Plant disease caused by Protozoa, Nematodes and Parasites

The plant disease caused by Protozoa, Nematodes, and Parasites .

Diseases caused by Protozoa:

Flagellated protozoa cause a number of diseases of perennial crops often in phloem tissue. Example : Heart rot of coconut, wilt disease of coffee, wilt of palm, etc. The flagellates may be even be transmitted by insect vectors. Example : Transmission of the Phytomonas spp.

H(E)ART ROT OF COCONUT :

Classification :

Domain : Eukaryota

Kingdom : Protista

Phylum : Protozoa

Subphylum : Sarcomastigophora

Order : Kinetoplastida

Family : Trypanosomatidae

Genus : Phytomonas

Species : phytomonas staheli

Host :

The host of protozoal plant disease is Coconut (Cocus nucifera ), African oil palm (Elaeis guineensis )

Pathogen :

Phytomonas staheliis the pathogen which causes protozoal plant disease. The pathogens in the infected plants are elongated promastigotes (15-20×1.5 -2 )µm. The pathogens have a single flagellum at the anterior end. Kinetoplast is situated at the base of the flagellum, anterior to the nucleus.

The pathogen is widely distributed in South American countries and Caribbean islands and Africa.

Transmission :

It is transmitted by the process of Vector transmission, where the vector is Lincus spp (Hemipteran ) .

Symptoms :

The following are of disease caused by the protozoa in plants are :

1. The diseases start with the browning of older leaves and progresses to the younger ones starting at the tip.
2. The flowers turn black and rusty.
3. The younger fruits turn brown, shrink, rot and fall while the ripe fruits do not seem to be affected.Roots and spears rot with crown rot secondarily infected by opportunistic fungi and bacteria.
4. The death of coconut within 2-3 months of onset of symptoms by rotting the heartwood of the coconut.
5. The major characteristics are rotting of the heart and hence the for the disease h(e)art rot.

Prevention and Control :

The following are some measures for prevention and control of plants from protozoa :

1. The use of insecticides for vector control.
2. Proper sanitation should be maintained and the process of crop rotation can be done.
3. Plants can also be prevented by host eradication and improvement of crop environment.

Diseases caused by Nematodes :

Root-knot of Rice plants:

Pathogen:

TheMeloidogyneor root knot nematodes are the plant parasitic nematodes. They exist in the soil in areas with hot climate or short winters. Root-knot nematodes (larvae) causes the development of root-knot and infect the plant root that absorbs the plant nutrients. Infection of the young plant is lethal while the mature plants decrease yield.

Classification :

Kingdom : Animalia

Phylum : Nematoda

Class : Secernentea

Order : Tylenchida

Family :Meloidogynidae

Genus : Meloidogyne

Species :graminicola

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Fig: Structure of Meloidogynegraminicola

Host :

Its host is Rice plant (Oryza sativa)

Habitat :

Meloidogyne graminicolais found in upland soils,deep and shallow flooded soils. These nematodes exist in unisexual form i.e. having both male and female .

Male:

Males have cylindrical, vermiform, tapering body structure more towards the anterior than posterior extremity.

Female:

Females are pearly white and have globular to the pear-shaped body with the small neck. Its cuticle is distinctly annulated. It's lip region is smooth, anteriorly flattened and not distinctly set off from the neck. It has stylet slender and is delicate and knobs are rounded with posteriorly with anterior margins. It has two ovaries which are well developed and convoluted and its body cavity is filled and overlying the intestine. It has developed uterus with several eggs.

Second stage juveniles:

In this stage , its body is in cylindrical form which is vermiform and tapering towards the posterior extremity. Its cuticle is finely marked.

Symptoms:

The followings are symptoms of Meloidogyne graminicola , which are described as follow:

1. The plants are uprooted and swellings and galls throughout the root system occurred.
2. Infected root tips are swollen and hooked, which is special characteristics of nematodes.
3. It can cause severe growth reduction and known to cause serious damage to deepwater rice.
4. The symptoms involve the typical stunting and chlorosis of young plants.
5. The submerged plants with serious root galling, do not emerge above the water level and die during the flooding.

Signs :

Its signs on different parts of plant is characterized as follow:

1. Roots: There is reduced root system with the development of galls at the tip.
2. Seeds:There grains were empty.
3. Whole plant : The plant seems to be dwarfed.

Life cycle :

Meloidogyne graminicola has a very short life cycle on rice of less than 19days at temperatures of 22-29^.C in Bangladesh. In India, the life cycle ofMeloidogyne graminicola is reported to be 26-51 days at 26*C , depending on the time of year (19-51 days). An isolated from the USA completed its cycle in 23-27days at 26*C.

Infective, second-stage juveniles of Meloidogyne graminicola invade rice roots just behind the root tip in upland conditions . Females develop within the root and it laid eggs mainly l in the cortex. Juveniles can remain in the maternal gall or they migrate through the parenchymatous tissues of the cortex to new feeding sites within the same root intercellularly.

The second stage Juvenile (J-2) migrate intercellularly establish a feeding site in the zone of differentiation of vascular cylinder and develop into swollen females. During this, some cells become hypertrophied with intense cellular multiplication (hyperplasia) leading to the giant cell and gall formation.

Methods of disease management:

1. The increasements in soil fertility can compensate for some damage by Meloidogyne graminicola.
2. The chemical control on the field scale is generally uneconomic, particularly with low-yielding upland rice.
3. The cultivation of resistant varieties is one of the effective methods.
4. Crop rotation can be done.
5. Certain crops are resistant or poor hosts of Meloidogyne graminicola and nematode populations could be reduced using rotation of crop,(example : castor, cowpea, sweet potatoes, soybean, soybeans, sunflower, sesame, onion, turnip, jute, and okra.)

Diseases caused by Parasitic plants:

Broomrape disease of Tobacco (Nicotiana tobaccum)

Pathogen :

The parasite causingBroom rape disease of Tobacco is Orobanche ramosa /Phelipancheramosa / Branching broomrape.

Classification :

Domain : Eukaryota

Kingdom : Plantae

Phylum : Spermatophyta

Subphylum : Angiospermae

Class : Dicotyledonae

Order : Scrophulariales

Family : Orobanchaceae

Genus :Orobanche

Species :Orobanche ramosa

Host and Distribution :

Tihs is a parasitic plant in agricultural fields, infesting crops including tobacco. potato and tomato. Orobanche ramosa occurs naturally in Mediterranean countries in southern Europe, Africa, and the Middle East, extending eastwards to India, Pakistan and China.

Pathogen characteristics :

Some characteristics of are as follow:

1. It is an annual, broad-leaved, herbaceous and parasitic and about 10-60 cm tall and is recognised by yellow-straw colored stems that lack chlorophyll.
2. The stem is usually very branched bearing alternate scales.
3. Its root system is less developed whose stem base is below the ground and normally swollen and tuberous.
4. The leaves are merely triangular with alternating scales and its seeds are small black to brown color.
5. A single plant carries hundreds of flowers and hence produces numerous seeds.

Symptoms:

The followings are symptoms of diseases caused inOrobanche ramosa in plants :

1. It causes the wilting, necrosis and yellowing of the foliage and plant gets weakened.
2. There is the reduction in fruit production and effects in its germination also.
3. The early senescence of the whole plant occurred.
4. The seedlings have root-like growth which gets attached to roots of the nearby host.

Controlling and diseases management:

• Use of herbicides like Propyl butyl ethyl carb mo thioate can be used against plant parasites.
• Proper sanitation should be maintained and the process of crop rotation can be done.
• Plants can also be prevented by host eradication and improvement of crop environment.

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.