scholarly journals First Report of Powdery Mildew Caused by an Oidium sp. on Torenia fournieri

Plant Disease ◽  
1999 ◽  
Vol 83 (9) ◽  
pp. 878-878 ◽  
Author(s):  
G. E. Holcomb
Keyword(s):  
Powdery Mildew ◽  
Infected Plant ◽  
Hyphal Growth ◽  
The United States ◽  
Plant Leaves ◽  
Torenia Fournieri ◽  
Bedding Plant ◽  
Leaf Surfaces ◽  
Powdery Mildew Fungi ◽  
Leaf Distortion

Torenia fournieri Lind. ex Fourn. (wishbone flower, bluewings) is a popular summer bedding plant in Louisiana. Clown Mixture cultivars are available in garden centers in March and April. Transplants of cultivar Clown Rose were purchased, transplanted to larger pots, and maintained in a greenhouse. A powdery mildew was observed on these plants in March and all plants (six) were severely diseased by May. Symptoms included leaf distortion and yellowing. Powdery mildew was not present on transplants and none was found in later checks of garden centers. An Oidium sp. was observed sporulating on both leaf surfaces of infected plants. Conidia were ellipsoid, produced in chains, lacked fibrosin bodies, and averaged 41 × 22 μm in dimensions. No sexual stage was observed. Healthy plants of Clown Mixture cultivars were obtained and inoculated by brushing conidia from infected plant leaves to leaves of healthy plants. Plants were maintained in a greenhouse where temperatures ranged from 16 to 26°C. Hyphal growth appeared on inoculated plants after 5 days and the reproductive structures formed later appeared the same as those on originally infected plants. Uninoculated plants remained healthy. No previous reports of powdery mildew diseases of T. fournieri in the United States were found. Other powdery mildew pathogens reported on T. fournieri are Sphaerotheca fuliginea (Schlechtend.:Fr.) Pollacci in Finland and Japan and an Erysiphe sp. in Japan (1). Reference: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Press, Tokyo, 1986.

scholarly journals First Report of Powdery Mildew Caused by an Oidium sp. on Banana Shrub (Michelia figo)

Plant Disease ◽  
1999 ◽  
Vol 83 (2) ◽  
pp. 198-198 ◽  
Author(s):  
G. E. Holcomb
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Baton Rouge ◽  
The United States ◽  
Sexual Stage ◽  
First Report ◽  
Leaf Chlorosis ◽  
Leaf Surfaces ◽  
Powdery Mildew Fungi ◽  
Severity Of The Disease

Banana shrub (Michelia figo (Lour.) Spreng.) is an evergreen grown in southern landscapes in hardiness zones 7 to 9. A powdery mildew disease has been observed sporadically on this plant for several years in the Baton Rouge area during fall months, but symptoms were always mild. During the summer and fall of 1998, banana shrub plants were observed with moderately severe powdery mildew infections that resulted in leaf chlorosis, distortion, and some defoliation. An Oidium sp. was present on both leaf surfaces, but sporulation was more abundant on the abaxial surfaces. Conidia were ellipsoid, produced in chains, devoid of conspicuous fibrosin bodies, and averaged 37 × 19 μm. No sexual stage was found. Conidia brushed from infected leaves to healthy leaves of a potted banana shrub maintained in a greenhouse caused new infections in 5 to 8 days. Factors responsible for the increased severity of the disease in 1998 are unknown, but the unusually dry summer may have contributed to the increased incidence of this disease. An Oidium sp. was listed on M. figo in Australia and the United States (1), but no other reports were found to confirm this. This is the first report of the occurrence of a powdery mildew on M. figo in the United States. Reference: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Press, Tokyo, 1986.

