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Diseases

Diseases
27
Jun

Causal Organism and Pre-disposing factors of Stem Rot

Causal Organism of Stem Rot    

  • The causal organism for Stem rot disease is Sclerotium oryzae Cattaneo

Predisposing factors of Stem Rot    

The predisposing factors for Stem rot disease are:

1. Presence of infected bodies or sclerotia in the upper soil layer or on irrigation water.

2. Presence of wounds as entry points of the fungus.

3. Panicle moisture content.

4. Nitrogen fertilizer application.

File Courtesy: 
DRR training manual (Dr. krishnaveni)
27
Jun

Symptoms of Stem Rot

The symptoms of Stem rot 

1. The first symptom appears as small, black irregular lesions on the outer leaf sheath near the waterline. 

2. The fungus penetrates the inner leaf sheath resulting the basal portion of the stem to rot.

3. Numerous black, round shining bodies (sclerotia) are formed on the affected sheaths stems, and also in the hollow internodes at maturity.

File Courtesy: 
DRR training manual (Dr. krishnaveni)
Photo Courtesy: 
DRR Training Manual
27
Jun

Economic importance of Stem Rot

 

The economic importance of the stem rot disease is

1. Cause heavy losses in many countries. For example, in Japan, 51,000 to 122,000 hectares infected and estimated annual losses of 16,000-35,000 due to this disease. In Vietnam, the Philippines.

2. India, losses from 30% to 80% was recorded.

 

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Distribution and occurrence of Stem Rot

 

The distribution and occurrence of Stem rot disease are as follows 

1. The infected bodies or sclerotia are found in the upper soil layer. They survive in air-dry soil, buried moist rice soil, and in tap water. 

2. They can also survive on straw, which is buried in the soil. The sclerotia float on irrigation water and infect newly planted rice during land preparation.

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Stem Rot (sclerotium oryzae)

Introduction:

1. Stem rot is caused by Sclerotium oryzae, which survive through pin-head size sclerotia in rice straw and the soil. 

2. It is an important disease particularly in water-logged areas. 

3. The sclerotia produced by the fungus serve as primary inoculum source by floating on the water and infecting rice stems of the healthy plant at the waterline.

4. Sclerotia form abundantly in infected tissues as the rice plant nears maturity and continue to develop in crop debris.

 

File Courtesy: 
DRR training manual (Dr. krishnaveni)
27
Jun

Management options of Narrow Brown Spot

 

Control measures of Narrow Brown Spot disease: 

1. Cultural practices, such as the use of potassium and phosphorus fertilizers, and planting of early maturing cultivars early in the growing season, could manage this disease effectively.

2. Use of resistant varieties is the most effective approach to manage the disease.

3. Resistant varieties and lines are grown only in United States and India.

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Causal Organism and Pre-Disposing factors of Narrow Brown Spot Disease

Causal Organism:

The causal  organism for  Narrow Brown Spot disease is Cercospora janseana (Cercospora oryzae).

Pre-disposing factors:

The predisposing factors for Narrow Brown Spot are 

1. Rice crops grown on problem soil deficient in potassium

2. Temperature ranges from 25-28° C

3. Varieties grown are susceptible 

4. Disease incidence occur at growth stage.

 

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Symptoms of Narrow Brown Spot

 

The symptoms which are developed Narrow Brown Spot disease: 

1. The short narrow, elliptical to linear brown lesions appear on leaf blades sometimes they may also occur on leaf sheaths, pedicels, and glumes and rice hulls.

2. Lesions are about 2-10 mm long and 1 mm wide

3. Lesions are narrower, shorter, and darker brown on resistant varieties.

File Courtesy: 
http://www.knowledgebank.irri.org
Photo Courtesy: 
DRR Training Manual
27
Jun

Economic Importance of Narrow Brown Spot

 

The economic importance of the Narrow Brown Spot disease: 

1. Narrow Brown Spot disease on severe infection causes premature death of leaves and leaf sheaths, premature ripening of kernels and lodging of plants. 

2. It decreases the market value of the grains because of grain discoloration and chalkiness, and also reduces the milling recovery.

3. Yield loss of 40% was reported due to the incidence of disease in Suriname during the 1953 and 1954.
 

 

27
Jun

Distribution and Occurrence of Narrow Brown Spot

1. The Narrow Brown Spot disease has been reported in several countries in Asia, Africa, Australia, and Papua Guinea.

2. The disease is observed on rice crops grown on potassium deficient soils.

3. Temperature ranging from 25-28° C is favorable for the growth of the disease.

4. Susceptibility of the variety to the fungus and the growth stage of the rice crop are factors decide the development of the disease.

