First Report of Leaf Blight and Root and Foot Rot of a Strelitzia Caused by Phytophthora nicotianae in Italy

Bird of paradise, also known as crane flower (Strelitzia reginae Aiton), is a monocotyledonous flowering plant indigenous to South Africa. It is commonly grown and commercialized as an ornamental plant and it is appreciated for its beautiful flowers. In October of 2008, dark leaf spots and leaf blight associated with a severe root and foot rot were observed on several plants of S. reginae grown in a private garden located in Fiumicino, Italy. Small fragments of tissues (approximately 3 mm) collected from the base of leaves and roots and the margins of brown lesions, previously surface disinfected with 0.5% NaOCl, were plated onto potato dextrose agar (PDA) and incubated at 22°C in the dark. White, web-like, slow-growing colonies with coenocytic mycelium and hyphal swellings consistently developed from all plated tissue samples. Sporangia were ovoid or ellipsoid with prominent papillae (including some bipapillate) and frequently caducous with a short stalk. The dimensions of sporangia were 27 to 64 × 23 to 45 μm (average 43 × 35 μm). Chlamydospores were terminal or intercalary and approximately 30 μm in diameter. Isolates were considered heterothallic because they did not produce gametangia in vitro or in planta. On the basis of morphological features, isolates were identified as Phytophthora nicotianae (Breda de Haan). The identity was confirmed by internal transcribed spacer (ITS) sequence comparison in NCBI database with 99% identity with sequences available in GenBank (e.g., EU331089) and with cytochrome c oxidase subunit I (Cox I) with 99% identity with AY564196 by Kroon et al. (2). The sequences of one isolate, AB177, were deposited in GenBank (Accession Nos. FN430681 and FN552051 for ITS and Cox I, respectively). Pathogenicity tests were conducted in the greenhouse on leaves of a 1-year-old potted S. reginae plant by placing 5-mm-diameter mycelial plugs, cut from the margins of 10-day-old actively growing cultures, with mycelium in contact with plant tissues gently wounded with a needle. Controls were treated as described above, except that PDA sterile plugs were used. Plants were misted with water and placed in sealed plastic bags for 48 h. After 10 days, artificially wounded strelitzia leaves showed lesions (approximately 1 cm long). Controls remained symptomless. All inoculated leaves showed the same leaf symptoms as observed on naturally diseased plants. The pathogen was consistently reisolated from lesions. P. nicotianae has been reported as the causal agent of leaf blight and stem, collar, and root rot on several plants (1). It has been reported as an agent of Phytophthora blight on strelitzia in Japan (3). To our knowledge, this is the first report of P. nicotianae on strelitzia in Italy. References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) L. P. N. M. Kroon et al. Fungal Genet. Biol. 41:766, 2004. (3) S. Uematsu et al. Ann. Phytopathol. Soc. Jpn. 60:746, 1994.

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Fitness of Isolates of Phytophthora capsici Resistant to Mefenoxam from Squash and Pepper Fields in North Carolina

Plant Disease ◽

10.1094/pdis-92-10-1439 ◽

2008 ◽

Vol 92 (10) ◽

pp. 1439-1443 ◽

Cited By ~ 24

Author(s):

Adalberto C. Café-Filho ◽

Jean Beagle Ristaino

Keyword(s):

North Carolina ◽

Phytophthora Capsici ◽

Colony Growth ◽

Relative Fitness ◽

In Planta ◽

Phytophthora Blight ◽

In Vivo Experiments ◽

First Time

Despite the wide adoption of mefenoxam (Ridomil Gold EC) for vegetables in North Carolina, the incidence of Phytophthora blight on pepper (Capsicum annuum) and squash (Cucurbita pepo) is high. Seventy-five isolates of Phytophthora capsici were collected in five pepper and one squash field in order to assess mefenoxam sensitivity. The relative fitness of resistant and sensitive isolates was contrasted in vitro by their respective rates of colony growth and their ability to produce sporangia in unamended V8 juice agar medium. In in vivo experiments, the aggressiveness of isolates on pepper was evaluated. The frequency of resistant isolates in North Carolina populations was 63%, considerably higher than resistance levels in areas where mefenoxam is not widely adopted. Resistant isolates grew on amended media at rates >80 to 90% and >100% of the nonamended control at 100 μg ml-1 and 5 μg ml-1, respectively. Sensitive isolates did not growth at 5 or 100 μg ml-1. All isolates from three fields, including two pepper and a squash field, were resistant to mefenoxam. Populations from other fields were composed of either mixes of sensitive and resistant isolates or only sensitive isolates. Response to mefenoxam remained stable during the course of in vitro and in planta experiments. Occurrence of a mefenoxam-resistant population of P. capsici on squash is reported here for the first time in North Carolina. When measured by rate of colony growth, sporulation in vitro, or aggressiveness in planta, fitness of resistant isolates was not reduced. Mefenoxam-resistant isolates from squash were as aggressive on pepper as sensitive or resistant pepper isolates. These results suggest that mefenoxam-resistant populations of P. capsici are as virulent and fit as sensitive populations.

