Leaf spot on Clerodendrum x speciosus in Brazil caused by Pseudocercospora clerodendricola sp. nov.

Mancha foliar em Clerodendrum x speciosus no Brasil causada por Pseudocercospora clerodendricola sp. nov.

SHORT COMMUNICATION COMUNICAÇÃO

Leaf spot on Clerodendrum x speciosus in Brazil caused by Pseudocercospora clerodendricola sp. nov.

Mancha foliar em Clerodendrum x speciosus no Brasil causada por Pseudocercospora clerodendricola sp. nov.

Diogo Brito de Almeida; Davi Mesquita de Macedo; Robert W. Barreto

Departamento de Fitopatologia, Universidade Federal de Viçosa, 36570-000, Viçosa, MG, Brazil

ABSTRACT

Pseudocercospora clerodendricola sp. nov. is described herein. The fungus was found causing leaf spots in Clerodendrum x speciosum (bleeding heart) and its pathogenicity was demonstrated. Inoculation with culture discs placed on healthy leaves resulted in typical leaf spots appearing 30 days after inoculation.

Keywords: Cercosporoids, Mycosphaerellaceae, ornamental plant, plant pathology, taxonomy, Verbenaceae.

RESUMO

Uma nova espécie de fungo, Pseudocercospora clerodendricola é descrita em associação com Clerodendrum x speciosum (coração sangrento). Ela teve sua patogenicidade demonstrada pela inoculação de folhas sadias com discos de micélio. Manchas foliares equivalentes às observadas no campo foram produzidas 30 dias após a inoculação das plantas com discos de cultura.

Keywords: Cercosporoids, Mycosphaerellaceae, ornamental plant, plant pathology, taxonomy, Verbenaceae.

Studies on fungal pathogens of ornamental plants in Brazil have yielded numerous new disease records for Brazil (e.g.: Silva et al, 2006; Pereira et al. 2006; Ribeiro et al. 2006; Macedo & Barreto, 2008; Soares et al., 2009) and also novel fungal species such as Cordana versicolor Soares & R.W. Barreto (Soares et al., 2005) and Cercospora neomaricae Macedo & R.W. Barreto (Macedo & Barreto, 2008). Damage caused by such fungi varies from minor to very significant leading to losses in the commercial production of ornamentals or in the loss of their ornamental value through rendering infected plants unsightly.

Clerodendrum x speciosum Teijsm. & Binn. (Verbenaceae), is a hybrid between C. thomsoniae Balf. and C. splendens G. Don, which are from Africa. Several species belonging to Clerodendrum are widely used as ornamentals in Brazil, mostly to cover fences, gates and walls, because of their shrubby/scandent habit and attractive inflorescences (Lorenzi & Souza, 2001). There is little published information on pathogens of Clerodendrum worldwide (Farr et al., 2009; Mendes et al., 1998). In Brazil, besides three old records (Batista et al., 1964, 1967a, b), there is only a recent note on the occurrence of a fungal disease on a Clerodendrum: namely that of gray mold, Botrytis cinerea Pers. ex Fries, on Clerodendrum splendens (Macedo & Barreto, 2009). In January 2008, Clerodendrum x speciosum individuals bearing abundant leaf spots were found in a private garden in Viçosa, Minas Gerais, Brazil (Figure 1). A search through the literature yielded no record of that disease on Clerodendrum in Brazil or elsewhere. A study was then undertaken to clarify the etiology of this disease.

Specimens were collected, immediately brought to the lab and examined while still fresh. A fungus sporulating on diseased tissues was consistently associated with the leaf spots. Fungal structures were scraped with a scalpel from the infected tissues, mounted in lactophenol on glass slides and examined with a light microscope (Olympus BX 51) equipped with a digital camera (Olympus evolt E-330). The fungus was also isolated in VBA (vegetable broth-agar) (Pereira et al., 2003). A representative culture was deposited in the culture collection of the Universidade Federal de Viçosa (Coleção Micológica da Universidade Federal de Viçosa - CMUFV) under the provisional accession number DMM 75. Cultures were described based on observations of 19 day-old colonies on potato dextrose agar (PDA), malt extract agar (MEA) and vegetable broth agar (VBA) at 25°C, either under a 12-h light regime or under constant dark. Furthermore, the pathogenicity of the fungus was investigated. In this test two young Clerodendrum x speciosum plants around 20 cm tall were used. One plant was inoculated with culture disks obtained from the margin of an actively growing culture in VBA and placed on each side of three leaves. The other plant serving as control was treated the same way but only had sterile culture medium disks deposited on leaves. After inoculation, plants were covered with plastic bags with moist paper placed at the base of the plants in order to maintain high humidity. After 48 hours the plastic bags were removed and the plants were left in a greenhouse at 25 ± 2ºC and wetted twice a day. After a week plants were observed regularly for disease symptoms.

Pseudocercospora clerodendricola D.B. Almeida, D.M. Macedo & R.W. Barreto, sp. nov. MycoBank MB 516522 (Figure 2)

Etymology: based on the host genus Clerodendrum.

