Diseases of rice - Blast

1. Diseases of Rice
Bacterial Diseases Viral Diseases
Fungal Diseases
Bacterial Leaf Blight
Bacterial Leaf Streak
Bacterial sheath brown rot
Blast (Leaf and Collar)
Sheath Blight
False Smut
Brown Spot
Sheath Rot
Rice grassy stunt
Rice ragged stunt
Tungro

2. Blast
• Caused by Magnaporthe oryzae (Hebert) Barr is one of
the most damaging diseases of rice.
• The most common symptoms in commercial rice fields
induced by M. oryzae can be found on all the above
ground parts of the rice plant at all growth stages.
• Typically blast lesions are diamond shaped.
• Initial lesions appear dark green or grey with brown
borders; while, older lesions are light tan with necrotic
borders.
• Under favorable conditions, lesions can merge together
and rapidly enlarge to several centimeters in length,
eventually killing the leaf, and ultimately resulting in
plant death.
• Spores produced at the end of the growing season may
result in collar blast and neck blast; neck blast often
causes direct crop loss

3. Life cycle of Blast
• Mycelium and conidia on diseased straw and infected
seeds are the principal sources of primary infection.
• The fungus can attack a number of cereal and grass
hosts which could be important source of primary
infection. When several crops of rice are taken in a year,
the pathogen maintains a continuous disease cycle on
the rice crop itself.
• Under favorable conditions, the conidia can produce
symptoms within 4–5 days of infection.
• Conidia are produced on the lesions 6–7 days after
infection and disseminated by wind.
• A typical leaf blast lesion produces 2000–6000 conidia
each day for about 14 days. The rate of sporulation
increases with increase in relative humidity, while
release and flight of spores increase with enhancement
in dew period and wind speed, respectively.
(Laha et al., 2017)

4. Distribution and economic losses by Rice blast
• Average losses in the range of 10–30 % although
regional epidemics can be more devastating (Dean et al.
2012) resulting in grain yield loss up to 100 %.
• Severe yield losses due to blast have been reported in
different African countries ranging from 36 to 63 % in
Burkina Faso, 35–50 % in Nigeria, 20–30 %in Benin, 64 %
in Togo, up to 80 % in Sierra Leone and Cote d’Ivoire and
up to 100 % in Ghana and Gambia (Sere et al. 2013).
Worldwide distribution of rice blast disease. Red
dots show the countries or regions where blast
disease has been reported.
(Wang et al., 2014)
(Laha et al., 2017)

5. Genetic map of blast resistance genes on different rice chromosomes
0
5
10
15
20
25
1 2 3 4 5 6 7 8 9 10 11 12
No.
of
R
genes
Chromosomes
Major R genes mapped Minor R genes mapped R gene cloned
Chromosome position in Centimorgan ; The underlined words indicate either SSR or RFLP markers (Wang et al., 2014)

6. List of cloned blast resistance genes
(Ning et al., 2020)

7. • Blast R genes are predicted to play important roles in the frontier of rice defense responses.
• During interactions between rice and blast pathogens, products of the R gene can specifically
recognize the corresponding elicitors of M. oryzae. Since the Pia gene, identified in 1967 by
Kiyosawa as the first blast R gene from the japonica variety Aichi Asahi, 99 blast R genes have
been identified; in which 45% were found in japonica cultivars, 51% in indica cultivars, and the
rest 4% in wild rice species.
• Most deployed R genes have often been identified in Asian cultivated rice, specially rice
cultivars from Japan and China, with the exception of Pi9, Pi54rh, Pi40(t), and Pirf2-1(t), which
were domesticated from O. minuta, O. rhizomatis, O. australiensis, and O. rufipogon,
respectively. All R genes have been mapped on all rice chromosomes except for chromosome 3
• Among them, three major R gene clusters have been well characterized: the Piz locus on
Chromosome 6, the Pik locus on Chromosome 11, and the Pita locus on Chromosome 12.
Resistance genes and resistance genes clusters for blast resistance

8. Rice innate immunity signaling pathways triggered by M. oryzae
(Meng et al., 2019)

9. A, Breeding strategies for improving blast resistance in the previous studies. B, Breeding strategies that
have been used. C, Novel breeding strategies that can be utilized in further research.
Molecular breeding strategies using rice blast resistance genes
(Ning et al., 2020)