First Report of Lavender Wilt Caused by Fusarium solani in China

Lavender (Lavandula angustifolia Mill) is grown commercially in Xinjiang Province of China for its medicinal properties and as a perfume plant. In the spring of 2004 and 2005, a wilt disease was observed in irregular patches in several fields resulting in as much as 15%-30% yield loss. Diseased plants exhibited symptoms of chlorosis, stunting, wilting, and death and did not reestablish vegetative growth. Longitudinal sections through stems and roots showed severe necrosis in vascular tissues. Pathogen isolations were made from stems and roots on potato dextrose agar (PDA). Colonies were woolly to cottony with cream to white aerial mycelium and a cream reverse on PDA media. Observed sporodochia were usually moist and blue-green colored. Macroconidia were moderately curved, stout, thick-walled, usually 3-5 septate, 3.5-5.7 x 27-50µm long, and are borne on short conidiophores that soon formed sporodochia. Microconidia, formed on long monophialides, were one to three-celled, 2.4-5 x 9.1-15.8 µm long, and occurred in false heads. Chlamydoconidia occurred both singly and in pairs. The pathogen was identified as Fusarium solani based upon colony and conidial morphology (Wang et al. 1996). The identification was confirmed by comparison of ITS (internal transcribed spacer) sequences. The ITS region of rDNA was amplified by polymerase chain reaction (PCR) with primers ITS1/ITS4 and sequenced (Arruda et al. 2005). BLAST analysis of the sequence obtained showed a 100% homology with several isolates of F. solani in the GenBank database.

Pathogenicity tests were conducted on 4-month-old seedlings and on 2-month-old rooted cuttings under greenhouse conditions. For plant inoculations, sterilized mixtures of wheat and barley seeds (1:1) were incubated in a F. solani spore suspension (1 x 10⁷ conidia/ml) at 25°C for 7-10 days. Noninoculated seeds served as negative controls. Seeds were placed around the collar of each plant under the soil surface (3g of seeds/plant). Plants were irrigated and placed in a greenhouse with temperatures ranging from 25 to 28°C. All inoculated plants developed wilt symptoms similar to that observed in the field within 2 weeks after inoculation. The pathogen was reisolated from the vascular tissues of inoculated plants on PDA as previously described and the morphological characteristics were identical to the original isolates. Fusarium solani is known to cause disease on sugar beet, cotton and tomato in Xinjiang Province (Ding et al. 2000; Li et al., 2001). However, to our knowledge, this is the first report of a natural occurrence of Fusarium wilt caused by Fusarium solani on commercial field lavender in China.