Development of a diagnostic assay for race differentiation of Podosphaera macularis

Plant Disease ◽  
2020 ◽  
Author(s):  
Mary Block ◽  
Brian Knaus ◽  
Michele S. Wiseman ◽  
Niklaus J. Grünwald ◽  
David H. Gent
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
The United States ◽  
Epidemiological Studies ◽  
Locked Nucleic Acid ◽  
Nucleotide Polymorphisms ◽  
Practical Applications ◽  
Powdery Mildew Fungi ◽  
Perfect Discrimination ◽  
Podosphaera Macularis

Hop powdery mildew (caused by Podosphaera macularis) was confirmed in the Pacific Northwest in 1996. Before 2012, the most common race of P. macularis was able to infect plants that possessed powdery mildew resistance based on the R-genes Rb, R3, and R5. After 2012, two additional races of P. macularis were discovered that can overcome the resistance gene R6 and the partial resistance found in the cultivar Cascade. These three races now occur throughout the region, which can complicate management and research efforts because of uncertainty on which race(s) may be present in the region and able to infect susceptible hop genotypes. Current methods for determining the races of P. macularis are labor intensive, costly, and typically require more than 14 days to obtain results. We sought to develop a molecular assay to differentiate races of the fungus possessing virulence on plants with R6, referred to as V6-virulent, from other races. The transcriptomes of 46 isolates of P. macularis were sequenced to identify loci and variants unique to V6-isolates. Fourteen primer pairs were designed for 10 candidate loci that contained single nucleotide polymorphisms (SNP) and short insertion-deletion polymorphisms. Two differentially-labeled locked nucleic acid probes were designed for a contig that contained a conserved SNP associated with V6-virulence. The resulting duplexed real-time PCR assay was validated against 46 V6 and 54 non-V6 P. macularis isolates collected from the United States and Europe. The assay had perfect discrimination of V6-virulence among isolates of P. macularis originating from the western U.S. but failed to predict V6-virulence in three isolates collected from Europe. The specificity of the assay was tested with different species of powdery mildew fungi and other microorganisms associated with hop. Weak non-specific amplification occurred with powdery mildew fungi collected from Vitis vinifera, Fragaria sp., and Zinnia sp.; however, non-specification amplification is not a concern when differentiating pathogen race from colonies on hop. The assay has practical applications in hop breeding, epidemiological studies, and other settings where rapid confirmation of pathogen race is needed.

scholarly journals Perpetuation of Powdery Mildew Infection and Identification of Erysiphe australiana as the Crape Myrtle Pathogen in Mid-Tennessee

Plant Disease ◽  
2006 ◽  
Vol 90 (8) ◽  
pp. 1098-1101 ◽  
Author(s):  
Ainong Shi ◽  
Margaret T. Mmbaga
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
The United States ◽  
Diagnostic Tools ◽  
Specific Primers ◽  
Standard Polymerase Chain Reaction ◽  
Common Lilac ◽  
Pcr Products ◽  
Powdery Mildew Fungi ◽  
Powdery Mildew Pathogen

The fungus Erysiphe lagerstroemiae is commonly known as the powdery mildew pathogen in crape myrtle (Lagerstroemiae indica) in the United States, and Erysiphe australiana is the powdery mildew pathogen reported in Japan, China, and Australia. The teleomorph often used to identify powdery mildew fungi rarely develops in crape myrtle, and in our observations, ascocarps never formed. Our study showed that the crape myrtle pathogen overwintered as mycelia on dormant buds. The internal transcribed spacer (ITS) regions of rDNA and the intervening 5.8S rRNA gene were amplified using standard polymerase chain reaction (PCR) protocols and the universal primer pairs ITS1 and ITS4. PCR products were analyzed by electrophoresis in a 1.5% agarose gel and sequenced, and the ITS PCR product was 666 bp from ITS1/ITS4 and 704 bp from ITS1-F/ITS4. BLAST analysis of the sequence of the PCR products showed identical similarity with E. australiana reported in Japan, China, and Australia. Comparison of ITS sequences with information in the GenBank on other powdery mildew fungi showed a closest alignment (93% similarity) to Erysiphe juglandis that infects walnut. Specific primers for E. australiana were developed and evaluated for use as diagnostic tools. Out of 12 specific primer pairs evaluated, four primer pairs and four double primer pairs were highly specific to E. australiana and did not amplify Erysiphe pulchra of dogwood, Erysiphe syringae of common lilac, Erysiphe circinata of maple, or Phyllactinia guttata of oak. The E. australiana-specific primers amplified 16 samples of crape myrtle powdery mildew collected from diverse locations in mid-Tennessee. These results clearly showed that the crape myrtle powdery mildew in mid-Tennessee was caused by E. australiana. Specific primers reported in this article provide a diagnostic tool and may be used to confirm the identity of crape myrtle powdery mildew pathogen in other areas in the United States and wherever the disease occurs.

