Blast disease of Paddy : Symptoms and Control Measures | Plant Pathology

In this article we will discuss about:- (1) Introduction to Rice Blast (2) Symptoms of Blast Disease (3) Control Measures of Blast Disease

(1) Introduction to Rice Blast 

Causal Organism : Pyricularia oryzae
Host: Oryza sativa L.

Rice (Oryza sativa L.) is the major staple food for nearly one half of the world’s population. It occupies an area of 156.7 million hectare, with a total production of 650.2 million tonnes in 2007. India has an area of over 44.0 million hectare under rice, producing -144.1 million tonnes of paddy in 2007.

Rice cultivation is the principal activity and source of income for about 100 million household in Asia and Africa (FAO, 2004). It is primarily a tropical and subtropical crop, but the best grain yields are obtained in temperate regions.

The rice crop suffer from a number of diseases among them rice blast caused by one of the most devastating agricultural pathogens in the world, a fungus called Magnapor the grisea (Hebert) Barr [anomorph: Pyricularia grisea (Cooke) Sacc.], is one of the most important, causing significant losses in yield. Rice blast was probably first recorded as rice fever disease in China in 1637.

It was later described as imochi-byo in Japan in 1704, and as brusone in Italy in 1828. The fungus is currently reported to be present in at least 85 countries. In 1996 rice blast was found in rice in California, and has since been found in grasses on golf courses in the mid-western United States.

It can also infect a number of other agriculturally important cereals including wheat, rye, Barley, and Pearl Millet causing diseases called blast disease or blight disease. M. grisea causes economically significant crop losses annually, each year it is estimated to destroy enough rice to feed more than 60 million people.

(2) Symptoms of Rice Blast:

Rice blast is caused by Magnaporthe grisea (Hebert) Barr. All the above ground parts of the plant can be attacked by the fungus at any growth stages. However, Seedling stage, rapid tillering stage after transplanting and flower emergence stage were identified as the most susceptible ones to blast.

The disease can be described based on the part of the plant infected as follow:

i. Leaf Blast:

On the leaves the lesion/ spots first appear as minute brown specks, and then grow to become spindle-shaped, pointed at both ends. The center of the spots is usually gray or whitish with brown or reddish-brown margin. Fully developed lesions reach 1-1.5 cm long, 0.3-0.5 broad. Under favorable conditions, lesions enlarge and coalesce; eventually kill the leaves.

ii. Collar Rot:

Infection at the junction of the leaf blade and sheath in the typical brown “collar rot” symptom. A severe collar rot can cause the leaf to die completely. When collar rot kill the flag or penultimate leaf it may have a significant impact on yield.

iii. Neck Blast:

This occur when the pathogen infect the neck of the panicle to cause a typical “neck rot” or rotten neck blast symptom. The infected neck is griddled by a grayish brown lesion and the panicle falls down if the infection is severe. If the neck blast occurs before the milk stage, the entire panicle may die prematurely, leaving it white and completely unfilled.

iv. Panicle Blast:

The pathogen also causes brown lesions on the branches on the panicles and on the spikelets pedicles, resulting in “panicle blast”. Infection of the neck, panicle branches, and spikelets pedicles may occur together or may occur separately.

v. Node Blast:

The fungus may also attack the stem at nodes, node blast in which the stem bend and break at the node causing spikelets sterility. Blast Symptoms of seeds themselves consist of brown spots, blotches.

(3) Control Measures

• Use of seeds from a disease free crop
• Grow resistant varieties like  MTU 1010, Swathi, IR 64, IR 36, Jaya, Vijaya, Ratna,
• Remove and destroy the weed hosts in the field bunds and channels.
• Split application of nitrogen and judicious application of nitrogenous fertilizers
• Treat the seeds with Captan or Thiram or Carbendazim or Carboxin or Tricyclazole  at 2 g/kg.
• Seed treatment with biocontrol agent Trichoderma viride@ 4g/kg or Pseudomonas fluorescens @ 10g/kg of seed.
• Avoid close spacing of seedlings in the main field.
• Spray the main field with Tricyclazole@0.06%.