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Incidence and Significance of Iprodione-Insensitive Isolates of Botrytis squamosa

Plant Disease ◽

10.1094/pd-91-0041 ◽

2007 ◽

Vol 91 (1) ◽

pp. 41-46 ◽

Cited By ~ 8

Author(s):

O. Carisse ◽

D. M. Tremblay

Keyword(s):

Active Ingredient ◽

Leaf Blight ◽

Conidial Suspension ◽

In Planta ◽

Good Relationship ◽

Percent Inhibition ◽

Botrytis Squamosa ◽

Leaf Lesion ◽

Important Disease

Botrytis leaf blight, caused by Botrytis squamosa, is an economically important disease of onion. The principal means of controlling the disease is by applying fungicides. Typical fungicide programs include applications of dithiocarbamates, chloronitriles, carboxamides, and dicarboximides such as iprodione (Rovral). Onion fields were surveyed in 2002, 2003, and 2004 for insensitivity to iprodione. Tests for insensitivity to iprodione were conducted on 62, 58, and 60 monoconidial field isolates using the automated quantitative (AQ) method with a discriminatory dose of 1.78 ppm of iprodione active ingredient (a.i.) in 2002, 2003, and 2004, respectively. Overall, insensitive isolates were detected in 51% of the fields, and the proportions of insensitive isolates were 8.1, 20.7, and 18.3% in 2002, 2003, and 2004, respectively. The aggressiveness of 10 insensitive and 18 sensitive isolates and the efficacy of iprodione was tested in planta. Onion leaves were inoculated with 750 μl of a conidial suspension of 75,000 conidia per ml and incubated in a growth chamber at 15°C. Aggressiveness was measured as lesion density (average number of lesions per cm2 of onion leaf). Lesion density varied from 2.82 to 8.04 lesions per cm2 of leaf. There was a significant effect (P < 0.0001) of isolates on lesion density. However, there was no significant correlation between lesion density and sensitivity to iprodione (r = 0.08). When onion leaves were sprayed with 1,875, 3,750, and 7,500 ppm of iprodione, percent inhibition of lesion density was higher for sensitive isolates with means of 43.04, 61.42, and 74.59, respectively. Accordingly, percent inhibition was lower for insensitive isolates with means of 13.81, 28.26, and 44.37 for iprodione concentrations of 1,875, 3,750, and 7,500, respectively. It was concluded that the incidence of insensitive isolates was relatively low, but insensitive isolates were capable of infecting onion leaves. There was a good relationship between insensitivity to iprodione in B. squamosa populations measured in vitro with the AQ method, and the reduced efficacy of iprodione in controlling Botrytis leaf blight.

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First Report of a 16SrII-A Subgroup Phytoplasma Associated with Purple Coneflower (Echinacea purpurea) Witches'-Broom Disease in Taiwan

Plant Disease ◽

10.1094/pdis-10-11-0888 ◽

2012 ◽

Vol 96 (4) ◽

pp. 582-582 ◽

Cited By ~ 8

Author(s):

Y.-W. Tseng ◽

W.-L. Deng ◽

C.-J. Chang ◽

C.-C. Su ◽

C.-L. Chen ◽

...

