scholarly journals 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 ◽  
2016 ◽  
Vol 51 (12) ◽  
pp. 1555-1560 ◽  
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.

scholarly journals Baseline Sensitivity of Guignardia citricarpa Isolates from Florida to Azoxystrobin and Pyraclostrobin

Plant Disease ◽  
2014 ◽  
Vol 98 (6) ◽  
pp. 780-789 ◽  
Author(s):  
Martha Hincapie ◽  
Nan-Yi Wang ◽  
Natalia A. Peres ◽  
Megan M. Dewdney
Keyword(s):  
Mycelial Growth ◽  
Control Measure ◽  
Black Spot ◽  
Conidial Germination ◽  
Baseline Sensitivity ◽  
Qoi Fungicides ◽  
Resistance Risk ◽  
Guignardia Citricarpa ◽  
The Mean

Citrus black spot (CBS), caused by Guignardia citricarpa, is an emerging disease in Florida. Fungicide applications are the main control measure worldwide. The in vitro activity and baseline sensitivity of G. citricarpa isolates to quinone outside inhibitor (QoI) fungicides (azoxystrobin and pyraclostrobin) were evaluated. The effective concentration needed to reduce mycelial growth or spore germination by 50% (EC50) was determined for 86 isolates obtained from Florida counties where CBS is found. The effect of salicylhydroxamic acid (SHAM) plus azoxystrobin and pyraclostrobin was also assessed for mycelial growth and conidial germination. The mean EC50 for mycelial growth for azoxystrobin was 0.027 μg/ml and that for pyraclostrobin was significantly lower at 0.007 μg/ml (P < 0.0001). Similarly, the mean EC50 for conidial germination for azoxystrobin was 0.016 μg/ml and that for pyraclostrobin was significantly lower at 0.008 μg/ml (P < 0.0001). There was no effect of SHAM on inhibition of mycelial growth or conidial germination by the QoI fungicides but SHAM slightly affected mycelium inhibition by pyraclostrobin. Cytochrome b was partially sequenced and three group 1 introns were found. One intron was immediately post G143, likely inhibiting resistance-conferring mutations at that site. It is surmised that the QoI resistance risk is low in the Florida G. citricarpa population.

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

Plant Disease ◽  
2019 ◽  
Vol 103 (5) ◽  
pp. 913-921 ◽  
Author(s):  
Guilherme F. Frare ◽  
Geraldo J. Silva-Junior ◽  
Fabrício E. Lanza ◽  
Renato B. Bassanezi ◽  
Thiago G. Ramires ◽  
...  
Keyword(s):  
Incubation Period ◽  
Sweet Orange ◽  
Disease Incidence ◽  
Black Spot ◽  
Conidial Germination ◽  
Inoculum Concentration ◽  
Factors Affecting ◽  
Citrus Black Spot ◽  
Incubation Periods ◽  
Orange Fruit

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.

scholarly journals In vitro effect of UV-C irradiation on Guignardia citricarpa and on postharvest control of citrus black spot

2011 ◽  
Vol 36 (6) ◽  
pp. 356-361 ◽  
Author(s):  
Maria C. Canale ◽  
Eliane A. Benato ◽  
Patrícia Cia ◽  
Marineia L. Haddad ◽  
Sérgio F. Pascholati
Keyword(s):  
Black Spot ◽  
Guignardia Citricarpa ◽  
Citrus Black Spot ◽  
Vitro Effect ◽  
Uv C ◽  
Postharvest Control

scholarly journals Improving the Biocontrol Potential of Bacterial Antagonists with Salicylic Acid against Brown Rot Disease and Impact on Nectarine Fruits Quality

Agronomy ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 209
Author(s):  
Nadia Lyousfi ◽  
Rachid Lahlali ◽  
Chaimaa Letrib ◽  
Zineb Belabess ◽  
Rachida Ouaabou ◽  
...  
Keyword(s):  
Salicylic Acid ◽  
Disease Severity ◽  
Mycelial Growth ◽  
Brown Rot ◽  
Antagonistic Bacteria ◽  
Biological Treatments ◽  
Rot Disease ◽  
The Impact

