Bakanae Disease Of Rice

Bakanae Disease of rice is caused by a fungus and the scientific name of the fungus is Fusarium moniliforme ( it is the imperfect stage of the fungus ) or Gibberella fujikuroi ( it is the perfect stage of this fungus ).

Bakanae disease has a background history. Bakanae disease was first identified in Japan by Shotaro Hori in 1898. Shotaro Hori saw that some rice plant elongated abnormally. This rice plants produced no edible grains that means empty panicles. Also this rice plants was not capable to support them due to their abnormal and excessive. As a result stems of those rice plants  break down at last died. So Shotaro Hori called them Bakanae ( ba-ka-na-eh ). The meaning of Bakanae is ''foolish seedling of rice''. But this disease is very common in North America, Africa and Asia.
The main reason of abnormal elongation of rice plants is that in perfect stage ( Gibberella fujikuroi ) the pathogen produces a growth hormone named gibberellic acid into the host tissues. Before it was thought that Bakanae was a disease of rice seedlings but now Bakanae disease is observed in young to mature plants throughout the growing season. This disease is observed from nursery or seed bed to main crop field.

Symptoms:
This disease is seen in the main fields and also in the seed beds. In the seed bed the infected rice seedlings become very thin ans sick. Seedling s become pale to light green in color where other seedlings are normal green in color. Seedlings are also abnormally elongated than other seedlings. So sometimes wilt is occurred in seedbed among the infected rice seedlings finally seedlings die. If infected seedlings are transplanted in the main field, seedlings dry up and finally die. The most conspicuous symptoms is seen in the main crop fields. Infected rice plants become tall. Stray and  abnormally elongated tillers are appeared in the field. Sometimes adventitious roots are develop from the first or second or third node of the infected rice plants. Whitish and pinkish masses of spore are produced the pathogen in the infected host tissue. Flowers also develop earlier in infected field grain set-up is not occurred. Plants ( infected ) die before maturation of flower. Plants that are infected at collar region, died within two to six months.

Systematic position of the pathogen:
Division: Eumycota
Subdivision: Deuteromycotina
Class: Hyphomycetes
Order: Moniliales
Family: Tuberculariaceae
Genus: Fusarium
Species: Fusarium moniliforme

Control or management of Fusarium moniliforme
1. We must cultivate the varieties that are resistant to Bakanae disease.
2. We must seeds from disease free plants and area.
3.We must uprooted and than burn the infected plants immediately.
4. Stubble that remain after harvesting crops should be destroy by burning because pathogen may stay in the stubble of plant parts.
5. Field should be dried immediately when disease in the field.
6. Seed may be treated with Provax 200 at the rate of 3g per kg before sowing.

Brown Spot Disease Of Rice

Brown spot of rice is caused by the pathogen named Bipolaris oryzae ( imperfect stage ) or ( Cochliobolusbolus miyabenus ( perfect ). This fungus can infect both mature rice plant and seedlings of rice. This disease has great economic importance because Bengal Famine was occurred in 1942 and 2 million people died in that area due to yield loss of 60- 90%.

There are so many collateral host of this fungus. They are Cynodon dactylon, Digitaria sanguinalis, Setaria italica, Leersia hexandra, Pennisetum tyhoides, Echinochloa colona etc.


If there are relative humidity more than 90%, it is a cloudy day, temperature range is between 25 degree to 35 degree, we must be careful in that day. Because those are favorable condition of this pathogen. In this time, if we apply high N- fertilizer, it will give extra advantage to the pathogen. Mainly this pathogen or fungus disseminated by wind. So must be careful, so that we can protect our rice plants.

Collateral host, stubble or straw of rice and seeds are the main source of inoculation of this fungus.

Symptoms:

Major infestation is seen on the leaf of plant. It also attacks glumes, coleoptiles, leaf sheath and seedling. It causes blight of seedling when it attack at seedling stage. Colors of the spots on the leaves is brown ( that is why the name of the disease is brown spot of rice ), shape is round to oval and size is 0.5 mm to 2 mm wide and 2 mm to 5 mm in length. At first spots are separate from each other but at later they may coalesce and become large. The coalesce spots form a large patches on leaves ( it is one of the characteristic symptoms ) of withered tissue. The middle or central part of the spots are gray or pale or dirty white in color and the margin of the spots are dark brown in color ( it is one of the characteristic symptoms ). In some leaves yellow halos are found in the center of the spot. At later whole leaf become yellow and dry. When grains are infected, grains become dark brown to black in color and later grains are shriveled.