Keyword(s):

Medicinal Plant ◽

Nested Pcr ◽

Echinacea Purpurea ◽

Flowering Plant ◽

Diseased Plant ◽

Universal Primer ◽

Tissue Samples ◽

First Report ◽

Rdna Sequences ◽

Purple Coneflower

Purple coneflower (Echinacea purpurea), widely grown as an ornamental and medicinal plant, is a perennial flowering plant that is native to eastern North America. In July 2011, symptoms indicative of phytoplasma disease, including floral virescence, phyllody, and witches'-broom (WB), were observed to be affecting plants in coneflower fields in Wufeng, Taichung City, Taiwan. Incidence of infected plants was estimated to be greater than 90% within a single field. Phytoplasmas previously associated with purple coneflower WB disease have all been classified as aster yellows group (16SrI) strains (GenBank Accession Nos. EU333395, AY394856, EU416172, and EF546778) except for pale purple coneflower (Echinacea pallida) WB in Australia, which was identified as a subgroup 16SrII-D member (2). Three diseased plants were uprooted and transplanted in a greenhouse for further study. Transmission electron microscopy revealed clusters of phytoplasma cells ranging from 170 to 490 nm in diameter in phloem sieve elements of virescent and phylloid flowers and stems from diseased plants. Comparable tissues from symptomless plants were devoid of phytoplasma. Total DNA was extracted from plant tissue samples (50 to 100 mg each) including stems, leaves, and flowers by a modified CTAB method (1) from three symptomatic plants as well as from three asymptomatic coneflower plants seedlings. Analyses by a nested PCR using universal primer pairs P1/P7 followed by R16F2n/R16R2 were performed to detect putative phytoplasma (2). Each primer pair amplified a single PCR product of either 1.8 or 1.2 kb, respectively, from diseased plant tissues only. The nested PCR products (1.2 kb) amplified from phylloid flowers of the three diseased plants were cloned separately and sequenced (GenBank Accession Nos. JN885460, JN885461, and JN885462). Blast analysis of the sequences revealed a 99.7 to 99.8% sequence identity with those of Echinacea WB phytoplasma strain EWB5 and EWB6 (GenBank Accession Nos. JF340076 and JF340080), which reportedly belonged to the 16SrII-D subgroup (2). Moreover, iPhyClassifier software (3) was used to perform sequence comparison and generate the virtual restriction fragment length polymorphism (RFLP) profile. The 16S rDNA sequences share a 99.4 to 99.5% similarity with that of the ‘Candidatus Phytoplasma australasiae’ reference strain (Y10097) and the RFLP patterns are identical to that of the 16SrII-A subgroup. Taken together, these results indicated that the phytoplasma infecting purple coneflower in Taiwan is a ‘Ca. Phytoplasma australasiae’-related strain and belongs to the 16SrII-A subgroup. To our knowledge, this is the first report of a 16SrII-A subgroup phytoplasma causing WB disease on purple coneflower in Taiwan. The occurrence of phytoplasma on purple coneflower could have direct implication for the economically important ornamental, medicinal plant, and floral industry in Taiwan, especially to the growers and breeders that eagerly promote the purple coneflower industry. References: (1) T. M. Fulton et al. Plant Mol. Biol. Rep. 13:207, 1995. (2) T. L. Pearce et al. Plant Dis. 95:773, 2011. (3) Y. Zhao et al. Int. J. Syst. Evol. Microbiol. 59:2582, 2009.

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First Report of Mefenoxam Sensitivity and Pathogenicity of Phytophthora citricola Isolated from American Ginseng (Panax quinquefolium)

Plant Disease ◽

10.1094/pdis-92-12-1706a ◽

2008 ◽

Vol 92 (12) ◽

pp. 1706-1706

Author(s):

S. N. Hill ◽

O. P. Hurtado-Gonzales ◽

K. H. Lamour ◽

M. K. Hausbeck

Keyword(s):