scholarly journals A Pattern Recognition Tool for Quantitative Analysis of In Planta Hyphal Growth of Powdery Mildew Fungi

2005 ◽  
Vol 18 (9) ◽  
pp. 906-912 ◽  
Author(s):  
U. Seiffert ◽  
P. Schweizer
Keyword(s):  
Growth Rate ◽  
Pattern Recognition ◽  
Quantitative Analysis ◽  
Powdery Mildew ◽  
Growth Rates ◽  
Fungal Pathogens ◽  
Hyphal Growth ◽  
Blumeria Graminis ◽  
In Planta ◽  
Powdery Mildew Fungi

The development of fungal pathogens can be quantified easily at the level of spore germination or penetration. However, the exact quantification of hyphal growth rates after initial, successful host invasion is much more difficult. Here, we report on the development of a new pattern recognition software (HyphArea) for automated quantitative analysis of hyphal growth rates of powdery mildew fungi on plant surfaces that usually represent highly irregular and noisy image backgrounds. By using HyphArea, we measured growth rates of colonies of the barley powdery mildew, Blumeria graminis f. sp. hordei, on susceptible and induced-resistant host plants. Hyphal growth was not influenced by the resistance state of the plants up to 48 h postinoculation. At later time points, growth rate increased on susceptible plants, whereas it remained restricted on induced-resistant plants. This difference in hyphal growth rate was accompanied by lack of secondary haustoria formation on induced-resistant plants, suggesting that induced resistance in barley against Blumeria graminis is caused mainly by reduced penetration rates of primary as well as secondary appressoria leading, finally, to fewer and lessdeveloped fungal colonies. No evidence was found for reduced nutrient-uptake efficiency of the primary haustoria in induced-resistant leaves, which would be expected to have resulted in reduced hyphal growth rates during the first 48 h of the interaction.

scholarly journals Golovinomyces biocellatus on Oregano (Origanum vulgare ‘Compactum’) in Italy

Plant Disease ◽  
2012 ◽  
Vol 96 (3) ◽  
pp. 457-457
Author(s):  
A. Garibaldi ◽  
D. Bertetti ◽  
P. Martini ◽  
L. Repetto ◽  
M. L. Gullino
Keyword(s):  
Powdery Mildew ◽  
Signs And Symptoms ◽  
Its Region ◽  
Pathogenicity Test ◽  
Academic Press ◽  
Conidial Suspension ◽  
Origanum Vulgare ◽  
Leaf Surfaces ◽  
Powdery Mildew Fungi ◽  
Voucher Specimens

