Differentiation ofVerticillium dahliae populations on the basis of vegetative compatibility and pathogenicity on cotton

Abstract

Complementary auxotrophic nitrate-nonutilizing (nit) mutants were used to investigate vegetative compatibility within 27 strains of Verticillium dahliae isolated from several hosts originating from Africa, Asia, Europe and the United States. Using about 500 nit mutants generated from these strains, three vegetative compatibility groups, 1, 2 and 4, were identified. Simultaneously, virulence of each strain was assessed on cultivars of Gossypium hirsutum, G. barbadense and G. arboreum, based upon Foliar Alteration Index (FAI) and Browning Index (BI) estimation. The strains in VCG1 were of both the cottondefoliating pathotype and race 3 (on cotton) but were non pathogenic on tomato; those in VCG2 and VCG4 were of the nondefoliating pathotype and belonged to different races on cotton and on tomato. Hyaline mutants deriving from parental wild-type strain showed differences in pathogenicity but were always assigned to the parental VCG. A relationship was established between VCGs and the taxonomic position of host plants. Data from nit pairings indicated that the sub-populations of V. dahliae (VCGs) may not be completely isolated genetically.

Verticillium wilt of olive: a case study to implement an integrated strategy to control a soil-borne pathogen

“…On the other hand, considering VCGs as fully genetically isolated groups may be a strict statement. In fact, the existence of weak complementation and formation of heterokaryons between isolates belonging to different VCGs (or certain subgroups), or even between different Verticillium species, has been described (Daayf et al 1995;Hiemstra and Rataj-Guranowska 2003;Joaquim and Rowe 1990;Strausbaugh et al 1992). This may suggest the existence of a continuum of genetic variation surpassing the genetic barrier of the VCG.…”

“…The study of VCGs has traditionally served to explore genetic diversity in V. dahliae populations from the perspectives of geographical origin and/or plant host provenance of isolates. Currently, VCG1 (A and B), VCG2 (A and B), and VCG4 (A and B) (Chen 1994;Daayf et al 1995;Dobinson et al 2000;Rowe 1990, 1991;andKorolev et al 2000, 2001;Strausbaugh et al 1992;Zhengjun et al 1998) are fully accepted. The differentiation into subgroups A and B is based on the frequency and vigor of nit mutant complementation (Joaquim and Rowe 1991;Strausbaugh 1993).…”

“…Thus, some studies support the correlation between VCG assignment of isolates and their differential virulence displayed in a given plant (Joaquim and Rowe 1990;Bhat and Subbarao 1999;Tsror et al 2001;Korolev et al 2001), whereas others conclude that different isolates from the same VCG show different degrees of virulence in a same crop (Elena 1999;Korolev et al 2000Korolev et al , 2001. Interesting examples pointing to an association between genetic groups and host specificity are: i) the predominance of isolates assigned to VCG4 in potato (Solanum tuberosum L.) infections in the United States and Israel (Joaquim and Rowe 1991;Strausbaugh et al 1992;Korolev et al 2000); ii) the aforementioned association of the highly-virulent, D-pathotype isolates of cotton (Gossypium hirsutum L.) with their assignment to VCG1A described in various areas such as Central Asia, China, Israel, Peru, Spain, Turkey and USA (Daayf et al 1995;Korolev et al 2001;Zhengjun et al 1998;Korolev et al 2008;Dervis et al 2008), in what may constitute an example of dispersal of isolates from an original focus of infected cotton genotypes; or iii) the prevalence of VCG2A and 2B isolates infecting artichoke (Cynara scolymus L.) in a defined artichokecultivating region of eastern-central Spain, with VCG2B being the most virulent in this host . Studies regarding to olive-infecting V. dahliae isolates, are indicating the following scenario: 1) highly-virulent isolates, inducing severe syndromes in olive, generally belong to the D pathotype; 2) all olive D-pathotype isolates have so far been assigned to VCG1A in all countries where this group/pathotype has been reported (Pérez-Artés et al 2000;Collado-Romero et al 2006;Dervis et al 2010); and 3) olive isolates assigned to other VCGs (namely, VCG2 and VCG4) have been characterized as ND pathotype either by pathogenicity testing or by PCR-based molecular pathotyping (Fig.…”

The use of vegetative compatibility tests for identification of biodiversity of phytopathogenic fungi

“…Several studies have shown that strains of similar pathogenicity belong to the same VCG (Strausbaugh et al, 1992;Daayf et al, 1995;Dervis et al, 2009). Strains belonging to Fusarium oxysporum f. sp.…”

First report of the presence of Verticillium dahliae VCG1A in Australia

“…The cotton defoliating strain T9 (the original defoliating pathotype from cotton in California) belongs to subgroup VCG1A (Bell 1994). Only isolates of this subgroup caused severe defoliation of cotton in previous studies (Daayf et al 1995;Korolev et al 2008). Thus, isolates strongly compatible with T9 (or strongly compatible with other testers) may be assigned to VCG1A (Korolev et al 2008).…”