Block Design ◽

Silica Sand ◽

Distilled Water ◽

Panax Quinquefolium ◽

Damping Off ◽

Tissue Samples ◽

First Report ◽

Zoospore Release ◽

Fluorescent Lighting

In March of 2004, stratified ginseng seeds from commercial Wisconsin gardens were planted in sterilized silica sand in a research greenhouse at Michigan State University. Following emergence, seedlings exhibiting wilting, damping off, and black stem lesions were observed. In the laboratory, symptomatic seedlings were rinsed with distilled water. Tissue samples were excised and embedded in water agar amended with ampicillin (100 mg/liter) and incubated at 25°C. In addition to the isolation of Phytophthora cactorum, a known pathogen of ginseng, P. citricola, (five isolates) also was identified from single-zoospore cultures based on morphology (2). One-week-old, dilute V8 agar cultures were used to obtain single zoospores. Cultures were flooded with 20 ml of sterilized distilled water chilled to 10°C and incubated at 25°C for 25 min to induce zoospore release. Zoospore suspensions were spread onto water agar plates, and after 24 h at 25°C, single germinating zoospores were selected at random and transferred to benomyl, ampicillin, rifampicin, and pentachloronitrobenzene (BARP)-amended V8 agar plates. Sequence analysis of the internal transcribed spacer (ITS) region 1 and 2 of the rDNA was also used to distinguish P. citricola from P. cactorum. A representative sequence for the isolates of P. citricola (NCBI Accession No. FJ217388) matched (100% similarity) a P. citricola isolate deposited in GenBank (Accession No. DQ486661). To screen P. citricola for in vitro response to mefenoxam, agar plugs (7-mm diameter) from 1-week-old V8 agar cultures incubated at 25°C under fluorescent lighting were placed in the center of each of two V8 agar plates amended with 0 and 100 ppm of mefenoxam (Ridomil Gold EC, 48% a.i., suspended in sterile distilled water and added to V8 agar cooled to 49°C). The plates were incubated at 25°C for 3 days under fluorescent lighting. Isolates were assigned a mefenoxam sensitivity rating based on the percentage of radial mycelial growth on the amended V8 agar when compared with the unamended control. Each of the five isolates was scored as mefenoxam resistant with growth on 100-ppm plates >30% of the controls. Koch's postulates were conducted for the isolates of P. citricola recovered from ginseng seedlings to confirm pathogenicity. Previously, P. citricola was reported as nonpathogenic to ginseng (1). Three-week-old, healthy ginseng seedlings were planted into 89- × 64-mm pots filled with autoclaved medium-particle vermiculite and maintained in the greenhouse under 63% shade cloth with temperatures between 18 and 26°C. Pots were arranged in a completely randomized block design with eight seedlings per isolate as replicates and watered as needed. A 2-ml inoculum suspension (approximately 104 zoospores) was injected into the potting medium at the stem base of each seedling. All of the isolates were pathogenic to ginseng seedlings with 60% of inoculated seedlings per isolate exhibiting wilting, damping off, and blackened stems within 3 weeks after inoculation. P. citricola was reisolated from all inoculated plants. To our knowledge, this is the first report of P. citricola pathogenic on ginseng. References: (1) T. W. Darmono et al. Plant Dis. 75:610, 1991. (2) D. C. Erwin and O. K. Ribeiro. Page 96 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN. 1996.

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First Report of Volutella Blight on Pachysandra Caused by Volutella pachysandricola in China

Plant Disease ◽

10.1094/pdis-11-11-0997 ◽

2012 ◽

Vol 96 (4) ◽

pp. 584-584

Author(s):

Q. Bai ◽

Y. Xie ◽

R. Dong ◽

J. Gao ◽

Y. Li

Keyword(s):

