubation periods for false melanose were shorter than those observed for hard spot. False melanose began to appear 44 days after inoculation, but hard spot only formed at 113 days or later. Incubation periods were shorter and incidences of false melanose were higher following inoculation with higher inoculum concentration and smaller fruit diameter. The incubation period of hard spot varied among varieties and fruit diameters. However, there was no relationship between hard spot incidence and variety. This study provides a better understanding of the factors affecting the variation in the CBS incubation period and disease incidence on fruit.

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The Effects of Postharvest Hot Water and Fungicide Treatments on Guignardia citricarpa Growth and the Development of Citrus Black Spot Symptoms on ‘Valencia’ Orange Fruit

HortScience ◽

10.21273/hortsci11187-16 ◽

2016 ◽

Vol 51 (12) ◽

pp. 1555-1560 ◽

Cited By ~ 3

Author(s):

Jiaqi Yan ◽

Megan M. Dewdney ◽

Pamela D. Roberts ◽

Mark A. Ritenour

Keyword(s):

Disease Severity ◽

Mycelial Growth ◽

Disease Incidence ◽

Black Spot ◽

Hot Water ◽

Lesion Development ◽

Guignardia Citricarpa ◽

Citrus Black Spot ◽

Orange Fruit

Citrus black spot (CBS), caused by Guignardia citricarpa, is a fungal disease that was first described in Australia in the 1890s and has since been discovered in Southwest Florida in 2010. The current study evaluated the effects of hot water treatments on mycelial growth of G. citricarpa in vitro and also evaluated postharvest hot-water dips and fungicide treatments on CBS development on ‘Valencia’ oranges. In vitro exposure to 56 °C for 120 seconds, 59 °C for 60 seconds, or 62 °C for 30 seconds suppressed mycelial growth of all three G. citricarpa isolates by >30%. These treatments did not significantly reduce disease incidence or severity of CBS lesion development on whole ‘Valencia’ oranges from CBS-infected trees when the fruit already had visible CBS symptoms before treatment. On asymptomatic fruit, while the treatments did not significantly reduce the incidence of CBS lesion development, fruit dipped in 56 °C water for 120 seconds significantly reduced disease severity after 2 weeks of storage compared with the control. None of the treatments caused peel scalding or fruit quality deterioration. Postharvest application of azoxystrobin, imazalil, or thiabendazole significantly reduced CBS disease severity on fruit that were asymptomatic at harvest, but did not affect disease incidence. These fungicides were not effective on fruit harvested later in the season (April), possibly because most lesion expression had already occurred before harvest, with little left to develop after harvest. On fruit showing CBS symptoms at harvest, postharvest fungicide treatments did not significantly affect disease incidence or severity after storage. Heating the fungicide solutions did not significantly improve fungicide effectiveness. These results demonstrated that fungicide azoxystrobin, imazalil, or thiabendazole could reduce CBS severity, but not incidence, on orange fruit that are still asymptomatic at harvest.

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Citrus black spot severity related to premature fruit drop in sweet orange orchards

Plant Pathology ◽

10.1111/ppa.13461 ◽

2021 ◽

Author(s):

Franklin Jackson Machado ◽

Fabrício Eustáquio Lanza ◽

Marcela Olivetti Ferretti ◽

Régis Oliveira Fialho ◽

Franklin Behlau ◽

...

Keyword(s):

Sweet Orange ◽

Black Spot ◽

Citrus Black Spot ◽

Fruit Drop

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

Phytopathology ◽

10.1094/phyto-10-18-0378-r ◽

2019 ◽

Vol 109 (4) ◽

pp. 650-658 ◽

Cited By ~ 1

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.

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First Report of Guignardia citricarpa Associated with Citrus Black Spot on Sweet Orange (Citrus sinensis) in North America

Plant Disease ◽

10.1094/pdis-01-12-0101-pdn ◽

2012 ◽

Vol 96 (8) ◽

pp. 1225-1225 ◽

Cited By ~ 31

Author(s):

T. S. Schubert ◽

M. M. Dewdney ◽

N. A. Peres ◽

M. E. Palm ◽

A. Jeyaprakash ◽

...