The main objective of this study was to evaluate the ability of both antagonistic bacteria Bacillus amyloliquefaciens (SF14) and Alcaligenes faecalis (ACBC1) used in combination with salicylic acid (SA) to effectively control brown rot disease caused by Monilinia fructigena. Four concentrations of salicylic acid (0.5%, 2%, 3.5%, and 5%) were tested under in vitro and in vivo conditions. Furthermore, the impact of biological treatments on nectarine fruit parameters’ quality, in particular, weight loss, titratable acidity, and soluble solids content, was evaluated. Regardless of the bacterium, the results indicated that all combined treatments displayed a strong inhibitory effect on the mycelial growth of M. fructigena and disease severity. Interestingly, all SA concentrations significantly improved the biocontrol activity of each antagonist. The mycelial growth inhibition rate ranged from 9.79% to 88.02% with the highest reduction rate recorded for bacterial antagonists in combination with SA at both concentrations of 0.5% and 3.5%. The in vivo results confirmed the in vitro results with a disease severity varying from 0.00% to 51.91%. A significant biocontrol improvement was obtained with both antagonistic bacteria when used in combination with SA at concentrations of 0.5% and 2%. The lowest disease severity observed with ACBC1 compared with SF14 is likely due to a rapid adaptation and increase of antagonistic bacteria population in wounded sites. The impact of all biological treatments revealed moderate significant changes in the fruit quality parameters with weight loss for several treatments. These results suggest that the improved disease control of both antagonistic bacteria was more likely directly linked to both the inhibitory effects of SA on pathogen growth and induced fruit resistance.

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 Evaluation of various plant extracts against the early blight disease of tomato plants under greenhouse and field conditions

2012 ◽  
Vol 48 (No. 2) ◽  
pp. 74-79 ◽  
Author(s):  
S.M.A. Nashwa ◽  
K.A.M. Abo-Elyousr
Keyword(s):  
Disease Severity ◽  
Plant Extracts ◽  
Mycelial Growth ◽  
Early Blight ◽  
Field Conditions ◽  
Nerium Oleander ◽  
Tomato Plants ◽  
Infected Control ◽  
Blight Disease

The antimicrobial activity of six plant extracts from Ocimum basilicum (Sweat Basil), Azadirachta indica (Neem), Eucalyptus chamadulonsis (Eucalyptus), Datura stramonium (Jimsonweed), Nerium oleander (Oleander), and Allium sativum (Garlic) was tested for controlling Alternaria solani in vitro and in vivo. In in vitro study the leaf extracts of D. stramonium, A. indica, and A. sativum at 5% concentration caused the highest reduction of mycelial growth of A. solani (44.4, 43.3 and 42.2%, respectively), while O. basilicum at 1% and 5% concentration and N. oleander at 5% concentration caused the lowest inhibition of mycelial growth of the pathogen. In greenhouse experiments the highest reduction of disease severity was achieved by the extracts of A. sativum at 5% concentration and D. stramonium at 1% and 5% concentration. The greatest reduction of disease severity was achieved by A. sativum at 5% concentration and the smallest reduction was obtained when tomato plants were treated with O. basilicum at 1% and 5% concentration (46.1 and 45.2 %, respectively). D. stramonium and A. sativum at 5% concentration increased the fruit yield by 76.2% and 66.7% compared to the infected control. All treatments with plant extracts significantly reduced the early blight disease as well as increased the yield of tomato compared to the infected control under field conditions.

scholarly journals AVALIAÇÃO DO REAL POTENCIAL INIBIDOR DE EXTRATOS ETANÓLICOS DE Ottonia martiana SOBRE Cylindrocladium spathulatum E Botrytis cinerea

FLORESTA ◽  
2013 ◽  
Vol 43 (2) ◽  
pp. 225
Author(s):  
Miriam Machado Cunico ◽  
Celso Garcia Auer ◽  
Marlon Wesley Machado Cunico ◽  
Obdulio Gomes Miguel ◽  
Patricio Peralta Zamora ◽  
...  
Keyword(s):  
Factorial Design ◽  
Botrytis Cinerea ◽  
Mycelial Growth ◽  
Black Spot ◽  
Gray Mold ◽  
Causal Agent ◽  
In Vitro Testing ◽  
Ethanolic Extracts ◽  
Antifungal Potential