Morphological Characteristics ◽

Stem Canker ◽

Botanical Garden ◽

The United States ◽

Culture Collection ◽

Leaf Blight ◽

Conidial Suspension ◽

First Report ◽

Leaf Spots ◽

Plastic Bags

Pachysandra (Pachysandra terminalis, Buxaceae) and Japanese Pachysandra, also called Japanese Spurge, is a woody ornamental groundcover plant distributed mostly in Zhejiang, Guizhou, Henan, Hubei, Sichuan, Shanxi, and Gansu provinces in China. In April 2010, P. terminalis asymptomatic plants were shipped from Beijing Botanical Garden Institute of Botany Chinese Academy of Science to the garden nursery of Jilin Agricultural University (43°48′N, 125°23′E), Jilin Province. In June 2011, Volutella blight (sometimes called leaf blight and stem canker) of P. terminalis was observed on these plants. Infected leaves showed circular or irregular, tan-to-brown spots often with concentric rings and dark margins. The spots eventually grew and coalesced until the entire leaf died. Cankers appeared as greenish brown and water-soaked diseased areas, subsequently turning brown or black, and shriveled and often girdled the stems and stolons. During wet, humid weather in autumn, reddish orange, cushion-like fruiting structures of the fungus appeared on the stem cankers and undersides of leaf spots. Symptoms of the disease were consistent with previous descriptions (2–4). Five isolates were obtained from necrotic tissue of leaf spots and cankers of stems and stolons and cultured on potato dextrose agar. The colony surface was salmon colored and slimy. Conidia were hyaline, one celled, spindle shaped, and 12.57 to 22.23 × 3.33 to 4.15 μm with rounded ends. Morphological characteristics of the fungus were consistent with the description by Dodge (2), and the fungus was identified as Volutella pachysandricola (telemorph Pseudonectria pachysandricola). The internal transcribed spacer (ITS) regions of the nuclear rDNA were amplified using primers ITS4/ITS5 (1). The ITS sequences were 553 bp long and identical among these five isolates (GenBank Accession No. HE612114). They were 100% identical to Pseudonectria pachysandricola voucher KUS-F25663 (Accession No. JN797821) and 99% identical to P. pachysandricola culture-collection DAOM (Accession No. HQ897807). Pathogenicity was confirmed by spraying leaves of clonally propagated cuttings of P. terminalis with a conidial suspension (1 × 106 conidia/ml) of the isolated V. pachysandricola. Control leaves were sprayed with sterile water. Plants were covered with plastic bags and kept in a greenhouse at 20 to 25°C for 72 h. After 5 to 8 days, typical disease symptoms appeared on leaves, while the control plants remained healthy. V. pachysandricola was reisolated from the leaf spots of inoculated plants. Pachysandra leaf blight and stem canker also called Volutella blight, is the most destructive disease of P. terminalis and previously reported in the northern humid areas of the United States (Illinois, Connecticut, Ohio, Indiana, Iowa, Massachusetts, Missouri, Kentucky, and Wisconsin), northern Europe (Britain, Germany, and Poland), and the Czech Republic. To our knowledge, this is the first report of the disease caused by V. pachysandricola in China. The disease may become a more significant problem in P. terminalis cultivation areas if the disease spreads on P. terminalis in nursery beds. References: (1) D. E. L. Cooke et al. Mycol. Res. 101:667, 1997. (2) B. O. Dodge. Mycologia 36:532, 1944. (3) S. M. Douglas. Online publication. Volutella Blight of Pachysandra. The Connecticut Agricultural Experiment Station, 2008. (4) I. Safrankova. Plant Protect. Sci.43:10, 2007.

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First Report of Phoma strasseri as a Pathogen of Stachys officinalis in Bulgaria

Plant Disease ◽

10.1094/pdis.2002.86.6.699b ◽

2002 ◽

Vol 86 (6) ◽

pp. 699-699

Author(s):

S. G. Bobev ◽

A. F. Margina ◽

J. de Gruyter

Keyword(s):

Plant Protection ◽

Aerial Mycelium ◽

Culture Collection ◽

Leaf Spot Disease ◽

Oatmeal Agar ◽

First Report ◽

Average Temperature ◽

Leaf Spots ◽

Monarda Didyma

For several years, a leaf spot disease has been observed on Betony, Stachys officinalis (synonym Betonica officinalis), in an experimental field in Kazanlak, Bulgaria. The round to somewhat angular spots (6 to 8 mm diameter) are dark brown with a pale center and have a chlorotic halo. A Phoma species isolated from the lesions formed regular to irregular, light brown colonies on potato dextrose agar (PDA). The isolate was studied as described by de Gruyter and Noordeloos (2). After 7 days, the growth rate was 43 mm on oatmeal agar and 33 mm on malt agar; the colonies were olivaceous gray-to-glauceous gray with a regular outline and with finely floccose, white-to-olivaceous gray aerial mycelium. Pycnidia, produced after 2 weeks, were ostiolate, globose to subglobose, 120 to 280 μm in diameter, citrine or honey, and later olivaceous to olivaceous black. The conidiogenous cells were globose to bottle shaped, 2 to 6 × 3 to 5 μm. The conidia were hyaline and unicellular, 5 to 7.5 × 2.5 to 4.2 μm, cylindrical to ellipsoidal with several small, scattered guttules. Chlamydospores were absent. According to these in vitro characters and after comparing the isolate with several Phoma isolates present in the culture collection of the Dutch Plant Protection Service, Wageningen, the Netherlands, the fungus has been identified as Phoma strasseri Moesz. The pathogenicity of the isolate was confirmed by artificial leaf inoculation of potted S. officinalis plants with a spore suspension (8 × 106 spores per ml) kept in a moist chamber for 48 h at a mean average temperature of 16°C. Leaf spots observed 4 to 5 days after inoculation were similar to those observed in the field. P. strasseri was subsequently reisolated from the spots. P. strasseri (synonym Phoma mentae Strasser) has been recorded as the cause of rhizome and stem rot on mint, Mentha spp., in Europe, Japan, and North America (3). In addition, this fungus has been found in New Zealand (strain identified at the Dutch Plant Protection Service, unpublished data). To our knowledge, this is the first report of P. strasseri on S. officinalis in Bulgaria. P. strasseri may produce septate conidia and, therefore, can be classified in Phoma section Phyllostictoides Zherbele ex Boerema (1). P. strasseri clearly differs from other Phoma species described on Lamiaceae: Phoma leonuri Letendre (Phoma section Plenodomus (Preuss) Boerema et al., pycnidia scleroplectenchymatous, conidia aseptate, 3.5 to 5.5 × 1.5 to 2.5 μm), Phoma dorenboschii Noordel. & de Gruyter (Phoma Sacc. section Phoma, conidia aseptate, 3 to 5.5 × 2 to 2.5 μm, producing dendritic crystals in vitro), and Phoma valerianae Henn. (Phoma Sacc. section Phoma, conidia aseptate, 2.5 to 4 × 1.5 to 2 μm). Occasionally P. strasseri has been isolated from other Lamiaceae, namely Monarda didyma (Dutch Plant Protection Service, unpublished data). There is also a report from Valeriana sp. (3). References: (1) G. H. Boerema. Mycotaxon 64:321, 1998. (2) J. de Gruyter and M. E. Noordeloos. Persoonia 15(1):71, 1992. (3) C. E. Horner. Plant Dis. Rep. 55:814, 1971.