Keyword(s):

North America ◽

Sweet Orange ◽

Black Spot ◽

The United States ◽

Yield Reduction ◽

Rrna Gene ◽

Specific Primers ◽

Oatmeal Agar ◽

First Report ◽

Citrus Black Spot

In March 2010, citrus black spot symptoms were observed on sweet orange trees in a grove near Immokalee, FL. Symptoms observed on fruit included hard spot, cracked spot, and early virulent spot. Hard spot lesions were up to 5 mm, depressed with a chocolate margin and a necrotic, tan center, often with black pycnidia (140 to 200 μm) present. Cracked spot lesions were large (15 mm), dark brown, with diffuse margins and raised cracks. In some cases, hard spots formed in the center of lesions. Early virulent spot lesions were small (up to 7 mm long), bright red, irregular, indented, and often with many pycnidia. In addition, small (2 to 3 mm), elliptical, reddish brown leaf lesions with depressed tan centers were observed on some trees with symptomatic fruit. Chlorotic halos appeared as they aged. Most leaves had single lesions, occasionally up to four per leaf. Tissue pieces from hard spots and early virulent spots were placed aseptically on potato dextrose agar (PDA), oatmeal agar, or carrot agar and incubated with 12 h of light and dark at 24°C. Cultures that grew colonies within a week were discarded. Fourteen single-spore cultures were obtained from the isolates that grew slower than the Guignardia mangiferae reference cultures, although pycnidia formed more rapidly in the G. mangiferae cultures (1). No sexual structures were observed. Cultures on half-PDA were black and cordlike with irregular margins with numerous pycnidia, often bearing white cirrhi after 14 days. Conidia (7.1 to 7.8 × 10.3 to 11.8 μm) were hyaline, aseptate, multiguttulate, ovoid with a flattened base surrounded by a hyaline matrix (0.4 to 0.6 μm) and a hyaline appendage on the rounded apex, corresponding to published descriptions of G. citricarpa (anomorph Phyllosticta citricarpa) (1). A yellow pigment was seen in oatmeal agar surrounding G. citricarpa, but not G. mangiferae colonies as previously reported (1,2). DNA was extracted from lesions and cultures and amplified with species-specific primers (2). DNA was also extracted from G. mangiferae and healthy citrus fruit. The G. citricarpa-specific primers produced a 300-bp band from fruit lesions and pure cultures. G. mangiferae-specific primers produced 290-bp bands with DNA from G. mangiferae cultures. The internally transcribed spacer (ITS) of the rRNA gene, translation-elongation factor (TEF), and actin gene regions were sequenced from G. citricarpa isolates and deposited in GenBank. These sequences had 100% homology with G. citricarpa ITS sequences from South Africa and Brazil, 100% homology with TEF, and 99% homology with actin of a Brazilian isolate. Pathogenicity tests with G. citricarpa were not done because the organism infects immature fruit and has an incubation period of at least 6 months (3). In addition, quarantine restrictions limit work with the organism outside a contained facility. To our knowledge, this is the first report of black spot in North America. The initial infested area was ~57 km2. The disease is of great importance to the Florida citrus industry because it causes serious blemishes and significant yield reduction, especially on the most commonly grown ‘Valencia’ sweet orange. Also, the presence of the disease in Florida may affect market access because G. citricarpa is considered a quarantine pathogen by the United States and internationally. References: (1) R. P. Baayen et al. Phytopathology 92:464, 2002. (2) N. A. Peres et al. Plant Dis. 91:525, 2007 (3) R. F. Reis et al. Fitopath Bras. 31:29, 2006.

