''Verticillium nonalfalfae'' is a soilborne

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

in the order

Hypocreales The Hypocreales are an order of fungi within the class Sordariomycetes. In 2008, it was estimated that it contained some 237 genera, and 2647 species in seven families. Since then, a considerable number of further taxa have been identified, in ...

. It causes

verticillium wilt Verticillium wilt is a wilt disease affecting over 350 species of eudicot plants. It is caused by six species of ''Verticillium'' fungi: ''V. dahliae'', ''V. albo-atrum'', ''V. longisporum'', ''V. nubilum'', ''V. theobromae'' and ''V. tricorpu ...

in some plant species, particularly '' Ailanthus altissima''. The fungus produces a resting

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...

characterized by brown-pigmented

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e. It is most closely related to '' V. dahliae'' and '' V. alfalfae''. Verticillium wilt on hops

Foliar symptoms on hops caused by Verticillium

Description

It is not possible to differentiate ''V. nonalfalfae'' and ''V. alfalfae'' from ''V. albo-atrum'' consistently using only morphological features. ''Verticillium albo-atrum'' may be found in co-infections with ''V. nonalfalfae'' on some hosts. The hyphae penetrate the root epidermal cells of hosts and enter the xylem.

Host and symptoms

''Verticillium nonalfalfae'' has a wide host range including hops, kiwifruit, spinach, solanaceous plants like eggplants and potatoes, and tree of heaven (''A. altissima).'' Systemic infections appear on most hosts showing vascular wilts caused by xylem blockage. Additional symptoms including vascular discoloration and defoliation show almost exclusively on ''A. altissima.'' ''V. nonalfalfae'' tends not to infect non-target plants. In contrast with ''V. alfafae'', it does not infect

alfalfa Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, and silage, as w ...

Impact on hops

One important host of ''V. nonalfalfae'' is

hops Hops are the flowers (also called seed cones or strobiles) of the hop plant ''Humulus lupulus'', a member of the Cannabaceae family of flowering plants. They are used primarily as a bittering, flavouring, and stability agent in beer, to whi ...

, with infections found both in the United States and most places around the world. The symptoms of hosts infected by ''V. nonalfalfae'' on hops are categorized into two pathotypes: mild and lethal. Mild pathotypes primarily cause symptoms of curling and leaf tissue death. Hops infected by ''V. nonalfalfae'' with the mild pathotype generally can survive the infection. For the lethal pathotype of ''V. nonalfalfae'' on hops, hosts suffer from rapid weakening that ultimately leads to death. The lethal form was discovered in hops in the 1940s in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

and elsewhere in Europe later. Two pathotypes share similar peroxidase, which are thought to be contribute to their pathogenicity.

Disease cycle

The disease cycle of ''Verticillium nonalfalfae'' is similar to that of other members of the genus. ''V. nonalfalfae'' overwinters by forming a resting mycelium in the soil. However, unlike ''V. dahliae'', for example, it does not produce

microsclerotia A sclerotium (; (), is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favor ...

. ''Verticillium nonalfalfae'' infects in the spring via

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

in the soil; conidia are borne on conidiophores. It has been found that intraspecific grafting enhances ''V. nonalfalfae''’s dispersal of conidia, that is, conidia from diseased roots can be transported to healthy root tissues. Conidia can be transmitted through mechanical dispersal, whereby the conidia become attached to cutting tools. In the case of hops, the fungus can spread during soil cultivation, via plantings from infested yards, and through soil moved by equipment and workers. Long-distance transportation of conidia involves insects such as

ambrosia beetle Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae ( Coleoptera, Curculionidae), which live in nutritional symbiosis with ambrosia fungi. The beetles excavate tunnels in dead, stressed, and healthy trees in wh ...

s, which are thought to be critical in creating regional outbreaks of wilting in ''Ailanthus''.

Biological control of tree of heaven

Another important host of ''V. nonalfalfae'' is ''Ailanthus altissima,'' also known as tree of heaven. This species of ''Ailanthus'' was introduced in the northeastern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

from the 1790s, and is now a forest management problem in 40 of the 48 contiguous states. Spreading widely and quickly, it is considered to be an

Invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

. ''V. nonalfalfae'' is being studied as a biological control of ''A. altissima''. Symptoms of verticillium wilt on tree of heaven appear quickly after inoculation, according to studies. A vector of the wilt is the weevil ''

Eucryptorrhynchus brandti ''Eucryptorrhynchus brandti'', the snout weevil, is an insect in the weevil family. In its native range in China, it causes significant damage to its single host, '' Ailanthus altissima'', tree of heaven. Thus the weevil is under study as a b ...

''.

References

External links

*
MycoBank
{{Taxonbar, from=Q20721590 Fungal plant pathogens and diseases Fungi described in 2011 Hypocreales incertae sedis