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First Report of Phytophthora tropicalis on Rhododendron in Italy

Plant Disease ◽

10.1094/pdis-04-13-0445-pdn ◽

2013 ◽

Vol 97 (10) ◽

pp. 1385-1385 ◽

Cited By ~ 2

Author(s):

L. Luongo ◽

M. Galli ◽

S. Vitale ◽

A. Haegi ◽

A. Belisario

Keyword(s):

Late Summer ◽

Selective Medium ◽

Phytophthora Species ◽

Width Ratio ◽

Broad Host Range ◽

In Planta ◽

First Report ◽

European Nucleotide Archive ◽

Pure Cultures

The genus Rhododendron comprises over 1,000 species, which represent many important ornamental shrubs. Microbial isolations were made from Rhododendron catawbiense plants showing symptoms of wilt, dieback, and death of shoots obtained from two nurseries in the Latium region in the late summer of 2012. A Phytophthora species was consistently recovered by plating small pieces of stem and collar tissues, cut from the margin of lesions, on P5ARPH selective medium. Pure cultures were obtained by single-hyphal transfers and they grew in a rosaceous pattern on potato dextrose agar (PDA) at an optimum temperature of 28 to 30°C. Sporangia formation was induced on pepper seeds (3). Sporangia were ellipsoid, fusiform or obpyriform, papillate, occasionally bipapillate, caducous, with a long pedicel (up to 100 μm), and mean dimensions of 45 × 25 μm with a mean length/width ratio of 1.8. Chlamydospores ranged from 25 to 32 μm in diameter. Isolates were considered heterothallic because they did not produce gametangia in vitro or in planta. On the basis of morphological features, the isolates were identified as Phytophthora tropicalis Aragaki & Uchida. Identity was confirmed by sequence comparison in GenBank with 99% homology both for internal transcribed spacer (ITS) and mitochondrial partial COI for cytochrome oxidase subunit 1. The sequences of two isolates AB211 and AB212 were deposited in the European Nucleotide Archive (ENA) with accession nos. HF937577 and HF937578 for ITS, and HF937579 and HF937580 for COI, respectively. Pathogenicity tests were conducted in the greenhouse on a total of six 1-year-old shoots cut from R. catawbiense plants with two inoculation points each. Mycelial plugs cut from the margins of actively growing 8-day-old cultures on PDA were inserted through the epidermis to the phloem. Controls were treated as described above except for inoculation with sterile PDA plugs. Inoculated shoots were incubated in test tubes with sterile water for 1 week in the dark at 26 ± 2°C. Lesions were evident at the inoculation points. P. tropicalis was consistently reisolated from the margin of symptomatic tissues. Control shoots remained symptomless. In Italy, P. tropicalis has been reported on several ornamental species (1) and on apricot trees (4) indicating a broad host range. On the same host it has been reported in Virginia, United States (2). To the best of our knowledge, this is the first report of Phytophthora damage on Rhododendron caused by P. tropicalis in Italy. References: (1) S. O. Cacciola et al. Plant Dis. 90: 680, 2006. (2) C. X. Hong et al. Plant Dis. 90: 525, 2006. (3) E. Ilieva et al. Eur. J. Plant Path. 101: 623, 1995. (4) A. Pane et al. Plant Dis. 93: 844, 2009.