Differt a P. clerodendrigena laesio emmortus irregularis et halo luteos 0.4-1.2 mm longitudo et 0.3-2.7 mm latis; conidiophoris epigenous 15-23 longitudo et 3-6 μm latis; conidiis 74-103 x 3-4 μm, 5-11 septati. Differt a P. kashotoensis laesio; stromatibus 40-55 μm latis, conidiophoris numerosibus, etiam conidiophoriis epigenous et erumpens.

Holotype: BRAZIL, MINAS GERAIS: Viçosa. On living leaves of Clerodendrum x speciosum, 07 April 2008, D.M. Macedo (HOLOTYPE: VIC: 30734).

In folliis Clerodendrum x speciosum Teijsm. & Binn. (Verbenaceae).

Lesions on living leaves, starting as small chlorotic spots, becoming irregular, necrotic, dark brown to black with a yellow halo, 0.4-1.2 x 0.3-2.7 mm, coalescing and leading to blight of large areas of infected leaves; internal mycelium inter and intra-cellular, 3-5 μm diam, branched, septate, pale brown; stromata hypophyllous, erumpent, irregular to sub-globose, composed of pale to dark brown textura angularis, 15-50 x 40-55 μm diam.; conidiophores mostly reduced to short conidiogenous cells grouped over stromata in sporodochia, sub-cylindrical, 15-23 x 3-6 μm, 0-1 septate, smooth, pale brown; conidiogenous loci, often at attenuate apex of conidiogenous cells, 2. μm diam, not thickened, not darkened; conidia isolate, cylindrical to sub-cylindrical, 74-103 x 3-4 μm, base attenuated to a 1-3 μm diam truncate hilum not thickened, not darkened, 5-11 septate, guttulate, pale brown smooth.

In culture: colonies slow-growing (2.8-3.1 cm diam in 19 days); aerial mycelium ranging from smoke-gray to olivaceous-gray; colonies usually elevated centrally, of feltrose aerial mycelium, in VBA with a black rim of immersed mycelium at periphery; with diurnal zonation. In MEA with radiating immersed mycelium or corrugations at periphery, in PDA reverse dark gray with a black diffusate, sporulation absent.

Six cercosporoid taxa have been described in association with the genus Clerodendrum, namely: Cercospora apii s. lat. (originally described as C. volkameriae Speg. (according to Crous & Braun, 2003), Cercospora apii f sp. clerodendri Sorbes & Martinéz, Cercospora bakeri Syd., Passalora clerodendri (Goh & W.H. Hsieh) U. Braun & Crous, Pseudocercospora clerodendrii (J. Miyake) Deighton and P. kashotoensis (W. Yamam) Deighton (Crous & Braun, 2003; Farr et al., 2009). The new fungal species found on C. x speciosum clearly belongs to Pseudocercospora as it has the typical features delimiting this genus: specifically, conidiophores bearing unthickened and not darkened conidiogenous loci, and brown conidiophores and conidia (Crous & Braun, 2003). It is, therefore, clearly dissimilar to fungi in the Cercospora apii complex, as these have very long conidiophores (some being over 380 μm long) and long acicular conidia that are hyaline and have thickened and darkened hila (Crous & Braun, 2003). Although C. bakeri Syd. was regarded as having a doubtful taxonomic status and not belonging to Cercospora according to Crous & Braun (2003), it was described by Chupp (1953) as having significantly smaller conidia (30-60 x 4-6.5 μm) than those of P. clerodendricola. Passalora clerodendri was formerly placed in Mycovellosiella but recombined into Passalora by Braun & Crous (2003) for having the typical features for this genus, such as subhyaline to pigmented conidiophores and conidia and scars somewhat thickened and darkened. Features of conidial scars clearly separate the new species from members of Passalora. There are only two species of Pseudocercospora described in association with this plant genus: P. clerodendri [described as P. clerodendrigena by Braun (2002) and later treated as a synonym] and P. kashotoensis (W. Yamam) Deighton (Chupp, 1953; Yen et al., 1982). Conidiophores in P. kashotoensis are long-fasciculate (25-75 x 4-6 μm) and 2-7 septate instead of grouped in sporodochia and predominantly reduced to conidiogenous cells as in the new species. In P. clerodendri, the conidia are shorter and narrower (10.0-35.0 x 2.0-2.5 μm) (Braun, 2002). After 30 days of inoculation with P. clerodendricola, leaf spot symptoms identical to those seen in the field were observed on inoculated leaves but not on controls. The fungus was reisolated and formed colonies having a morphology equivalent to that described for P. clerodendricola.

ACKNOWLEDGMENTS

The authors would like to acknowledge financial support from the Conselho do Desenvolvimento Científico e Tecnológico - CNPq and Fundação de Amparo à Pesquisa de Minas Gerais - FAPEMIG.

Received 20 January 2010

Accepted 24 May 2010

Author for correspondence: Robert W. Barreto, e-mail: [e-mail]

TPP 10011

Section Editor: Marcos P.S. Câmara

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Publication Dates

• Publication in this collection
  09 Aug 2010
• Date of issue
  June 2010

History

• Accepted
  24 May 2010
• Received
  20 Jan 2010