Xanthomonas oryzae pv. oryzae is a bacterium which causes a serious blight of rice

Rice

Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...

, other grasses and sedge

Sedge

- Plants :* Acorus calamus, sweet flag, a plant in the Acoraceae family* Any of the plants in the family Cyperaceae- Animals :* A collective noun for several species of birds, including bitterns, cranes and herons* Sedge-fly, caddisfly- Other uses :...

s.

Background

The genus Xanthomonas

Xanthomonas

Xanthomonas is a genus of Proteobacteria, many of which cause plant diseases. Most varieties of Xanthomonas are available from the National Collection of Plant Pathogenic Bacteria in the United Kingdom and other international culture collections such as ICMP in New Zealand, CFBP in France, and...

, which mostly comprises phytopathogenic bacteria, is a member of the family Pseudomonadaceae

Pseudomonadaceae

The Pseudomonadaceae is a family of bacteria that includes the genera Azomonas, Azomonotrichon, Azorhizophilus, Azotobacter, Cellvibrio, Mesophilobacter, Pseudomonas , Rhizobacter, Rugamonas, and Serpens...

. Among xanthomonads, Xanthomonas oryzae pv. oryzae causes bacterial blight (BB) of rice which is one of the most important diseases of rice in most of the rice growing countries.

Bacterial blight of rice has high epidemic potential and is destructive to high-yielding cultivars in both temperate and tropical regions especially in Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

. Its occurrence in the 70s in Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

 and the Americas has led to concerns about its transmission and dissemination.

Research on bacterial blight of rice was commenced in Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 as early as in 1901, and the efforts were focused mainly on ecological studies and chemical control. Since then, significant gains have been made in understanding BB through analysis of the interactions between X. oryzae pv. oryzae and rice at many levels, including studies focused on the epidemiology, population biology, physiology, cell biology, biochemistry, and molecular genetics of the host pathogen interaction. It is very notable that BB became the first case where the genome sequencing of both host plant and pathogen was completed.

Hosts

There is a very large host range for Xanthomonas oryzae pv. oryza.

Among the grasses, hosts include:

• Cenchrus ciliaris (buffelgrass)
• Cynodon dactylon
  Cynodon dactylon
  Cynodon dactylon , also known as Dūrvā Grass, Bermuda Grass, Dubo, Dog's Tooth Grass, Bahama Grass, Devil's Grass, Couch Grass, Indian Doab, Arugampul, Grama, and Scutch Grass, is a grass native to north and east Africa, Asia and Australia and southern Europe...
  
  (Bermuda grass)
• Echinochloa crus-galli
  Echinochloa crus-galli
  Echinochloa crus-galli is a type of wild grass originating from tropical Asia that was formerly classified as a type of panicum grass. It is commonly known as Cockspur , Common Barnyard Grass, or simply "barnyard grass"...
  
  (barnyard grass)
• Leersia hexandra (southern cut grass)
• Leersia oryzoides
  Leersia oryzoides
  Leersia oryzoides is a species of grass known by the common name rice cutgrass. It is a widespread grass native to Europe, Asia, and North America and present in many other regions, such as Australia, as an introduced species. This is a rhizomatous perennial grass growing to a maximum height...
  
  (Rice cutgrass)
• Leptochloa chinensis (Chinese sprangletop)
• Oryza
  Oryza
  Oryza is a genus of seven to twenty species of grasses in the tribe Oryzeae, within the subfamily Bambusoideae, native to tropical and subtropical regions of Asia, Northern Australia and Africa...
  
  (species of rice), including
  • Oryza sativa
    Oryza sativa
    Oryza sativa, commonly known as Asian rice, is the plant species most commonly referred to in English as rice. Oryza sativa is the cereal with the smallest genome, consisting of just 430Mb across 12 chromosomes...
    
    (rice)
• Panicum maximum (Guinea grass)
• Paspalum scrobiculatum
  Paspalum scrobiculatum
  Paspalum scrobiculatum is a member of the family Poaceae, commonly called Koda Millet, Kodo Millet or Kodra Millet. It is known as varaku/karuvaraku in Tamil...
  
  (ricegrass paspalum)
• Poaceae
  Poaceae
  The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...
  
   (Meadow grasses)
• Urochloa mutica (Tall panicum)
• Zizania aquatica (Annual wildrice)
• Zizania palustris (Northern wild rice (USA))
• Zoysia japonica (zoysiagrass)

Among the Cyperaceae (Sedges), hosts include:

• Cyperus difformis
  Cyperus difformis
  Cyperus difformis is a species of sedge known by several common names, including variable flatsedgeand smallflower umbrella-sedge. This plant is native to southern Europe, most of Africa and Asia, and Australia, and it is naturalized in other areas of the world, including large parts of the...
  
  (Small-flowered nutsedge)
• Cyperus rotundus
  Cyperus rotundus
  Cyperus rotundus is a species of sedge native to Africa, southern and central Europe , and southern Asia. The word cyperus derives from the Greek "κύπερος" and rotundus is from Latin, meaning "round"...
  
  (Purple nutsedge)

Symptoms

Symptoms appear on the leaves of young plants as pale-green to grey-green, water-soaked streaks near the leaf tip and margins. These lesions coalesce and become yellowish-white with wavy edges. The whole leaf may eventually be affected, becoming whitish or greyish and then dying. Leaf sheaths and culms of more susceptible cultivars may be attacked. Systemic infection results in wilting, desiccation of leaves and death, particularly of young transplanted plants.

In older plants, the leaves become yellow and then die. In its advanced stages, the disease is difficult to distinguish from leaf blight caused by Xanthomonas oryzae pv. oryzicola, but lesion margins are wavy rather than linear as for the former. Damage is often associated with lepidopteran leaf rollers, leaf-folders and hispa beetles, since bacteria readily enter the damaged tissue caused by insect infestation.