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Narrow Brown Spot ( Cercospora janseana)

Introduction

1. The Narrow Brown Spot disease varies in severity from year to year.

2. It becomes more severe when rice plant attains maturity, causing premature ripening and yield reduction. 

3. Leaf spots are long (1/10 to 1/2 inch), narrow (1/32 inch), and cinnamon-brown.

4. Premature leaf death occurs in severe cases. Early maturing varieties tend to escape the major impact of the disease.

File Courtesy: 
http://165.91.154.132/Texlab/Grains/Rice/ricenbls.html
Photo Courtesy: 
Rice Blast Disease and its Management ( Dr . Krishnaveni)
27
Jun

Management options of Leaf Scald

Management Options  of  leaf scald  

The Leaf scald disease can be controlled by different means. Those are:

1. The only cultural control practice, which is applicable for the disease is to avoid use of high amount of fertilizer.

2. There are some cultivars from India with resistance to the disease.

3. Chemicals such as Benomyl, Carbendazim, Quitozene, and Thiophanate-methyl can be used to treat the seeds to eliminate the disease. 

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Predisposing factors of Leaf Scald

Predisposing factors of Leaf Scald:  

The predisposing factors for Leaf scald disease are:

1. High nitrogen

2. Wet weather - close spacing of plants

3. Wounded leaves - sources of infection such as seeds and crop stubbles

 

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Economic Importance and Symptoms of Leaf Scald

The economic importance of leaf scald disease: 

1. In India and Bangladesh, yield losses of 23.4% and 20-30% were reported respectively.

2. This disease has caused considerable losses in Latin America and West Africa.

The Leaf scald disease symptoms: 

1. Zonate lesions beginning at the leaf tip or margin has alternating bands of tan to gray with reddish brown forming a chevron pattern on the affected leaves. 

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Causal Organism, History, Distribution and Occurence of Leaf Scald

Causal Organism for leaf scald disease is Microdochium oryzae

History

  • In Andhra Pradesh the leaf scald disease was observed in 1981 in the Regional Agricultural Rice Research Station, Nellore.

Distribution and Occurance

1. The Leaf scald disease was observed in USA and West Africa.

2. Leaf scald appears to be very common in Latin America and in other parts of Asia

File Courtesy: 
http://www.knowledgebank.irri.org
27
Jun

Introduction to Leaf Scald (Microdochium oryzae)

 

1.The leaf scald disease has been reported worldwide in rice-growing regions (Farr et al. 2008) and seeds prove as the most important inoculum source.

2. The teleomorph stage, Monographella albescens V.O. Parkinson, Sivan. & C. Booth was recently reported in green and senescent leaves of rice crops close to ripening.

 

File Courtesy: 
http://www.publish.csiro.au/?act=view_file&file_id=DN08030.pdf
25
Jun

Stem Rot (Sclerotium oryzae)

Introduction to 

Stem Rot (Sclerotium oryzae)

1. Stem rot is caused by Sclerotium oryzae, which survive through pin-head size sclerotia in rice straw and the soil. 

2. It is an important disease particularly in water-logged areas. 

3. The sclerotia produced by the fungus serve as primary inoculum source by floating on the water and infecting rice stems of the healthy plant at the waterline.

File Courtesy: 
DRR training manual (Dr. krishnaveni)
25
Jun

Host plant resistance of Sheath blight

Host plant resistance of Sheath blight: 

Donors 

  • T 141
  • OS 4
  • Saibham
  • BCP 3
  • Saduwee
  • Bhujan
  • Remadja
  • Laka
  • Nangmons 4
  • Ta-Oo-Cho-Z
  • ARC 15368
  • Athebu Phourei  

 

File Courtesy: 
DRR training manual (Dr. krishnaveni)
25
Jun

Chemical control of Sheath blight

Chemical control of Sheath blight: 

A Spray of either validamycin 3 L @ 2.5 ml or 

  • Hexaconazole 5 EC @ 2.0 ml or
  • Thifluzamide 24 SC @ 0.75 ml or
  • Propiconazole 25 EC @ 1 ml or 
  • Thiophanate-methyl 70 WP or 
  • Carbendazim 50 WP @ 1.0 g / L of water will prevent the spread of the disease. 

 

File Courtesy: 
DRR training manual (Dr. krishnaveni)
25
Jun

Cultural practices to control Sheath Blight

Cultural practices for the control of Sheath Blight are: 

1. Closer plant spacing should be avoided; otherwise it develops a dense crop growth favorable for the horizontal spread of the disease.

2. Need-based or real-time or split application of nitrogen fertilizer is recommended in the fields with a high amount of inoculum.

3. Sanitation, specifically removing of weeds, help to control sheath blight because the pathogen also attacks weeds which are commonly found in rice fields. 

 

File Courtesy: 
http://www.knowledgebank.irri.org/ricedoctor/index.php?option=com_content&view=article&id=565&Itemid=2770
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