Physiology and molecular aspects of Verticillium wilt diseases caused by V. dahliae and V. albo‐atrum

Abstract

Kingdom: Fungi, phylum: Ascomycota, subphylum, Pezizomycotina, class: Sordariomycetes, order: Phyllachorales, genus: Verticillium. Host range and disease symptoms: Over 200 mainly dicotyledonous species including herbaceous annuals, perennials and woody species are host to Verticillium diseases. As Verticillium symptoms can vary between hosts, there are no unique symptoms that belong to all plants infected by this fungus. Disease symptoms may comprise wilting, chlorosis, stunting, necrosis and vein clearing. Brown vascular discoloration may be observed in stem tissue cross-sections. Pathogenicity: Verticillium spp. have been reported to produce cell-wall-degrading enzymes and phytotoxins that all have been implicated in symptom development. Nevertheless, evidence for a crucial role of toxins in pathogenicity is inconsistent and therefore not generally accepted. Microsclerotia and melanized mycelium play an important role in the disease cycle as they are a major inoculum source and are the primary long-term survival structures. Resistance: Different defence responses in the prevascular and the vascular stage of Verticillium wilt diseases determine resistance. Although resistance physiology is well established, the molecular processes underlying this physiology remain largely unknown. Resistance against Verticillium largely depends on the isolation of the fungus in contained parts of the xylem tissues followed by subsequent elimination of the fungus. Although genetic resistance has been described in several plant species, only one resistance locus against Verticillium has been cloned to date. Useful website: http://cbr-rbc.nrc-cnrc.gc.ca/services/cogeme/

Proteomics-based analysis reveals that Verticillium dahliae toxin induces cell death by modifying the synthesis of host proteins

“…After penetrating the cortex of the root, the fungus passes through the endodermis, invades the xylem vessels, eventually reaching the aerial parts of the plant (Tzima et al 2011). Typical disease symptoms may comprise wilting, stunting, leaf necrosis, vascular plugging and brown vascular discoloration (Fradin and Thomma 2006). There are currently no fungicides available to control Verticillium wilt once plants have been infected (Klosterman et al 2009).…”

“…Historically, there are two seemingly contradictory hypotheses concerning the mechanism of Verticillium wilt. One hypothesis states that Verticillium wilt results from toxin activity, whereas the other states that it is predominantly the result of vessel occlusion in the plant (Fradin and Thomma 2006). Some studies suggest that crude V. dahliae extracts containing some phytotoxic factors, such as protein-lipopolysaccharide complex (PLPC), glycoproteins, small peptides and/or cell-wall-degrading enzymes, can damage leaf and root cell membranes, resulting in ion leakage (Gour and Dube 1985).…”

“…The microsclerotial form of V. dahliae can remain viable in the soil for more than 20 years (Wilhelm 1955). In 1967, the pathogen was identified as the causal agent of this important disease of cotton under field conditions, and it has been a major threat to cotton production since then (Fradin and Thomma 2006).…”

Verticillin A is likely not produced by Verticillium sp.

“…As many Verticillium sp. are known phytopathogens, 3 and Cochliobolus carbonum has been shown to produce the histone deacetylase inhibitor HC-toxin as a virulence factor, 4 it is possible that Verticillin A might constitute another fungal means to interfere with the host's chromatin remodeling machinery for enhancing pathogenesis. In fact, two other ETPs, Gliotoxin (from Aspergillus fumigatus) and Sirodesmin (from Leptosphaeria maculans), have been identified as virulence factors.…”

Comparative Efficacy of Potassium Salts Against Soil-borne and Air-borne Fungi and Their Ability to Suppress Tomato Wilt and Fruit Rots

“…Management of these pathogens is difficult due not only to their endogenous growth, but also to the multi-years longevity of their resting structures in the soil (chlamydospores and microsclerotia) and to the inefficacy of fungicides once they reach the xylem [4][5][6][7]. Moreover, in Tunisia, tomato is regarded as one of the most important crops in terms of both value and cropped areas [8] and its continuous cropping leads to a buildup of fungal resting structures in the soil, resulting in substantial disease problems as well as the emergence of new races of these pathogens that overcome plant resistance [9][10][11].…”