 Extratos etanólicos de anestesia, Ottonia martiana Miq., foram reavaliados quanto à inibição do crescimento micelial dos fungos Cylindrocladium spathulatum (pinta-preta da erva-mate) e Botrytis cinerea (mofo-cinzento do eucalipto), por meio do planejamento fatorial. A ocorrência de decomposição de bioativos no processo de autoclavagem também foi investigada, por meio de teste de eficiência de extratos filtrados (filtro Millipore) e esterilizados (autoclave) no controle dos fitopatógenos, nas concentrações de 1, 10, 100 e 1000 ppm. Os extratos etanólicos filtrado e esterilizado inibiram o crescimento micelial dos fungos e foram mais ativos frente a B. cinerea.O extrato filtrado exibiu maior potencial antifúngico que o extrato esterilizado. O processo de esterilização por autoclavagem causou pequena decomposição dos bioativos presentes no extrato de anestesia.Palavras-chave: Anestesia; mofo-cinzento; pinta-preta. Abstract Fungitoxic potential of ethanolic extracts of anestesia in the control of phytopathogenic diseases. The antifungal potential of anestesia, Ottonia martiana Miq. was reassessed by factorial design, in vitro testing of fungal mycelial growth compared to the pathogenic isolates Cylindrocladium spathulatum, causal agent of black spot onyerba mate, and Botrytis cinerea causal agent of gray-mold on eucalypts. Occurrence of decomposition of bioactive of the autoclaving process was investigated using foliar detached test compared to the pathogens (1000 ppm). Ethanolic extracts - EBEtOH (filtered and autoclaved) inhibited the mycelial growth of C. spathulatum and B. cinerea (1000 ppm) and were more pronounced against B. cinerea (43.6 % and 68.9 %). EBEtOH filtered (0.22 µm) presented higher activity than EBEtOH autoclaved (C. spathulatum: 52.8 % and 43.6 %, B. cinerea: 68.9 % and 43.6 %), suggesting little decomposition ofbioactive after autoclaving. EBEtOH filtrate presented potential inhibition of 28 % in eucalypt leaves against B. cinerea.  Keywords: Ottonia martiana; black spot; gray-mold.

scholarly journals A One-Day Sensitive Method to Detect and Distinguish Between the Citrus Black Spot Pathogen Guignardia citricarpa and the Endophyte Guignardia mangiferae

Plant Disease ◽  
2006 ◽  
Vol 90 (1) ◽  
pp. 97-101 ◽  
Author(s):  
L. Meyer ◽  
G. M. Sanders ◽  
R. Jacobs ◽  
L. Korsten
Keyword(s):  
South African ◽  
Sequence Data ◽  
Black Spot ◽  
The United States ◽  
Guignardia Citricarpa ◽  
Competitive Edge ◽  
Citrus Black Spot ◽  
Species Specific ◽  
Time Required ◽  
Slow Growing

If South African citrus exporters wish to retain their competitive edge in the European market and access new markets such as the United States of America, it is of quarantine importance to distinguish between the citrus black spot pathogen, Guignardia citricarpa, and the harmless endophyte, G. mangiferae. The endophyte is not a sanitary or phytosanitary concern. This paper describes the design of species-specific primers that are able to detect and distinguish between these two Guignardia species. Application of the primer set CITRIC1 and CAMEL2 in conjunction with the ITS4 primer yielded polymerase chain reaction (PCR) amplicons of approximately 580 bp and 430 bp for G. citricarpa and G. mangiferae, respectively. Results obtained with these primers are in accordance with sequence data, and repeated tests verified accuracy and sensitivity. A BLAST search revealed no matches other than G. citricarpa and G. mangiferae, and no positive PCR results were obtained with Colletotrichum gloeosporioides, which is the most common contaminant in black spot lesions. We are, therefore, able to distinguish G. citricarpa and G. mangiferae unequivocally using a PCR-based method. This method was further improved to directly isolate DNA from fruit lesions by means of the DNeasy Plant Mini Kit (Qiagen). This eliminates the prior need for culturing the slow-growing organism, thereby shortening the time required to one day to test for and verify the presence or absence of the pathogenic G. citricarpa in export consignments.

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.

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