First Report of Verticillium Wilt Caused by V. dahliae on Grafted Solanum aethiopicum in Washington

Abstract

Solanum aethiopicum L., previously S. integrifolium Poir. (4), has been used as a rootstock for commercial, grafted eggplant production throughout Asia (3). In August 2010 and 2011, symptoms of Verticillium wilt were observed on ‘Epic’ eggplant (S. melongena L.) grafted onto S. aethiopicum at two sites with a history of the disease: one in the irrigated, dryland Columbia Basin of eastern Washington near Eltopia, and the other in maritime western Washington near Mount Vernon. Interveinal chlorosis, V-shaped necrotic lesions, and wilting were evident at both sites in both years. Each year, stems of 20 symptomatic plants from each field site were cut at the soil line to a 20-cm length, surface sterilized for 5 min in a 10% bleach solution, rinsed in tap water for 30 s, cut longitudinally, and incubated in moisture chambers for 4 weeks at room temperature in the dark. Microsclerotia that formed in the stems were typical of those produced by V. dahliae. One isolate, ‘MVEgg301’, from an infected stem at Mount Vernon, developed dark microsclerotia and verticillate conidiophores in a radiating pattern, typical of Verticillium on half-strength potato dextrose agar (1/2 PDA) medium. The internal transcribed spacer (ITS) region of rDNA amplified by PCR assay using primers ITS6 and ITS4 from mycelia sampled directly from 1/2 PDA media revealed a 100% match with ITS rDNA sequences of >50 V. dahliae accessions in GenBank (1). Pathogenicity of ‘MVEgg301’ was assessed in two tests. In both, 12 each of non-grafted and grafted (with cv. Epic) S. aethiopicum plants were inoculated with ‘MVEgg301’ by cutting approximately 5 mm off the root tips and dipping the remaining roots in a suspension of 106 conidia/ml for 5 s. Similarly, 12 each of non-grafted and grafted S. aethiopicum plants were cut and dipped similarly in sterile water as controls. Chlorosis, necrosis, and wilting were observed in 11 of the 12 inoculated, non-grafted plants and 8 of the 12 inoculated, grafted plants in Test I. The same symptoms were observed in 10 of the 12 inoculated, non-grafted plants and 10 of the 12 inoculated, grafted plants in Test II. V. dahliae was reisolated and confirmed from symptomatic, inoculated non-grafted and grafted plants using the stem assay and direct PCR assay described above. Chlorosis, necrosis, and wilting were observed in one non-grafted control plant in Test I, and two non-grafted and four grafted control plants in Test II. The symptoms were mild and likely due to nutritional deficiencies; microsclerotia were not observed in any assayed water-inoculated plant stems. Although there are several reports of V. albo-atrum infecting S. aethiopicum in the United States (2), to our knowledge, this is the first report of V. dahliae causing Verticillium wilt on this eggplant species. This finding is significant because S. aethiopicum is used as a rootstock for control of soilborne diseases like Verticillium wilt in commercial grafted eggplant production (3). References: (1) G. Calmin et al. Biotechnol. Biotechnol. Equ. 21:40, 2007. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN, 1989. (3) M. Oda. Food Fert. Technol. Ctr. Ext. Bul. 480:1, 1999. (4) PBI Solanum Project. 2012. Solanaceae Source. Accessed at http://www.nhm.ac.uk/solanaceaesource/ . Natural History Museum, London, 29 Aug. 2012.

Plant Growth, Fruit Yield and Quality, and Tolerance to Verticillium Wilt of Grafted Watermelon and Tomato in Field Production in the Pacific Northwest

“…Verticillium wilt symptoms were not observed in non-grafted, self-grafted, or grafted 'Cherokee Purple' heirloom tomato at either location in either year. However, eggplant planted immediately adjacent to the tomato study at both locations in both years developed severe and obvious symptoms of verticillium wilt (Johnson et al, 2013). Although eggplant is reported to be very susceptible to V. dahliae (O'Brien, 1983), higher soil populations may be required to cause damage on tomato.…”

Grafting for managing vegetable crop pests

“…22 Verticillium wilt caused by V. dahliae was first reported in eggplant species Solanum aethiopicum L. rootstocks in Washington, USA. 23 Eggplant grafted on Beaufort tomato rootstock had the lowest Verticillium wilt severity and greater marketable fruit weight compared to nongrafted eggplant, self-grafted, and S. aethiopicum grafted eggplant. 22 Thus, grafting susceptible eggplant scions on resistant rootstocks can be useful to reduce incidence of Verticillium wilt and increase eggplant fruit yields in Verticillium-infested soils.…”

“…Verticillium dahliae is a highly destructive disease of eggplant ( Solanum melongena L.) and all eggplant cultivars are susceptible to this soil‐borne fungal pathogen 22 . Verticillium wilt caused by V. dahliae was first reported in eggplant species Solanum aethiopicum L. rootstocks in Washington, USA 23 . Eggplant grafted on Beaufort tomato rootstock had the lowest Verticillium wilt severity and greater marketable fruit weight compared to nongrafted eggplant, self‐grafted, and S. aethiopicum grafted eggplant 22 .…”