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First Report of Fusarium oxysporum Causing Soft Fruit Rot Disease of Gray Jujube (Zizyphus jujuba) in China

Gray Jujube, Zizyphus jujuba Mill., is a fruit crop unique to China that produces small fruit of high nutritional value with potential health benefits (2). In mid-September 2011, a fruit rot affecting approximately 10% of gray jujube fruit was observed in Xinzheng Date Garden, Henan Province, China. The diseased fruits exhibited small, oval, pale reddish brown lesions that expanded into clear concentric rings. Over time, the superficial lesions developed into soft rot affecting the whole fruit that produced a pungent odor. A putative Fusarium sp. was isolated by a single spore isolations from conidiophores produced on the decaying fruit. The isolated colonies first appeared on potato dextrose agar (PDA) as white to light yellow, then turned light pink. Falciform macroconidia were produced on PDA and were straight to slightly curved, usually 3-septate, short or medium long, 15.0 to 28 × 2.5 to 4.0 μm, with a curved apical cell and foot shaped to pointed basal cell. Microconidia were produced in false heads on Synthetic Nutrient-poor Agar (SNA), and were oval, 0-septate, 5.0 to 9.5 × 1.5 to 2.8 μm. Phialides were cylindrical and ranged from 7.0 to 20.0 × 0.7 to 1.4 μm. Chlamydospores were produced singularly and in pairs (1). Pathogenicity of the putative Fusarium sp. was evaluated by surface-sterilizing fresh gray jujubes on a healthy tree field and inoculating by placing a mycelial plug of the Fusarium sp. culture in contact with the fruit. An equal number of fresh gray jujube fruits were placed in contact with non-colonized PDA plugs to serve as a control. Each jujube fruit was wounded three times to create three holes close together using a steel needle (0.5 mm diameter), before inoculation with an agar plug. All the branches with inoculated fruits were enclosed in a clear plastic bag to maintain humidity and prevent cross contamination. After 3 days, inoculated jujubes exhibited the similar symptoms to those originally observed on the naturally infected fruits. Colonies resembling the Fusarium sp. isolated from the original lesions were obtained from each of the symptomatic fruits. Fruit inoculated with un-colonized PDA plugs remained asymptomatic and no fungus was isolated from these fruit. Koch's postulates were repeated three times with the same results. Based on the morphological characteristics, the Fusarium sp. was identified as F. oxysporum (1). The identity of the isolate was confirmed to be F. oxysporum by DNA sequencing of the elongation factor 1-alpha (EF-1a) gene (GenBank Accession No. KC796007), which was 99% homologous to those of other F. oxysporum isolates (JF430187 and JF430188). To our knowledge, this is the first report of F. oxysporum causing soft rot in fresh gray jujubes in Henan. This disease affects the yield and quality of fresh gray jujubes and potentially may threaten the jujube industry.

References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual, 2006. (2) J. Sheng et al. Acta Hortic. 620:203, 2003.