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First Report of Phytophthora Blossom Blight of Chrysanthemum Caused by Phytophthora nicotianae

Plant Disease ◽

10.1094/pdis.2001.85.8.923b ◽

2001 ◽

Vol 85 (8) ◽

pp. 923-923 ◽

Cited By ~ 2

Author(s):

J. M. Mullen ◽

A. K. Hagan ◽

D. K. Carey

Keyword(s):

Chrysanthemum Morifolium ◽

Selective Medium ◽

Leaf Blight ◽

Phytophthora Nicotianae ◽

Mycelium Growth ◽

First Report ◽

Dendranthema Grandiflorum ◽

Potted Plants ◽

Plastic Bags ◽

Growth Room

In October 2000, chrysanthemums (Dendranthema × grandiflorum) cv. Debonair exhibiting blossom blight were submitted to the Plant Diagnostic Lab at Auburn University by a commercial greenhouse where most of the potted plants of this cultivar were symptomatic. At a local retail outlet, approximately 95% of the plants of the same cultivar of chrysanthemum had a similar blossom blight. Blighted petals were examined microscopically, and nonpapillate, internally proliferating sporangia (40 to 45 μm in length), characteristic of some species of Phytophthora, were observed. A species of Phytophthora was isolated repeatedly on PARP selective medium (corn meal agar containing pimaricin, ampicillin, rifamycin, and pentachloronitrobenzene). Isolates recovered were grown on V8 juice agar, under fluorescent lights and in darkness, at room temperature. These isolates were identified as Phytophthora nicotianae (= Phytophthora parasitica), on the basis of morphological and cultural characteristics. Sporangia were papillate (including some with dual apices), noncaducous, 45 to 60 μm in length, and spherical, ovoid, or obpyriform. Mycelium growth occurred at 36°C. Isolates were considered heterothallic because they did not produce oospores when grown on V8 juice agar in the dark for 2 weeks. Sporangia that were nonpapillate and proliferating internally were not observed on any of these isolates. Because we apparently did not isolate the Phytophthora spp. seen microscopically on petals, we cannot comment on its exact identity or significance in causing this disease. We did conduct pathogenicity tests to determine whether isolates of P. nicotianae were capable of causing the observed symptoms. These tests were conducted twice on chrysanthemum cultivars Debonair, Yellow Triumph, Spotlight, Raquel, Jennifer, Grace, and Hot Salsa. In the first test, two plants of each cultivar were sprayed to runoff with a zoospore suspension (105 spores per ml) in sterile, filtered water. Two plants of each cultivar were sprayed with sterile, filtered water as noninoculated controls. Individual plants were placed in loosely closed plastic bags, misted daily, and held at 23 to 24°C with indirect lighting (approximately 12 h per day) for 1 week. In the second test, four plants of each cultivar except Debonair were inoculated as described previously, four plants of each cultivar were left untreated as noninoculated controls, and one Debonair plant was inoculated and one remained noninoculated. Plants were held for 3 days in an environmentally controlled growth room, with 23°C days (11 h)-20°C nights (13 h), under a plastic tent where high levels of humidity were maintained with a humidifier and daily misting. A grow light provided a low level of lighting (4 to 6 μE · m-2 · s-1). All inoculated plants developed severe blossom blight similar to that observed initially. In the first test, symptoms were evident at 2 days. In the growth room, blossom blight first was observed at 24 h postinoculation. In both tests, blossom blight severity increased quickly in the 1 to 2 days after the initial occurrence of symptoms. Only blossoms became diseased; symptoms did not extend to other plant organs. P. nicotianae was reisolated consistently from symptomatic blossoms on selective medium. This is, we believe, the first report of blossom blight on chrysanthemum caused by a species of Phytophthora. Previously, P. nicotianae has been reported to cause leaf blight on artificially inoculated Chrysanthemum × morifolium (Dendranthema × grandiflorum) cultivars Capri and Vermilion in Florida (1) and twig and leaf blight on Chrysanthemum coronarium in India (2). References: (1) C. R. Semer and B. C. Raju. Plant Dis. 69:1005–1006, 1985. (2) N. Sushma and N. D. Sharma. J. Mycol. Plant Pathol. 27:345, 1997.

