Pathogenicity, Virulence, and Vegetative Compatibility Grouping of Verticillium Isolates from Spinach Seed

Abstract

Iglesias-Garcia, A. M., Villarroel-Zeballos, M. I., Feng, C, du Toit, L. J., and Correll, J. C. 2013. Pathogenicity, virulence, and vegetative compatibility grouping of Verticillium isolates from spinach seed. Plant Dis. 97:1457-1469.In 2005, Verticillium dahliae was first reported to be pathogenic to spinach seed crops in the Pacific Northwest, with symptoms only developing after initiation of the reproductive stage of plant growth, and to be prevalent on commercial spinach seed lots produced in Denmark, The Netherlands, and the United States. In this study, the genetic diversity, pathogenicity, and virulence were examined for a collection of isolates of Verticillium spp. from spinach as well as other hosts (alfalfa, cotton, lettuce, mint, peppermint, potato, radish, and tomato) from various countries and from different vegetative compatibility groups (VCGs). Of a total of 210 isolates of V. dahliae obtained from spinach seed produced in Denmark, the Netherlands, New Zealand, or the United States, 128 were assigned to VCG 4B (89% of 91 U.S. isolates, 86% of 42 isolates from the Netherlands, 19% of 43 Denmark isolates, and 8% of 13 New Zealand isolates), 65 to VCG 2B (92% of the New Zealand isolates, 79% ofthe Denmark isolates, 14% ofthe Netherlands isolates, and 9% of the U.S. isolates), and 3 to VCG 2A (2% of each of the Denmark and U.S. isolates, and 0% of the Netherlands and New Zealand isolates); 14 isolates could not be assigned to a VCG. Although little variation in the sequence of the internal transcribed spacer (ITS) region of ribosomal DNA was observed among isolates within each Verticillium sp., the ITS region readily differentiated isolates of the species V. dahliae, V. tricorpus, and Gibellulopsis nigrescens (formerly V. nigrescens) obtained from spinach seed. Greenhouse pathogenicity assays on spinach, cotton, lettuce, and tomato plants using isolates of V. dahliae (n = 29 to 34 isolates), V. tricorpus {n = 3), G. nigrescens (n = 2), and V albo-atrum (n = 1) originally obtained from these hosts as well as from alfalfa, mint, peppermint, potato, and radish, revealed a wide range in virulence among the isolates. Isolates of V. tricorpus and G. nigrescens recovered from spinach seed and an isolate of V. albo-atrum from alfalfa were not pathogenic on spinach. In addition, isolates of V. dahliae from mint and peppermint were not pathogenic or only weakly virulent on the hosts evaluated. Although there was a wide range in virulence among the isolates of V. dahliae tested, all of the V. dahliae isolates caused Verticillium wilt symptoms on spinach, lettuce, tomato, and cotton. None of the isolates of V. dahliae showed host specificity. These results indicate that Verticillium and related species associated with spinach seed display substantial variability in virulence and pathogenicity to spinach and other plants but the V. dahliae isolates were restricted to three VCGs.

The endophyteVerticillium Vt305 protects cauliflower against Verticillium wilt

“…Endophytism seems to be a common phenomenon in the genus Verticillium, although often overlooked (Lacy and Horner 1966;Malcolm et al 2013). It has been demonstrated that certain isolates of V. dahliae, V. alboatrum and V. tricorpus can colonize their hosts and yet cause no or minor vascular discolouration and do not develop external symptoms (Skotland 1971;Ebihara et al 2003;Chen et al 2004;Robinson et al 2006;Qin et al 2008;Iglesias-Garcia et al 2013;Malcolm et al 2013). However, it is still unclear whether the endophytic behaviour is generally an intrinsic characteristic of certain isolates or rather the outcome of specific interactions between potential pathogenic isolates and some hosts (Malcolm et al 2013).…”

High‐Throughput Assessment and Genetic Investigation of Vegetative Compatibility in Verticillium dahliae

“…In addition, significant differences in morphology and physiology have been reported between different VCGs (Korolev et al 2000;Zeise and von Tiedemann 2001;Papaioannou et al 2013b). The phytopathological significance of VCG analyses for V. dahliae populations is reflected in the unabated frequency of relevant reports in the literature (some recent examples include Dung et al 2013;El-Bebany et al 2013;Iglesias-Garcia et al 2013;Papaioannou et al 2013b).…”

Multiplex real-time PCR assays for detection of four seedborne spinach pathogens

“…cicla ), Peronospora variabilis (cause of downy mildew on quinoa, Chenopodium quinoa ), Verticillium tricorpus and Verticillium nigrescens (saprophytes or weak pathogens of spinach often found associated with spinach seed) (Iglesias‐Garcia et al . ), V. albo‐atrum (from alfalfa, Medicago sativa ), V. fungicola (from mushroom), Colletotrichum dematium (cause of spinach anthracnose), Fusarium oxysporum f. sp. spinaciae (cause of Fusarium wilt of spinach), and multiple saprophytic fungal isolates including F. oxysporum , Alternaria spp., Phoma spp., Epicoccum spp.…”

“…; Iglesias‐Garcia et al . ). Additionally, Cladosporium leaf spot, caused by Cladosporium variabile , and Stemphylium leaf spot, caused by Stemphylium botryosum , have recently emerged as problems for spinach production as well as spinach seed production (Fuentes‐Davila and Gabrielson ; Everts and Armentrout ; Koike et al .…”

“…However, V. dahliae can be highly problematic for spinach seed production (du Toit et al 2005c), and seed transmission of V. dahliae may introduce the pathogen into new production areas (Atallah et al 2010). The latter is potentially problematic because some strains of V. dahliae have a broad host range, and spinach is often rotated with high-value vegetables and fruits, including lettuce and strawberry, which can be devastated by V. dahliae (Atallah et al 2010;Iglesias-Garcia et al 2013). Additionally, Cladosporium leaf spot, caused by Cladosporium variabile, and Stemphylium leaf spot, caused by Stemphylium botryosum, have recently emerged as problems for spinach production as well as spinach seed production (Fuentes-Davila and Gabrielson 1996;Everts and Armentrout 2001;Koike et al 2001Koike et al , 2005Derie 2001, 2012;Reed et al 2010).…”