Origanum vulgare L., common name oregano, also known as pot marjoram, Lamiaceae family, is grown for its aromatic and medicinal properties and as an ornamental. In particular, O. vulgare ‘Compactum’ is becoming popular as a potted plant. During January 2011, 3-month-old plants grown on a commercial farm located near Albenga (northern Italy) showed signs and symptoms of an unknown powdery mildew. Ninety percent of the plants were affected. The adaxial leaf surfaces were covered with white mycelia and conidia, while the abaxial surfaces were less infected. As the disease progressed, infected leaves turned yellow, wilted, and eventually fell off. Mycelia were also observed on stems. Conidia were hyaline, elliptical, borne single or in short chains (three to four conidia per chain), and measured 37.9 × 19.6 (31.2 to 45.1 × 14.9 to 26.2) μm. Conidiophores were erect with a cylindrical foot cell measuring 81.1 × 9.7 (54.2 to 112.4 × 7.9 to 11.6) μm followed by two to three shorter cells measuring 26.8 × 11.8 (16.6 to 38.1 × 8.5 to 15.3) μm. Fibrosin bodies were absent. Chasmothecia were not observed in the collected samples. The internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1F/ITS4 and sequenced (3) (GenBank Accession No. JN594608). The 560-bp amplicon had 99% homology with the sequence of Golovinomyces biocellatus (GenBank Accession No. AB307675). Pathogenicity was confirmed through inoculation by spraying a conidial suspension (6 × 104 CFU/ml) prepared from diseased leaves onto leaves of healthy O. vulgare ‘Compactum’ plants. Four plants were inoculated while the same number of noninoculated plants served as a control. Plants were maintained in a glasshouse at temperatures ranging from 23 to 28°C. Ten days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. The fungus observed on inoculated plants was morphologically identical to that originally observed. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. G. biocellatus on O. vulgare has been reported in Switzerland (2) and Argentina (4) and it is present on other plant genera in Italy. In Italy, on the same host, attacks of Erysiphe galeopsis have been previously reported (1). The economic importance of this disease is currently limited due to limited planting of this species. However, in the last years, potted aromatic plants represent a steady increasing crop in Italy. Voucher specimens are available at the Agroinnova Collection, University of Torino. References: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Science Society Press, Tokyo, 1986. (2) A. Bolay. Cryptog. Helv. 20:1, 2005. (3) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990. (4) S. M. Wolcan. J. Plant Patho. 91:501, 2009.

scholarly journals Occurrence of Alfalfa mosaic virus in Soybean in Tennessee

Plant Disease ◽  
2010 ◽  
Vol 94 (12) ◽  
pp. 1505-1505 ◽  
Author(s):  
O. L. Fajolu ◽  
R.-H. Wen ◽  
M. R. Hajimorad
Keyword(s):  
United States ◽  
Mosaic Virus ◽  
Natural Infection ◽  
Infected Plant ◽  
Alfalfa Mosaic Virus ◽  
The United States ◽  
Soybean Plant ◽  
Wide Range ◽  
Soybean Plants ◽  
Leaf Distortion

Alfalfa mosaic virus (AMV), a member of the genus Alfamovirus in the family Bromoviridae, naturally infects a wide range of plant species (1). Soybean (Glycine max (L.) Merr.) has seldom been reported as a natural host of AMV and there are limited reports of detection of AMV in field-grown soybean plants (4). However, AMV incidence in soybean fields in the midwestern United States has been on the rise in recent years, which is partly attributed to the introduction of the soybean aphid (Aphis glycines) (1,4). In June 2009, soybean plants of cv. Lee68 exhibiting moderate leaf distortion, mottling, and stunting were observed at the East Tennessee Research and Education Center. Leaf samples from 18 symptomatic plants were collected and the sap was extracted and analyzed by antigen-coated indirect ELISA (3) with polyclonal antibodies against AMV, Soybean mosaic virus (SMV), and Bean pod mottle virus (BPMV). None of the samples tested positive for BPMV, but all were found to be infected with SMV. Sap extract from 1 of 18 plants tested positive for AMV and SMV. Sap from this infected plant ground in 10 mM phosphate buffer, pH 7.0, was mechanically inoculated to Carborundum-dusted unifoliate leaves of PI96983, which contains the dominant Rsv1-locus conferring functional immunity to a majority of SMV strains (2). AMV, not SMV, was detected by ELISA in the systemically infected trifoliolate leaves that exhibited moderate mottling, mild leaf distortion, and stunting 14 days postinoculation. Sap was extracted from the infected tissues and the virus was passaged four times through PI96983 before being inoculated to Phaseolus vulgaris cv. Blue Lake. A local lesion isolate was obtained following three successive passages in this host and the isolate was propagated in soybean cv. Williams82. The biologically purified isolate was capable of infecting soybean cvs. L78-379 (Rsv1), L81-4420 (Rsv1), L29 (Rsv3), V94-5152 (Rsv4), Lee68, and Colfax upon sap inoculation. The infected plants exhibited a range of systemic symptoms including mottling, leaf distortion, necrosis, chlorosis, and moderate stunting. To characterize the virus further, total RNA was extracted from infected Williams82 leaf tissues with the RNeasy Plant Mini Kit (Qiagen, Valencia, CA). The RNA served as a template for cDNA synthesis in the presence of random primers. The resultant cDNA served as a template in a PCR assay with primers 1193 (forward) (5′-AGCTGAATTCATGAGTTCTTCACAAC-3′) and 1858 (reverse) (5′-GCTAGCGGCCGCTCAATGACGATC-3′) corresponding to nucleotides 1,193 to 1,210 and 1,858 to 1,840 of RNA3 from AMV-Kr (GenBank Accession No. AB126032), respectively. The amplified fragments were purified and directly sequenced bidirectionally using the same primers. BLAST analysis of the resultant nucleotide sequences showed 98% identity to an AMV isolate from a naturally infected soybean plant in Illinois (GenBank Accession No. HQ185569), and 97% identity to an isolate described from P. vulgaris in the United States (GenBank Accession No. AY340070.1). To our knowledge, this is the first report of natural infection of soybean by AMV in Tennessee. References: (1) J. Bol. Mol. Plant Pathol. 4:1, 2003. (2) M. R. Hajimorad and J. H. Hill. Mol. Plant-Microbe Interact. 14:587, 2001. (3) M. Malapi-Nelson et al. Plant Dis. 93:1259, 2009. (4) E. E. Mueller and C. R. Grau. Plant Dis. 91:266, 2007.

