Rice blast is one of the most damaging diseases of rice, caused by the fungi Magnaporthe oryzae and Pyricularia oryzae. It was first recorded in China in 1637 and Japan in 1704. The disease affects 85 rice producing countries worldwide and can destroy enough rice to feed 60 million people. Symptoms appear on all above-ground parts of the rice plant and include lesions on leaves, stems, panicles, and seeds. Resistance to rice blast is conferred by major resistance genes and quantitative trait loci, but new virulent pathogen strains emerge over time. Management strategies include growing resistant varieties, crop rotation, removal of residue, balanced fertilization, and fungicide application.

1. By:
Jeevan Kumar Shrestha
National Chung Hsing University
Jeevan@smail.nchu.edu.tw
Academia Sinica, Taipei, Taiwan
as0202092@gate.sinica.edu.tw

2.  One of the most damaging diseases of rice
 This disease was first known as rice fever
disease in China as early as 1637
 Disease of rice blast first recorded in 1704,in
Japan
 The causal organism was first detected by
Cavara in 1891from Italy
 Reported from 85 rice-producing countries or
regions worldwide
 Destroy rice that can feed 60 million people

3.  Blast severely affects lowland rice in
temperate and subtropical areas of Asia, and
is highly destructive to upland rice in tropical
areas of Asia, Latin America, and Africa
(www.irri.org)
Countries affected by rice blast (Wang et al., 2014)

4. Rice blast diseases is caused by Magnaporthe oryzae &
Pyricularia oryzae.
M. oryzae is an ascomycete fungus.
Reproduce both sexually and asexually
Survive in seeds, plant residues and weeds
Optimum Relative Humidity. – 90%
Optimum Temperatue – 20-25° C
Toxin – Pyricularin & ά– Picolinic acid
Spores of M. oryzae

5.  Eleusine coracana (finger millet)
 Hordeum vulgare (barley)
 Leersia hexandra (southern cut grass)
 Lolium multiflorum (Italian ryegrass)
 Lolium perenne (perennial ryegrass)
 Oryza glaberrima (African rice)
 Oryza longistaminata (perennial wild rice)
 Oryza sativa (rice)
 Triticum aestivum (wheat)

6. (Wilson & Talbot, 2009)

7.  Symptoms occur in all above ground parts of the
rice plant at all growth stages
 Infected roots have also been
observed
 Seeds display brown spots
after infection

8. 1. Leaf Blast (seedling to tillering stage)
Small to spindle‐shaped spots with
brown border and gray center
Dimension is 0.4-0.8mmx0.1-0.2mm
Spots join resulting in drying and
death of leaves
2. Collar blast (tillering stage)
 Entire leaf blade dries up when the base
of the flag leaf is infected

9. 3. Panicle blast (booting to heading)
 Dark necrotic lesions that partially
or completely cover the panicle base,
or the uppermost internode,
or lower panicle axis
4. Node blast (tillering stage)
 Node of the stem turns
blackish and breaks
easily

10.  Complete genetic resistance (vertical resistance) is
conferred by major blast R genes named as
Piricularia genes or Pi-genes. (Wang et al., 2014)
 Incomplete resistance (horizontal resistance) is
often conditioned by more than one gene on
different chromosomal regions. These genes
referred to as quantitative resistant loci (QTLs) .
(Wang et al., 2014)
 During interactions between rice and blast
pathogens, products of the R gene can specifically
recognize the corresponding elicitors of M. oryzae.
 All R genes have been mapped on all rice
chromosomes except for chromosome 3

11.  Host resistance is the most economical and
environmentally friendly way of disease control.
 Physiological races and variation in
pathogenecity of M. oryzae were first reported by
Sasaki in Japan as early as 1922(Sasaki, 1992)
 Variation in pathogenicity of the blast fungus
have been attributed : mutations, sexual
hybridisation, parasexuality and heterokaryosis
 Rice cultivars containing only a single R gene to a
specific pathogen race often become susceptible
over time due to the emergence of new virulent
races

12.  Rice blast is known to cause approximately 60%
-100% yield losses (Kihoro et al., 2013)
 Threatens food security (Pennisi, 2010)
 Increase in the production cost and consumar
price
 Environmental degradation due to the continuous
use of pesticides
 Farmers are shifting into horticultural crops and
livestock rearing

13.  Presence of the blast spores in the air
throughout the year
 Upland rice environment
 Cloudy skies, frequent rain and drizzles
 High nitrogen levels
 High relative humidity
 Low soil moisture
 High leaf wetness or dew period

14.  Disease resistance cultivar- IR 64, , Jin 23B,
CO39, IR50, Pusa1602 and Pusa1603
 Crop rotation
 Removal of crop residue from field
 Use healthy seed and planting materials
 Early sowing of seeds just after onset of rainy
season
 Seed to a stand of 15 to 20 plants per square
foot.
 Removal of weeds (ROUGING)
 Use balance fertilizers – no heavy use of N2

15.  Commonly used blasticides:
 isoprothiolane, probenazole, pyroquilon, tricyclazole etc.
 Broad spectrum fungicide: azoxystrobin
 First spray - tillering stage
 Second spray – flowering stage
 Seed treatment – Tricyclazole or Beam 75 WP (4 gm/ kg
seed)
 Biological control:
 Pseudomonas fluorescens strain Pf1

16.  International Rice Research Institute-Rice Knowledge Bank. IRRI: Crop
Health, Disease: Rice Blast.
http://www.knowledgebank.irri.org/ipm/rice-blast/symptoms.html
 Kihoro J, Bosco NJ, Murage H, Ateka E & Makihara D. Investigating the
impact of rice blast disease on the livelihood of the local farmers in
greater Mwea region of Kenya. SpringerPlus 2013, 2:308
 Pennisi E. Armed and dangerous. Science. 2010;327:804–805.
 Pinoy Rice Knowledge Bank. Rice Blast. http://www.pinoyrkb.com
 Sasaki R. Extensive of strains in rice blast fungus. Journal of plant
protection 1992; 634-644
 Wang X, Lee S,Wang J, Ma J, Bianco T, Jia Y.Current Advances on Genetic
Resistance to Blast Disease. Rice-Germplasm, Genetics and Improvement
2014; 195-208.
 Wilson RA, Talbot NJ. Under pressure: investigating the biology of plant
infection by Magnaporthe oryzae. Nat Rev Microbiol, 7 (2009), pp. 185-
195