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First Report of Aristastoma Leaf Spot on Desert Rose

Plant Disease ◽

10.1094/pdis.1997.81.8.960d ◽

1997 ◽

Vol 81 (8) ◽

pp. 960-960 ◽

Cited By ~ 1

Author(s):

R. T. McMillan ◽

W. R. Graves ◽

R. M. Leahy

Keyword(s):

Diseased Plant ◽

Dade County ◽

Conidial Suspension ◽

First Report ◽

Leaf Spots ◽

Foliar Symptoms ◽

Spraying Plants ◽

International Mycological Institute

In the spring of 1995, a species of Aristastoma was isolated from foliar lesions of Adenium obesum that originated in a commercial nursery in Dade County, FL, where 100% of the crop was affected. Plant foliage had irregular, oval to circular, rusty brown, necrotic lesions 5 to 15 mm in diameter. Large leaf spots developed tan centers. An undescribed species of Aristastoma was isolated consistently from symptomatic plant material. The identity of the fungus was confirmed by the International Mycological Institute, Egham, England. Both in vivo and in vitro, the fungus has immersed mycelium, pale brown to hyaline, branched and septate. Pycnidia are 160 to 300 μm in diameter with prominent setae 75 to 125 μm surrounding the ostiole, with hyaline, 1 septate, conidia that are 25 to 30 × 3 to 4 μm. Pathogenicity was tested on shadehouse-grown, 8-month-old desert rose plants by spraying plants with a conidial suspension containing 104 conidia per ml. Inoculated plants developed foliar symptoms within 5 to 10 days that were consistent with those originally observed on the diseased plant samples. The pathogen was isolated from symptomatic tissue of inoculated plants. Species of Aristastoma are reported to cause foliar symptoms mostly on leguminous crops, and in Florida Aristastoma oeconomicum causes lesions on Vigna. This is the first report of this or any species of Aristastoma on Adenium obesum or any other member of the Apocynaceae.

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First Report of Rhizoctonia solani Subgroup AG 1-ID Causing Leaf Blight on Durian in Vietnam

Plant Disease ◽

10.1094/pdis-92-4-0648b ◽

2008 ◽

Vol 92 (4) ◽

pp. 648-648 ◽

Cited By ~ 1

Author(s):

T. T. M. Thuan ◽

N. Tho ◽

B. C. Tuyen

Keyword(s):

Rhizoctonia Solani ◽

Sequence Similarity ◽

Its Region ◽

The Philippines ◽

Leaf Blight ◽

First Report ◽

Rdna Its ◽

Durio Zibethinus ◽

Leaf Spots ◽

Irregular Border

During the rainy season in Vietnam, leaf blight disease caused by Rhizoctonia solani often occurs on 3- to 5-year-old durian (Durio zibethinus). Symptoms appear as large, pale brown, blighted lesions with an irregular border. In excessive moisture conditions, yellowish white hyphae appear on the lesions, and the affected leaves turn dark brown and wilt. There are no reports describing the anastomosis groups (AG) and subgroups of Rhizoctonia solani occurring in durian. In June of 2004, two isolates of R. solani were obtained from leaf blight lesions on durian growing in Binh Duong and Dong Nai provinces. The durian isolates were identified as AG 1 based on hyphal anastomosis. In pathogenicity tests, the durian isolates infected cucumber, mung bean, and leaf mustard seedlings grown on water agar in petri dishes. The rDNA-ITS sequence of the durian isolates was determined (GenBank Accession Nos. EF197797 and EF197798) and aligned with those of AG 1-IA, AG 1-IB, AG 1-IC, and AG 1-ID available in the GenBank database. The sequence similarity of the total rDNA-ITS region (including 5.8S) within the durian isolates was 99.9%. The sequence similarity of the durian isolates and AG 1-ID isolates was 99.1 to 100%, but similarity with other AG 1 subgroups was 89.1 to 94.0%. The results suggest that the two Vietnam durian isolates of R. solani are members of AG 1-ID. AG 1-ID has only been reported causing necrotic leaf spots on coffees in the Philippines (1). To our knowledge, this is the first report of R. solani AG 1-ID on durian and the first report of the presence of R. solani AG 1-ID in Vietnam. Reference: (1) A. Priyatmojo et al. Phytopathology 91:1054, 2001.

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