First Report of Fusarium mangiferae Causing Mango Malformation in China.

Mango (Mangifera indica L.) malformation caused by Fusarium mangiferae has been reported in many mango-growing regions of the world (3). The disease was also observed in Yunnan and Sichuan provinces of China (1). Typical symptoms in seedlings included loss of apical dominance, hyperplasia and hypertrophy of vegetative buds, shortened internodes, and leaves that were more brittle than those of healthy plants. Inflorescences were abnormally branched and thickened, with panicles producing as much as two to five times the normal number of flowers. Flowers in the malformed inflorescence were much more enlarged and crowded than the generally hypertrophied axes of the panicle, thus producing no fruit or aborting early. To identify the pathogen, samples of malformed and healthy mango seedlings were collected from the affected plantings. For isolation, portions of stems were cut into 3- to 4-mm segments, surface disinfested, dried, and then plated on potato dextrose agar and incubated at 25°C. Within 5 days, white, fluffy, aerial mycelium developed. With the aid of an inverted microscope, single conidia were transferred to carnation leaf agar (CLA) medium. After 10 days of incubation, morphological characteristics were found to be identical to those of F. mangiferae (4). Aerial mycelium was white with no pigmentation observed on potato sucrose agar. Pigmentation on rice medium was pink. On CLA medium, conidia grew in branched conidiophores with false heads bearing monophialides or polyphialides. No conidiospores in chains were observed. Microconidia were ovate to long and oval, 0 to 1 septate, and 3.1 to 10.2 × 1.5 to 2.2 μm. Macroconidia are falculate, 3 to 5 septate, and 18 to 38 × 1.8 to 2.4 μm. Chlamydospores were not observed. Pathogenicity studies were conducted with 7-month-old asymptomatic mango seedlings. These seedlings, except for the controls, were inoculated by injection of the isolated fungus in the axillary or apical bud position. A 1-ml spore suspension (1 × 10⁶ spores/ml) was injected slowly into the stems using a microsyringe with three buds per seedling, for a total of 10 seedlings. Typical malformation symptoms developed within 3 to 4 months, and none of the plants inoculated with sterile water resulted in malformation symptoms. Reisolations from the induced malformed shoots yielded the same fungus, and no fungal growth was observed to be growing from the control plants. To confirm identity of the causal fungus, the gene encoding translation elongation factor 1 alpha (EF-1α) was amplified and sequenced (2). The EF-1α sequence was 660 bp long. The sequence (GenBank Accession No. HM068871) was 99.68% similar to sequences of FD_01167 in the Fusarium ID database. On the basis of symptoms, fungal morphology, the EF-1α region sequence, and pathogenicity testing, this fungus was identified as F. mangiferae. To our knowledge, this is the first report of F. mangiferae causing mango malformation in China. This report will establish a foundation for further study of F. mangiferae and effectively addressing the disease. References: (1) X. H. Chen. Pract. Technol. (in Chinese) 6:5, 1992. (2) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (3) J. Kumar et al. Annu. Rev. Phytopathol. 31:217, 1993. (4) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006.