Fungal, Viral and Algal plant diseases.

Fungal, Viral and Algal plant diseases.

Diseases caused by Fungi:

Powdery mildew, which is also known as oidium is caused by the fungus Uncinula nector and is the most common and widespread disease of grapevines. It occurs in mild to severe from North and South America, Europe, parts of Africa and Australia.

Pathogen:

The main fungal plant disease is Uncinula necator (Teleomorph of the pathogen) (syn. Erysiphe necator ). The fungus has a narrow host range that attacks only green tissue on the grapevine, with leaves and young berries. It is an obligate parasite which need a green plat tissue as a host. If it is untreated can cause crop loss and poor wine quality. In the sexual stage of the pathogen, to release ascospores from its cleistothecia in the spring, it requires free moisture. These fungi iscalled as cleistothecia as they can remain for longer periods in fruiting bodiese of plants.

Classification:

Kingdom : Fungi

Division : Ascomycota

Class : Leotimycetes

Order : Erysiphales

Family : Erysiphaceae

Genus : Uncinula

Species : necator

Host :

The main host of this fungal disease in Grapevine (Vitis spp )

Symptoms :

The symptoms of this fungal disease is described below:

• The fungus infects all green tissues of the grapes.
• The presence of white or grayish-white powdery patches in leaves.
• the heavily infected leaves may turn dull, dry out and drop.
• Young leaves are infected, distorted and stunted.
• The shoots have dark brown to black lesions.
• The fruits are white and powdery or with the dark and dusty lesion.
• It also causes defoliation of vines.
• Its buds can only be affected by the fungal pathogen as it is an open part and not surrounded by the ring of senescent tissue.

Disease Cycle :

The fungus produces small black spherical fruiting bodies which are called cleistothecia that are present on the surface of infected leaves, shoots, and berries. The first (primary) infections are not clearly visible and occur in leaves near the trunk of vine where cleistothecia are produced. After colonies/ mycelia have developed from the primary infection or flag-shoots have emerged the fungus produces the white mass of conidia which is white powdery. The pathogen survives in the diseased buds, fallen berries and through the cleistothecia. In buds, they remain dormant until the following season. When the buds break, the fungus is reactivated and shoots growing from infected buds become covered with white mycelium. Conidia are produced abundantly on these infected shoots (flag shoots) and are readily disseminated by the wind. Cleistothecia are washed by rain to the bark of vine where they overwinter.

Diseases management :

The disease can be managed by following methods:

1. The diseased parts can be trimmed.
2. The process of dusting with sulfur can be done in diseased parts.
3. The foliar parts can be sprayed with fungicides.

Diseases caused by Viruses/ Mesobiotic :

Viral Diseases :

Pathogen :

Tobacco mosaic virus (ToMV)

Group : +ss

Genus : Tobamovirus

Species : Tomato Mosaic Virus

Host :

The important hosts of viral plant disease are Tomato (Lycopersicon esculentum). It is affected by major pathogen including viruses.

Disease:

The main diseases caused by the virus in the plant is Tomato Mosaic Virus (ToMV).

Symptoms:

The main symptoms of viral plant disease is described as follow:

• The affected tomato plants show mottling in its foliage parts , with alternating yellowish and darker green areas.
• The green areas are thicker and raised giving a blister-like appearance.
• The younger leaves may be twisted and tend to be fern-like in appearance with pointed tips.
• Necrotic spots and yellow blotches and may occur on both ripe and green fruit.
• There may be internal browning of fruit and its distortion may occur.
• The flowers can be discolored and entire plant may be dwarfed.

Pathology:

The virus may be introduced on the infected seed which can spread through contaminated tool, clothes and hands of the worker during routine activities. It enters the plant through minor wounds. The infection is localized initially but spreads via vascular system and turn out to be the systemic infection. The positive (+) sense viral RNA serves as mRNA and is translated to produce MP and coat protein. The exact mechanism by which virus moves throughout the plant is unknown but the interaction of plant pectin esterase with the viral movement protein (MP) has been implicated. The virus wrapped in the MP can infect adjacent cells. The viruses multiply within the cells and kill them. They are then released to infect new leaf or plant

Disease management :

The following are some measures that can be followed management of viral plant disease :

1. All tools should be decontaminated.
2. The disposal of the dead leaves and old plants as dry ToMV infected leaves carefully in order to prevent blowing off those leaves around houses as dust can infect healthy plants.
3. There should in increase in cultivation of virus resistant varieties.
4. The infected plant should be removed from the yield during growing season.

Disease caused by Algae :

Algal plant diseases which are found on land surface is called as chlorophyta. Theses are the minor type of plant disease which affects citrus species expect lime and lemon. The type of disease can be controlled and maintained through the use of easy methods.The plant diseases caused by Algae are :

1. A- Cephaloeuros spp which is genus of parasitic thalloid algae that causes red dust and grows superficially and damages trees.)
2. Gram-negative organisms like Alteromonas spp, Cytophaga spp,Flavobacterium spp, Pseudomonas spp, Pseudoalteromonas spp, etc also causes plant diseases.
3. The species likeSaprospira and Vibrio also mainly cause rot symptoms in plants.

Symptoms of Algal diseases :

The following are some symptoms of Algal plant disease :

• There will be the appearance of raised spots of varying color on the leaf surface.
• There will be the occurrence of fruit disfiguring and rotting of fruit.
• The death of new spots may occur.

Host :

Some host of Algal disease can be tea, coffee, mango, guava. etc.

The followings are some symptoms of Algal plant disease:

• The infected areas on twigs can be swollen and cracked.
• There may be the appearance of fuzzy round green spots that may turn Red-brown with time.
• There will little damage and appearance of raised lesions either on the surface of leaves.
• The chlorosis can be caused by those lesions which make leaf dry and leaves small depressions.
• These diseases mainly affect the trees, mainly on its branches and are visible on fruiting bodies.
• There may be the appearance of sunken, necrotic lesions of dark color.
• On the necrotic fruits lesions, dead twigs, inflorescence, and leaves ,conidia are produced.
• The flesh of fruits are affected and small sunken lesions are seen.

Diseases management :

The following procedures can be applied for its management :

• The algal disease in plants can be controlled by applying copper with the type of oil at the time of its late dormancy.
• The infected plant should be removed from the yield during growing season.
• The diseased parts can be trimmed
• The tools should be decontaminated.

Reference:

1. Alexander, M. Introduction to Soil Microbiology. Academic Press, 1961.
2. Rangaswami, G and Bagyaraja PT. Agricultural Microbiology. 2nd. Prentice Hall of India, 1993.
3. RM, Atlas and R Bartha. Microbial Ecology : Fundamental and Applications. The Benjamin Cummins Publication Co. Inc., 1998.