scholarly journals A Mobile-Based System for Detecting Plant Leaf Diseases Using Deep Learning

2021 ◽  
Vol 3 (3) ◽  
pp. 478-493
Author(s):  
Ahmed Abdelmoamen Ahmed ◽  
Gopireddy Harshavardhan Reddy
Keyword(s):  
Deep Learning ◽  
Classification Accuracy ◽  
Infected Plant ◽  
The United States ◽  
Disease Diagnosis ◽  
Mobile App ◽  
Plant Diseases ◽  
Plant Leaves ◽  
Plant Leaf ◽  
Crop Diseases

Plant diseases are one of the grand challenges that face the agriculture sector worldwide. In the United States, crop diseases cause losses of one-third of crop production annually. Despite the importance, crop disease diagnosis is challenging for limited-resources farmers if performed through optical observation of plant leaves’ symptoms. Therefore, there is an urgent need for markedly improved detection, monitoring, and prediction of crop diseases to reduce crop agriculture losses. Computer vision empowered with Machine Learning (ML) has tremendous promise for improving crop monitoring at scale in this context. This paper presents an ML-powered mobile-based system to automate the plant leaf disease diagnosis process. The developed system uses Convolutional Neural networks (CNN) as an underlying deep learning engine for classifying 38 disease categories. We collected an imagery dataset containing 96,206 images of plant leaves of healthy and infected plants for training, validating, and testing the CNN model. The user interface is developed as an Android mobile app, allowing farmers to capture a photo of the infected plant leaves. It then displays the disease category along with the confidence percentage. It is expected that this system would create a better opportunity for farmers to keep their crops healthy and eliminate the use of wrong fertilizers that could stress the plants. Finally, we evaluated our system using various performance metrics such as classification accuracy and processing time. We found that our model achieves an overall classification accuracy of 94% in recognizing the most common 38 disease classes in 14 crop species.

scholarly journals First Report of Leveillula taurica Causing Powdery Mildew on Pepper in Maryland

Plant Disease ◽  
2009 ◽  
Vol 93 (11) ◽  
pp. 1222-1222 ◽  
Author(s):  
R. W. Jones ◽  
J. R. Stommel ◽  
L. A. Wanner
Keyword(s):  
Powdery Mildew ◽  
Infected Plant ◽  
Pcr Amplification ◽  
The United States ◽  
Bell Pepper ◽  
Leaf Damage ◽  
Pepper Plant ◽  
Breeding Lines ◽  
Leveillula Taurica ◽  
Pepper Plants

