Chinese jujube (Ziziphus jujuba Mill.) is widely planted in Xinjiang Province of China for fruit and as an effective herbal remedy. Wilt symptoms were observed on field-grown Z. jujuba during the spring and fall of 2010 and 2011. Diseased plants exhibited symptoms including wilted leaves, stunted growth, extensive brown discoloration on stems, and eventually death. In severe cases, approximately 60% of the plants in the field died. Repeated isolations from discolored stem vascular tissues were made on potato dextrose agar (PDA) after disinfestation in 1% HgCl2 for 1 min and dipping in 70% ethanol for 10 s. Petri dishes were then incubated in complete darkness at 26°C for 7 days. All colonies on PDA had pale pink-salmon-colored mycelia. Macroconidia were mostly three to five septate, slightly curved, and ranged from 2.9 to 11.9 × 29.5 to 45 μm. Microconidia were abundant, generally single celled, oval to kidney shaped, and ranged from 2.5 to 5 × 7.5 to 11.5 μm in false heads on short monophialides. Chlamydospores were single or in pairs and profusely distributed. These characteristics were similar to those of Fusarium oxysporum (2). The internal transcribed spacer (ITS) rDNA region was amplified with primers ITS1/ITS4 and sequenced (1). BLASTn analysis of the sequence (GenBank Accession No. JQ039331) showed a 99% homology with several isolates of F. oxysporum in the GenBank database. Pathogenicity tests were conducted on healthy, 2-month-old seedlings and 1-month-old rooted cuttings of Z. jujuba under greenhouse conditions. Plants were inoculated with sterilized mixtures of wheat and barley seeds (1:1) that were incubated in a F. oxysporum isolate spore suspension (1 × 107 conidia/ml) at 25°C for 7 to 10 days. The seeds (3 g per plant) were placed around the collar of each healthy plant under the soil surface and incubated at 25 to 28°C in a greenhouse. Control plants were sown in sterile soil without inoculated seeds. In 3 weeks, inoculated plants developed leaf wilt and chlorosis, stunted growth, brown discolored vascular tissue on stems, and finally died, which is similar to that observed in the field. F. oxysporum was reisolated from the stems of diseased plants, confirming Koch's postulates. Control seedlings were symptom free. F. oxysporum has been known to cause wilt disease on cotton and tomato in Xinjiang Province (3). However, to our knowledge, this is the first report of a natural occurrence of Chinese jujube wilt disease on commercial fields caused by F. oxysporum in China.
References: (1) G. M. Arruda et al. Plant Pathol. 54:53, 2005. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (3) F. X. Tian et al. Acta Phytopathol. Sin. 11:27, 1981.