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Tree age and cultivar‐oriented use of mineral oil added to fungicide tank mixture for the control of citrus black spot in sweet orange orchards

Pest Management Science ◽

10.1002/ps.6652 ◽

2021 ◽

Author(s):

Geraldo José Silva Júnior ◽

Mario Roberto Moraes ◽

Rafaele Regina Moreira ◽

Franklin Behlau

Keyword(s):

Sweet Orange ◽

Black Spot ◽

Mineral Oil ◽

Tree Age ◽

Citrus Black Spot

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Inoculum Dynamics and Infection of Citrus Fruit by Phyllosticta citricarpa

Phytopathology ◽

10.1094/phyto-02-20-0047-r ◽

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.

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High Humidity and Age-Dependent Fruit Susceptibility Promote Development of Trichothecium Black Spot on Apple

Plant Disease ◽

10.1094/pdis-05-18-0734-re ◽

2019 ◽

Vol 103 (2) ◽

pp. 259-267 ◽

Cited By ~ 4

Author(s):

Pengbo Dai ◽

Xiaofei Liang ◽

Yajing Wang ◽

Mark L. Gleason ◽

Rong Zhang ◽

...

Keyword(s):

Developmental Stages ◽

Disease Incidence ◽

Germination Rate ◽

Black Spot ◽

Apple Fruit ◽

High Humidity ◽

Factors Affecting ◽

Fruit Maturity ◽

Fruit Bagging

Fruit bagging is a widely used orchard practice in China. Trichothecium black spot (TBS) is a disease highly associated with the fruit bagging. In this study, we characterized in vitro factors affecting the causal agent, Trichothecium roseum, and TBS development and infection histology on field-bagged apple fruit in situ. Under in vitro conditions, conidial germination required exogenous nutrients, and the germination rate was significantly promoted by high humidity, a condition mimicking the bag microenvironment. Germ tubes penetrated fruit via natural openings including stomata, lenticels, and surface cracks. To determine the chronology of infection by T. roseum, ‘Fuji’ fruit were inoculated in the field at different developmental stages. The earliest infection occurred 60 days after full bloom (dafb), and disease incidence increased as fruit maturity advanced. At harvest time (165 dafb), lesions on more recently inoculated fruit (105 dafb, 150 dafb) were larger than lesions from fruit inoculated on earlier dates. Histological observation showed that infection of younger fruit elicited stronger host lignification responses restricting lesion development. Taken together, our results support the hypothesis that high humidity in sealed bags and increased susceptibility associated with advancing fruit maturity are key factors promoting T. roseum infection and TBS symptom development on bagged apple fruit.

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Factors Affecting Infection and Disease Development on Olive Leaves Inoculated with Fusicladium oleagineum

Plant Disease ◽

10.1094/pdis-02-11-0126 ◽

2011 ◽

Vol 95 (9) ◽

pp. 1139-1146 ◽

Cited By ~ 19

Author(s):

José R. Viruega ◽

Luis F. Roca ◽

Juan Moral ◽

Antonio Trapero

Keyword(s):

Incubation Period ◽

Disease Severity ◽

Disease Incidence ◽

Leaf Age ◽

Growth Chamber ◽

Factors Affecting ◽

Potted Plants ◽

Inoculum Dose ◽

Detached Leaves ◽

Forecasting System

Infection and development of olive scab disease, caused by Fusicladium oleagineum, were evaluated on detached leaves and potted plants of the susceptible cultivar Picual in growth chambers and a shadehouse. An inoculum dose of 1 × 105 conidia per ml was selected from a range of densities tested, and it was used for all experiments. Infection occurred from 5 to 25°C, and disease severity was the greatest at ~20°C for wetness durations of 12 to 24 h and at ~15°C for longer durations. Based on a generalized form of the Analytis Beta model, the optimum temperature and minimum wetness duration for infection were 15.5°C and 11.9 h. Dry periods ≤78 h immediately after inoculation did not reduce disease incidence but did reduce disease severity. Disease severity was negatively correlated with leaf age. Disease incubation period was positively correlated with leaf age, with a minimum incubation period of 28 days in the youngest leaves. Inoculated plants that were incubated in a growth chamber or in a shadehouse had the same level of infection, but disease severity was lower in plants incubated in the growth chamber because many infections remained latent for 6 months after inoculation. The data in this study will be useful for the development of a forecasting system for olive scab epidemics.