Pepper plants in large experimental plots in Beltsville, MD developed widespread powdery mildew during the late summer of 2008. Infection was observed in a diversity of accessions that included Capsicum annuum, C. baccatum, C. chinense, and C. frutescens (2). The C. annuum accessions included culinary bell pepper cultivars and breeding lines as well as a diverse collection of ornamental breeding lines, heirlooms, and land races. Significant leaf damage occurred and led to partial defoliation. Extensive coverage of the abaxial surface by white patches of conidia was noted, along with chlorotic regions on the adaxial surface. Conidia were borne singly and were apically tapered, measuring 65.2 ± 3.2 × 14.9 ± 1.9 μm. Cleistothecia were not found on infected leaves (3). PCR amplification of the internal transcribed spacer (ITS) region using ITS1-2 primers yielded a band that was cloned and sequenced (4). The pathogen was identified as Leveillula taurica based on 100% homology to GenBank Accession No. AY912077. Multiple chili pepper and bell pepper plants were inoculated with conidia from an infected bell pepper plant by placement in an enclosed spore deposition chamber for 1 week, with the infected plant suspended over the test plants. Signs of powdery mildew appeared only on inoculated plants. DNA samples from these inoculated plants were analyzed and verified as L. taurica (a sequence was deposited as GenBank No. GQ167201). A second set of inoculations using the newly infected plants confirmed results of the first test, with mildew developing only on inoculated pepper plants. This disease is new to the mid-Atlantic Region of the United States. It has been reported in greenhouse peppers growing in Ontario, Canada where it has become a recurring problem requiring fungicide intervention (1). Given the wide host range of L. taurica and the systemic nature of infections, it is likely that the fungus has become established in Maryland on perennial host plants. References: (1) R. Cerkauskas. Plant Dis. 83:781, 1999. (2) V. de Souza. Plant Pathol. 52:613, 2003. (3) C. Little. Plant Dis. 90:1358, 2006. (4) G. Saenz. Can. J. Bot. 77:150, 1999.

scholarly journals Outbreak of Powdery Mildew on Common Sage in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (8) ◽  
pp. 911-911 ◽  
Author(s):  
M. Madia ◽  
S. Gaetán
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Disease Incidence ◽  
Signs And Symptoms ◽  
The United States ◽  
Erysiphe Cichoracearum ◽  
Leaf Surfaces ◽  
Pathogenicity Tests ◽  
Salvia Officinalis L ◽  
Autumn And Winter

Common sage, Salvia officinalis L., is produced primarily in greenhouses for the culinary herb market in Argentina. Since 2003 during autumn and winter, powdery mildew symptoms have been repeatedly observed on potted common sage plants in commercial greenhouses located on the outskirts of Buenos Aires. The average disease incidence during this period was 85 to 90%. Circular, white, powdery patches developed on leaf surfaces and stems. Heavily infected leaves turned brown and died. Hyaline mycelium and nonlobed appressoria were observed. Conidiophores were simple with straight foot cells measuring 53.0 to 80.0 × 10.0 to 12.3 μm. Conidia were aseptate, hyaline, cylindrical to ovoid, measured 33.0 to 40.5 × 15.0 to 18.5 μm, did not contain fibrosine bodies, and were produced in chains. Cleistothecia were not observed. The pathogen was identified as Erysiphe cichoracearum DC (1). Pathogenicity was confirmed by gently pressing leaves displaying abundant sporulation onto the adaxial surface of healthy leaves. After 10 to 12 days, typical signs and symptoms of powdery mildew appeared on all inoculated plants. Pathogenicity tests were conducted in a greenhouse at 20 to 23°C and included 10 sage plants (five inoculated and five noninoculated). The experiment was performed twice, each time with the same result. Control plants did not show any signs or symptoms. E. cichoracearum DC was previously reported in the United States on Salvia sp. (2).To our knowledge, this is the first report of an outbreak of powdery mildew caused by E. cichoracearun on potted common sage plants produced in greenhouses in Argentina. References: (1) H. J. Boesewinkel. Rev. Mycol. Tome 41:493, 1977. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.

