Fusarium wilt is a common vascular wilt fungal disease exhibiting symptoms of wilting or dying of plants, it is among the most serious diseases of plants that can put a grower / farmer out of business.
The pathogen that causes Fusarium wilt is Fusarium oxysporum and the species is divided into forma specilis depending on the host crop
Disease Cycle and Development
Fusarium oxysporum is the most widely dispersed of the Fusarium species and is found worldwide. F. oxysporum has no known sexual stage, but produces three types of asexual spores: microconidia, macroconidia, and chlamydospores. The microconidia are the most abundantly produced spores. They are oval, elliptical or kidney shaped and produced on aerial mycelia. Macroconidia, which have three to five cells and have gradually pointed or curved edges, are found on sporodochia on the surface of diseased plant (in culture the sporodochia may be sparse or nonexistent). Chlamydospores are usually formed singly or in pairs, but can sometimes be found in clusters or in short chains. They are round thick walled spores produced within or terminally on an older mycelium or in macroconidia. Chlamydospores unlike the other spores can survive in the soil for a long period of time.
Fusarium oxysporum is a common soil pathogen and saprophyte that feeds on dead and decaying organic matter. It survives in the soil debris as a mycelium and all spore types, but is most commonly recovered from the soil as chlamydospores. This pathogen spreads in two basic ways: it spreads short distances by water splash, and by planting equipment, and long distances by infected transplants and seeds. F. oxysporum infects a healthy plant by means of mycelia or by germinating spores penetrating the plant root tips, root wounds, or lateral roots. The mycelium advances intracellularly through the root cortex and into the xylem. Once in the xylem, the mycelium remains exclusively in the xylem vessels and produce microconidia (asexual spores. The microconidia are able to enter into the sap stream and are transported upward.
Where the flow of the sap stops the microconidia germinate. Eventually the spores and the mycelia clog the vascular vessels, which prevent the plant from up-taking and translocating nutrients. In the end the plant transpires more than it can transport, the stomata close, the leaves wilt, and the plant dies. After the plant dies the fungus invades all tissues, sporulates, and continues to infect neighboring plants.
Environment Where It Thrives Best
Previously stated F. oxysporum is a common soil saprophyte that infects a wide host range of plant species around the world. It has the ability to survive in most soil—arctic, tropical, desert, cultivated and non-cultivated. Though Fusarium oxysporum may be found in many places and environments, development of the disease is favored by high temperatures and warm moist soils. The optimum temperature for growth on artificial media is between 25-30 °C, and the optimum soil temperature for root infection is 30 °C .However, infection through the seed can occur at temperatures as low as 14 °C.
Host Crops and Symptoms
- Hosts: Tomato, tobacco, legumes, cucurbits, sweet potatoes and banana
- The fungal pathogen Fusarium oxysporum affects a wide variety of hosts of any age. Tomato, tobacco, legumes, cucurbits, sweet potatoes and banana are a few of the most susceptible plants, but it will also infect other herbaceous plants .Fusarium oxysporum generally produces symptoms such as wilting, chlorosis, necrosis, premature leaf drop, browning of the vascular system, stunting, and damping-off. The most important of these is vascular wilt. Fusarium wilt starts out looking like vein clearing on the younger leaves and drooping of the older lower leaves, followed by stunting of the plant, yellowing of the lower leaves, defoliation, marginal necrosis and death of the plant. On older plants, symptoms are more distinct between the blossoming and fruit maturation stages.
- Fusarium oxysporum is split into divisions called formae speciales (singular forma specialis, abbreviated f.sp.). There are over 100 formae speciales divisions, each with one or two different races. Each forma specialis within the species are host-specific (i.e. specific to a certain plant) and produce different symptoms:
- oxysporum f. sp. batatas affects sweet potato. The symptoms include leaf chlorosis, stunting, and leaf drop. It is transmitted through the soil and through vascular wounds in plant material.
- oxysporum f.sp. betae affects sugar beets while F. oxysporum f.sp. Phaseoli affects Dry beans, severely affected plants yellow, wilt, and die prematurely which causes yield reduction or total crop losses
- oxysporum f. sp. cubense causes Panama disease on banana. It is found everywhere bananas are grown in Africa, Asia, Central and South America. It attacks banana plants of all ages and spreads mainly through the soil. It causes wilting and yellowing of the leaves.
- oxysporum f. sp. lycopersici causes vascular wilt in tomato. The disease starts out as yellowing and drooping on one side of the plant. Leaf wilting, plant stunting, browning of the vascular system, leaf death, and lack of fruit production also occur.
- oxysporum f. sp. Melonis attacks melons, muskmelon and cantaloupe. It causes damping-off in seedlings and causes chlorosis, stunting and wilting in old plants. Necrotic streaks can appear on the stem.
- TREATMENT AND CONTROL MEASURES
- PYRAMID 50G/20L FOLIAR SPRAY AND 100GM /20LTR AS DRENCH
- CHARIOT 20MLS/20L DRENCH
- CHARIOT 20MLS/20MLS AS SPRAY
- RANSOM 15G/20MLS AS SPRAY AND DRENCH
Drenches of fungicides should start early after germination and repeated every 3 weeks to 1 month.
