Pseudocercospora ixoricola Causing Leaf Spots on Ixora coccinea in Brazil

Abstract

Ixora coccinea, known as jungle geranium, flame of the woods, or flame of the forest, is a shrub in the Rubiaceae native to Eastern India and is widely cultivated for its showy red globose inflorescences. It was introduced in Brazil in the beginning of the 19th century where it became a popular ornamental (2). Recently, leaf spots were observed on I. coccinea foliage in Brazil. Severely diseased plants were unsightly with loss of foliage and remaining foliage was heavily spotted and yellowed. Sparse colonies of a fungus were consistently observed to be associated with diseased tissues. Slides were prepared by scraping colonized surfaces with a scalpel and mounting the fungal structures in lactophenol. Observations, measurements, and photographs were prepared with a light microscope (Olympus BX 50). The fungus was isolated in pure culture in plates containing V8 juice agar and incubated at 25°C. Pathogenicity was verified by placing pure culture plugs, obtained from actively growing colonies, onto healthy leaves of I. coccinea still attached to living plants left in a dew chamber. After 48 h, plants were removed and transferred to a greenhouse. Controls consisted of leaves of two separate healthy plants on which sterile culture medium plugs were deposited. Typical leaf spot symptoms appeared 11 days after inoculation and sporulation was observed after 30 days, but was not observed on the controls. Lesions on leaves were subcircular to polygonal or irregular, reddish brown to dark brown, 3.5 to 12 mm in diameter, coalescing, and leading to premature abscission. Fungus morphology was as follows: stromata absent; sporulation nearly indistinct under the dissecting microscope; conidiophores hypophyllous, either emerging from the stomata in small fascicles or isolate and formed from external mycelium, obclavate to cylindrical, 15 to 60 × 3.0 to 6.0 μm, 3 to 7 septate, obliquely constricted at septae, simple or branched, thin walled, brown, smooth; conidiogenous loci inconspicuous, not darkened, unthickened; conidia obclavate to cylindrical, straight to slightly curved, 17.5 to 89.0 × 3.0 to 5.0 μm, apex obtuse, base obconic-truncate, 1 to 7 obliquely septate, subhyaline, thin walled, eguttulate, smooth. Except for minor differences on conidiophore and conidial length, morphology was as described for Pseudocercospora ixoricola (4). Representative samples collected in the states of Minas Gerais (VIC 31216 - May 2009) and Rio de Janeiro (VIC 31217 - July 2009) were deposited in the local herbarium. Additional ad hoc observations indicate a widespread distribution of this disease in southeastern Brazil. Until now the sole cercosporoid fungus recorded on I. coccinea was P. ixorae from Asia and North America. There is also a record of this fungal species from an Ixora sp. from Brazil (1). Features such as the absence of stromata and the shape and size of conidiophores and conidia, separates it readily from P. ixoricola and P. ixoriana (a third species of Pseudocercospora known to be associated with plants in the genus Ixora). To our knowledge, this is the first record of P. ixoricola in South America and the first time it is recorded as a pathogen of I. coccinea. Previously, this fungus was only known in association with I. javanica in Singapore (3). References: (1) U. Braun and F. C. O. Freire. Cryptogam. Mycol. 23:295, 2002. (2) D. Hottz et al. Rev. Bras. Biociências, 5:642, 2007. (3) J. M. Yen. Rev. Mycol. 31:109, 1966. (4) J. M. Yen and G. Lim. Gard. Bull. Singap. 33:151, 1980.