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Influence of Incubation-Period Humidity on the Development of Brown Rot Blossom Blight of Sour Cherry

Phytopathology ◽

10.1094/phyto.1997.87.1.42 ◽

1997 ◽

Vol 87 (1) ◽

pp. 42-49 ◽

Cited By ~ 11

Author(s):

D. C. Koball ◽

W. F. Wilcox ◽

R. C. Seem

Keyword(s):

Water Potential ◽

Incubation Period ◽

Incubation Temperature ◽

Disease Incidence ◽

Sour Cherry ◽

Brown Rot ◽

Causal Mechanism ◽

Ambient Conditions ◽

Incubation Periods ◽

Environment Chamber

When detached sour cherry (Prunus cerasus) blossoms were inoculated with conidia of Monilinia fructicola and subjected to a standard 8-h wetting treatment at 20°C, blossom blight incidence was proportional to relative humidity (RH) when RH was held constant during the subsequent 6-day incubation period (frequency = 1.0 at the maximum RH of 92%; frequency = 0.38 at the minimum RH of 57%). Similarly, when a primary incubation period at 87% RH was followed by a secondary incubation period at 54% RH, blossom blight incidence was proportional to the number of hours at the higher level (frequencies of 0.94, 0.80, and 0.38 with primary incubation periods of 6 days, 36 h, and 12 h, respectively). When intact blossoms on potted trees were exposed to common inoculation and wetting treatments, disease incidence was consistently high on trees that subsequently were incubated in a controlled environment chamber (20°C, 90 to 95% RH) but was extremely variable when trees were incubated under variable ambient conditions. Ambient incubation temperature had little effect on disease incidence 9 days after inoculation, whereas ambient RH had a pronounced effect: the frequency of blighted blossoms was 0.53 to 0.61 when the number of hours at RH >90% was approximately two to six times that at RH <60%, whereas this frequency was only 0.02 to 0.07 when the number of hours at RH >90% was approximately one-third the number at RH <60%. After 48 h at a constant RH of 89 or 57%, the water potential of excised uninoculated blossoms was -1.15 and -1.93 MPa, respectively; however, growth of M. fructicola on osmotically adjusted potato dextrose agar was unaffected by changes in water potential within this range. Thus, although RH during incubation has an important influence on blossom blight development, the causal mechanism remains uncertain.

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Genetic Diversity and Population Differentiation of the Causal Agent of Citrus Black Spot in Brazil

The Scientific World JOURNAL ◽

10.1100/2012/368286 ◽

2012 ◽

Vol 2012 ◽

pp. 1-14 ◽

Cited By ~ 4

Author(s):

Ester Wickert ◽

Antonio de Goes ◽

Andressa de Souza ◽

Eliana Gertrudes de Macedo Lemos

Keyword(s):

Genetic Diversity ◽

Genetic Structure ◽

Population Differentiation ◽

Sweet Orange ◽

Black Spot ◽

Pathogenic Fungi ◽

Its2 Region ◽

Citrus Black Spot ◽

Different Populations ◽

Different Origins

One of the most important diseases that affect sweet orange orchards in Brazil is the Citrus Black Spot that is caused by the fungusGuignardia citricarpa. This disease causes irreparable losses due to the premature falling of fruit, as well as its severe effects on the epidermis of ripe fruit that renders them unacceptable at the fresh fruit markets. Despite the fact that the fungus and the disease are well studied, little is known about the genetic diversity and the structure of the fungi populations in Brazilian orchards. The objective of this work was study the genetic diversity and population differentiation ofG. citricarpaassociated with four sweet orange varieties in two geographic locations using DNA sequence of ITS1-5.8S-ITS2 region from fungi isolates. We observed that different populations are closely related and present little genetic structure according to varieties and geographic places with the highest genetic diversity distributed among isolates of the same populations. The same haplotypes were sampled in different populations from the same and different orange varieties and from similar and different origins. If new and pathogenic fungi would become resistant to fungicides, the observed genetic structure could rapidly spread this new form from one population to others.

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