scholarly journals First Report of Powdery Mildew on Azalea Caused by Erysiphe azaleae in Louisiana

Plant Disease ◽  
2006 ◽  
Vol 90 (9) ◽  
pp. 1263-1263
Author(s):  
G. E. Holcomb ◽  
D. M. Ferrin
Keyword(s):  
Powdery Mildew ◽  
Baton Rouge ◽  
The United States ◽  
Fungal Mycelium ◽  
Pigment Formation ◽  
First Report ◽  
Leaf Drop ◽  
Conidia Production ◽  
Leaf Distortion ◽  
Symptoms And Signs

A group of five cv. Red Formosa azaleas (also known as cv. Dixie Beauty, an evergreen indica type of Rhododendron indicum) was observed with powdery mildew symptoms in Baton Rouge, LA in early March 2006. Symptoms included leaf distortion, purple leaf pigmentation at infection sites, and irregular necrotic areas. White, sparse, superficial fungal mycelium was present on both leaf surfaces. There was no active conidia production at this time and no cleistothecia were found on the old infected leaves. Infected plants were 5 years old and growing in heavy shade beneath a large deciduous oak tree. Two other groups of powdery mildew-free cv. Red Formosa, containing 6 and 11 plants each, were growing in mostly shade-free areas within 30 and 140 m, respectively, of the infected plants. Of 5,091 azaleas surveyed in and around Baton Rouge, only three other infected plants were found beside the original five. Among the plants surveyed were 167 additional cv. Red Formosa azaleas. The three additional infected azaleas, all the same unidentified indica type cultivar and growing in dense shade, showed severe leaf distortion and leaf drop. Conidia were produced abundantly on these plants in April and early May, but the teleomorph was not found. Pathogenicity tests were performed by rubbing leaves with sporulating powdery mildew from infected cv. Red Formosa plants on terminal leaves of two branches each of three 1-gallon-container plants of the same cultivar. A clear plastic bag containing a damp paper towel was placed over each inoculated branch for 48 h and then removed. Noninoculated branches on the same plants served as controls. Plants were maintained in a greenhouse (21 to 27°C). After 5 days, the first symptoms and signs of infection appeared on inoculated leaves in the form of purple pigment formation and white sporulating mycelia. After 12 days, terminal leaves on all inoculated branches showed symptoms and signs of powdery mildew, and after 18 days, leaf puckering and irregular necrotic spotting was common; purple pigmentation often outlined infected areas in which white mycelia and conidia production occurred. Some sporulation was present on petioles and some leaf drop occurred. The foliage on noninoculated branches remained disease free. Conidia from original infected plants were produced singly, ellipsoid to cylindric, lacked fibrosin bodies, and measured 27 to 54 μm long (mean = 37.4, standard error (SE) = 0.19, n = 102) × 15 to 23 μm wide (mean = 17.4, SE = 0.13, n = 102). Conidia sometimes formed short chains of two to four on inoculated plants held in the greenhouse. Conidiophores measured 77 to 123 μm long (mean = 106, SE = 1.1, n = 12) × 7 to 10 μm wide (mean = 8.9, SE = 0.26, n = 12) and had curved or twisted bases. Appressoria were multilobed. On the basis of these characters, the anamorph of the azalea powdery mildew was identified as Oidium ericinum Erikss. = Erysiphe (Microsphaera) azaleae (U. Braun) U. Braun & S. Takam. (1,2,4). To our knowledge, this is the first report on the occurrence of azalea powdery mildew in Louisiana. Powdery mildew is more common on deciduous than on evergreen azaleas and is more common in northern parts of the United States, especially in the Pacific Northwest (3). References: (1) U. Braun. Nova Hedwigia Suppl. 89:1, 1987. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:5, 2000. (3) M. L. Daughtrey and D. M. Benson. Rhododendron diseases. Page 339 in: Diseases of Woody Ornamentals and Trees in Nurseries. R. K. Jones and D. M. Benson, eds. The American Phytopathological Society. St. Paul, MN, 2001. (4) A. J. Inman et al. J. Phytopathol. 148:17, 2000.

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