In this article we will discuss about Fusarium. After reading this article you will learn about: 1. Habit and Habitat of Fusarium 2. Vegetative Structure of Fusarium 3. Reproduction 4. Economic Importance.

Contents:

  1. Habit and Habitat of Fusarium
  2. Vegetative Structure of Fusarium
  3. Reproduction of Fusarium
  4. Economic Importance of Fusarium

1. Habit and Habitat of Fusarium:

Fusarium is represented by large number of species which occur both in temperate and tropical regions of the world. Majority of the species are saprophytic, some are mild facultative parasite while some species are parasitic and cause serious diseases like wilt (Fig. 1) or ‘rot’ of economically important plants.

Wilt of Cajanus Cajan


2. Vegetative Structure of Fusarium:

Mycelium is branched, sepate, hyaline or coloured, inter-or intracellular and uninucleate to multinucleate. Hyphae invade the tracheids and vessels of xylem, ramify there, produce toxic substances and block them completely. As a result the plants wilt and die.


3. Reproduction of Fusarium:

It takes place by the formation of there kinds of asexual spores.These are:

(a) Micro conidia,

(b) Macro conidia, and

(c) Chlamydospores.

(a) Micro Conidia:

The micro conidia and macro conidia are produced in same sporodochia. These sporodochia develop on the surface of stem, leaves and other parts of the host plant. The fungal mycelium collects near the surface of the host tissue as anpseudoparenchymatous mass. It gets exposed by the rupturing of the epidermis (Fig. 2).

Sporodochium

From the fungal hyphae arise many short and cylindrical structures. These are conidiophores. The ultimate branches of conidophores which produce conidia are called phialides. The phialides are subulate i.e. owl shaped and have some kind of heel (characteristic of Fusarium, Fig. 3).

Phialide, Microconidia and Macroconidia

Micro conidia are small, unicellular or bi-celled, spherial or oval in shape. Their size varies from 5×15 µ x2−4 µ. They are borne single or in chains on the conidiophores by abstraction method.

(b) Macro Conidia:

The macro conidia are long, sickle or crescent shaped, multi-septate (3-5 septa), pointed at the end and broad in the middle.

They measure 15-50 µ in length and 3-5 µ in breadth. Both macro conidia and micro conidia are produced in vast numbers. They are easily disseminated by wind and after falling on the suitable substratum, they germinate and infect the host plants.

(c) Chlamydospores:

Under relatively starvation and dry conditions, the mycelial hyphae produce ovoid or spherical thick walled cells. These are called chlamydospores. They occur either single or in chains and may be terminal or intercalary (Fig. 4) in position. After maturity they get separated from the parent hyphae and act as resting spores, under favourable conditions they germinate by means of germ tubes to form a fresh mycelium.

Chlamydospores

The pseudoparenchymatous mycelium of Fusarium often forms black, compact bodies known as sclerotia. They act as storage organ and also serve as means of perennation and vegetative reproduction.


4. Economic Importance of Fusarium:

Fusarium oxysporum causes the most important vascular wilt diseases. It has several specialised forms known as form specialis (f. sp.) that infect a variety of host plant (Table 1).

Some species of Fusarium produce mycotoxins − Fumonisins and trichothecenes. It is said that these toxins may cause oesophageal cancer. Some of these toxins are said to have been used as biological war fare agents in Vietnam and Afghanistan.

Few Fusarium species like F. solani, F. Verticilloides, F. proliferatum, F. solani infect human nails (dry rot of nails) and eye. Fusarium contaminated wheat flour when eaten, immune system is weakened (neutropenia).

F. grwninearum has been used in U.K. to produce a high quality mycoprotein that can be fabricated into a number of meatless food. F. venenatum is produced industrially for use as human food quom in Europe and north America.


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