First Report of Leaf Rot Caused by Fusarium oxysporum and Pythium aphanidermatum on Aechmea fasciata in Hainan Province, China.

Aechmea fasciata is a bromeliad that is propagated by tissue culture as an ornamental plant. A high percentage (25 to 55%) of 1- to 5-month-old seedlings were found decayed in nursery gardens that have been established in recent years in Hainan Province, People's Republic of China. There were two types of symptoms: (i) in yellow rot, the decay appears first in the new leaf apex as a water-soaked, yellow lesion, and the lesion spreads from the leaf apex to the leaf base until the whole leaf becomes water soaked and yellow; and (ii) in brown rot, decay occurs first at the base of older leaves. The lesion is water soaked but later becomes brown, and the lesions develop from leaf base to leaf apex and spread to adjacent leaves. Eventually the whole plant is rotted, but the decay remains brown. Both types of symptoms on A. fasciata have not been reported in China. Fusarium sp. was isolated from the yellow rot type lesions, and Pythium sp. was isolated from the brown rot type lesions. Isolates of Fusarium and Pythium spp. were inoculated on wounded and unwounded healthy plants. Yellow rot type and brown rot type lesions were observed on wounded host three days after inoculation with the respective pathogen. No lesions were observed on unwounded inoculated plants or on wounded and unwounded control plants. The same Fusarium and Pythium spp. were reisolated from the yellow and brown rot type lesions, respectively, in inoculated plants, thus fulfilling Koch's postulates. Colonies of the Fusarium sp. were white on potato dextrose agar, purple on rice medium, and first yellow, and then blue green in 4 days on selective carrot medium. On carnation media, microconidia were abundant, 1- to 2-celled, oval- to kidney-shaped, and 2.4 to 3.6 × 4.8 to 7.2 μm. Macroconidia were rare, sickle-shaped with attenuated apical cells and foot-shaped basal cells. Chlamydospores were also abundant, globose, formed singly or in pairs, and intercalary or on short lateral branches. This pathogen was identified as Fusarium oxysporum based on these characteristics (1,3). The Pythium sp. on potato dextrose agar was white and cottony. On selective carrot medium, hyphae were 3.6 to 7.5 μm in diameter. Sporangia had irregular swellings and were acrogenous. Oogonia were globose, colorless, acrogenous or intercalary, 14.8 to 27.6 μm in diameter. Antheridia were copulated with oogonia in its apex or lateral. Oospores were spherical, aplerotic, and 13.2 to 25.2 μm in diameter. This pathogen was identified as Pythium aphanidermatum based on these characters (2). To our knowledge, this is first report of leaf rot caused by F. oxysporum and P. aphanidermatum on A. fasciata in the People's Republic of China. References: (1) C. Booth. The Genus Fusarium. The Eastern Press, London, 1971. (2) W. Jingchao. Pages 30-32 in: Manual of Fungi Identification. The Shanghai Science Technology Press, 1979. (3) P. E. Nelson et al. Fusarium Species-An Illustrated Manual of Identification. The Pennsylvania State University Press University Park, 1976.