Description of the Bipolaris oryzae:
Mycelium of this fungus grayish black in color. Mycelia are septate and branched. It's conidiophore is brown in color and remain as straight or slightly curved. Conidia are usually curved and tapering towards the end. Mycelium are germinate from two end of the conidia. So this fungus are belong to the Bipolaris Genus.

Disease cycle:
Though this disease disseminated by wind, it overwinters around the affected field. Different weeds are host collateral host of this pathogen. This fungus also overwinters into the infected seeds and stubble that remain in the field after harvesting crops. At first symptom is seen on the coleoptiles. On the collateral host conidia is produced by the fungus and spread through wind and this conidia cause secondary to the rice plant. At favorable condition conidia start to germinate and penetrate to the host tissue. After 3-4 days of infection symptoms are shown on leaves.

Systematic position:
Division: Eumycota
Sub-division: Deuteromycotina
Class: Hypomycetes
Order: Moniliales
Family: Dematiaceae
Genus: Bipolaris
Species: Bipolaris oryzae 

Management:
prevention measure
1. We must apply balance fertilizer for insuring the proper crop nutrition.
2. We should avoid water stress condition.
3. Also good drainage system is needed.
4. We must use healthy seeds for seedling.
5. We must avoid excessive use of N fertilizer.
6. Field should be weed free and stubble free.
7. We may cultivate brown spot disease resistant variety.
8. During preparation of seed bed we should prefer wet seed bed becacuse in dry seed bed pathogen is higher in dry seed bed than wet seed bed.

chemical control
Seed should be treated by dithane M-45 or Provex 200 at the rate of 2.5 g per kg of seeds.
Chemical control is done due to severe attack of the pathogen. But we must apply fungicide after taking the suggestion of the government agricultural officer. Cu fungicide like Cupravit is very effective and can control the disease.

Blast Disease Of Rice

There are 30 major fungal disease in world and blast disease of rice major one.
This disease is caused by a fungus. This fungus has perfect form and imperfect form. Pyricularia oryzae is it's imperfect form and Magnaporthe grisea is it's perfect form.

Symptom of Blast Disease of Rice
This fungus like to attack at the aerial portion of the rice plant. It can attack rice at any growth stage. The symptom is shown at leaves, nodes, and panicles ( sometimes in grain ) as spots or lesions. At first small spots are seen on the leaf. The color of the spots are bluish or light grayish. This spots are look like water-soaked. Spots may round or oval in shape. When the size of spot increases, the spot take spindle shape gradually. Margin of the spot becomes brown and middle becomes gray or white in color. Several spots coalesce and a large spot is formed. Nodes and glumes also attacked by this pathogen and symptoms also appeared on this organ. In infected node black lesions are seen and rings are formed. Finally this not break down and causes yield  loses. Brown or black spots are seen on the neck of the panicle when panicle is infected.

pathogen infected leaf

If we study the pathogen under microscope, we can mycelium, conidiophore and conidia. Mycelium of this fungus is thin, hyaline and septate. Conidiopore also septate and thin but light brown in color. Long conidiophore nay remain in single or in tufts. Conidia is hyaline to pale brown in color, smooth, generally 3 celled and pyriform.

Systematic position:
Division: Eumycota
Subdivision: Deuteromycotina
Class: Hyphomycetes
Family: Dematiaceae
Genus: Pyricularia
Species: Pyricularia oryzae

Disease cycle of Pyricularia oryzae:
Several grasses such as Digitaria marginata, Panicum repens, Brachiaria mutica etc are the shelter of this pathogen. This pathogen's mycelium and conidia also overwinters on straw piles or in the infected seeds for two years when dry condition is present. Conidia spread through wind and fall onto leaf. If water is deposited on the leaf, conidia germinate there. By germ tube pathogen penetrates into leaf through stomata. Then symptoms are shown. Gradually grains are infected. Then conidia released with droplets of water and take shelter in crop residue.

Magnaporthe grisea

Management:
We must  use healthy seeds for rice cultivation.
We must use resistant varieties.
We may supply 100 kg K fertilizer per hectare at the of soil preparation. 

Chemical treatment:
We must take suggestion of government agricultural officer before using any fungicide.
Seeds may be treated with provax 200 @ 0.3 % before seed sowing.
When field is infected fungicide may be used to reduce yield lose.

Some fungicide:
Cupravit, Benlae, Bavistin etc