Loose smut of fungi : causual organism, symptom, disease cycle and management

 Loose smut of fungi : causual organism, symptom, disease cycle and management

A fungal disease known as loose smut causes smut spores, also known as teliospores, to replace whole heads . Symptoms of loose stools are noticeable from the outset. Smuttered heads, in which spores have taken the place of every structural element save the rachis.

Smutted heads appear many days before contrasting green, healthy heads. Smutted heads have masses of black teliospores wrapped in a gray membrane in place of grain and glume structures. Soon after heading, the spores' thin membrane breaks off, allowing the spores to either become airborne or be washed away by rain, until finally the disease's sole remnant is the empty rachis .

Total yield is lost in the diseased heads. Ill-grown heads yield no grain at all. 

Smut fungi are Basidiomycetes and include several important genera including Ustilago, Tilletia, Entyloma, and Urocystis. The most economically important smut diseases are on cereals and grasses. Examples of smut diseases are corn smut (Ustilago maydis), loose smut (Ustilago nuda), covered smut of barley (Ustilago hordei), stinking smut (Tilletia foetida), dwarf bunt of wheat (Tilletia caries), white smut (Entyloma compositarum), and onion smut (Urocystis cepulae)C

Spore masses can replace individual florets, just like loose smut can, or the entire grain head can transform into black, smutted masses enclosed within thin membranes, similar to covered smut.

Causative Agent :

A fungus named Ustilago tritici is the causal agent of loose smut of wheat. The pathogen can be detected microscopically on infected seed by embryo staining. Loose smut affects wheat, rye and triticale. 

Source and circumstances of the inoculum

A disease spread by seeds is loose smut. The contaminated seed has the fungus systemically.

Following sowing, the contaminated seed germinates and the fungus spreads throughout the seedling, invading the meristemic tissue. When the mycelia mature, they produce smutted heads when the spikes begin to form.

During flowering, wind carries teliospores from the smuttered heads to healthy plants. Spores that land on florets will germinate in humid, moderate weather. The spore's germ tube enters the ovary and grows into an embryo's mycelium. Until the asymptomatic seed germinates, the mycelium in it stays latent. 

Life cycle :

The fungus known as loose smut spreads only by seeds. Within the seed embryos is where the loose smut fungus enters the field. The fungus reactivates when the contaminated seeds sprout. It ascends within the growing points of the plant to the area where the heads are developing.

When teliospores are blown to open flowers and enter the ovary by the stigma or the ovary wall directly, the disease cycle of loose smut starts. Because Ustilago spp. have several mating types, infection can only happen when two compatible mating types coexist in a single flower.

The teliospores produce basidiospores once they arrive in an open floret. The basidiospores germinate where they are, not moving on to find another host plant. After then, a dikarytic stage is created when the hyphae of two compatible basidiospores fuse together.

The fungal mycelia attack the developing embryo in the seed after germination within the ovary. Until the following growing season, when it is sown alongside the seed, the fungus remains viable within the seed. The fungus expands along with the growing plant. When the time comes for the flowers to open, the grain is replaced by teliospores, which grow in the place of the flowers.

Indeed, compared to their healthy counterparts, plants infected with Ustilago spp. grow higher and blossom earlier. Because of this, the flowers of uninfected plants are more morphologically and physically vulnerable to infection, which benefits the infected plants. The healthy plants' open blooms receive the teliospores from the mutated grain heads, and the

In charge

By planting premium pathogen-free seed, the source of the inoculum will be removed.

All wheat seed should be treated with systemic fungicide (carboxin, triaminemol) to assist lower disease levels.

Using resistant cultivars aids in lowering symptoms at the end.

By keeping seed production fields far from commercial crops, airborne spores that can travel great distances on windborne breezes are prevented from infecting the seed.  

Symptoms of damage

Up until the head emerges, Ustilago nuda f.sp. tritici infection is undetectable. An ear that has become smuttered is the first indication of infection. The ear is filled with a mass of olive-brown smut spores instead of normal tissue.

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