EPWS 310 - PLANT PATHOLOGY

LECTURE 14: ASCOMYCETES Vascular wilts

Fusarium, Verticillium and Ceratocystis

Pages 522-534

VASCULAR WILTS

These are extremely serious diseases from the catastrophic Dutch elm disease to the garden variety Fusarium and Verticillium wilts.

Vascular wilts have many characteristics in common and can often be confused, there are only five species responsible for all of this damage.

Fusarium oxysporum - very wide host range

Verticillium dahliae - very wide host range

Verticillium albo-atrum - very wide host range

Ophiostoma ulmi - Elm tree wilt

Ceratocystis fagacearum - Oak wilt

All wilt diseases caused by Fusarium and Verticillium have very similar symptoms. Initially a wilt of the herbaceous plant parts often recovering overnight in the very early stages but quickly becoming a permanent wilt leading to necrosis of the herbaceous parts and plant death.

The pathogens enter into the xylem vessels and may move up the xylem by hyphal extension or by microconidia. Toxins are involved in many diseases leading to symptoms in advance of the pathogen and foliar symptoms such a vein chlorosis and general cholorosis. Tyloses form and excessive xylem parenchyma proliferation occurs all to block the water flow.

Leaf epinasty and defoliation may also occur.

Diseases are made far worse in the presence of root invading nematodes such as Meloidogyne.

Fusarium is a soil inhabitant and Verticillium is a soil invader. They have very similar life cycles and neither have a sexual stage (Teleomorph).

However both are able to survive in soil for very long periods because they have specialized structures for survival.

Fusarium oxysporum has chlamydospores:

Verticillium dahliae has microsclerotia:

Verticillium albo-atrum has thickened hyphae:

These are very common structures in many soil fungi for survival.

LIFE CYCLE of F.o. lycopersici FIG 11-105

Fusarium oxysporum occurs in about 300 formae specialis affecting hundreds of plants. These may be further divided into races. All defined entirely by host genetics.

Worldwide fungus - everywhere and most common as a saprophyte.

Verticillium these fungi are also widespread but do not fall into pathological forms or races very neatly. They tend to cause wilt at lower temperatures than Fusarium but there are exceptions!

Verticillium is also more likely to cause defoliation than Fusarium.

V. dahliae prefers higher temperature than V. albo-atrum and is common in warmer areas. Serious here on cotton and chile.

Control ??

Ophiostoma ulmi  follows a similar pattern.

LIFE CYCLE FIGURE 11-109

Associated with bark beetles, spreads through natural root grafts.

Control??

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