Rice blast

Primefact number Edition Published Author
1211 Third Jul 2017 Plant Biosecurity and Product Integrity

Green rice leaves with white patches that have brown edges

Rice stem with brown and rotting leaf sheath

Rice stems with brown and rotting patches located at the node

Rice stems with brown rotting patches in the middle of the stem

Rice panicle with greyed florets and brown lesions on panicle branches

Rice blast is considered the most important disease of rice worldwide.

Rice blast is present in the tropical wetlands of northern Australia. In 2011 rice blast was found on a rice crop in northern Western Australia.

Rice blast is a fungal disease caused by Magnaporthe grisea. This fungus is also called Pyricularia grisea.

Rice blast (Magnaporthe grisea) is an exotic plant pest not present in the New South Wales Rice Biosecurity Zone PNG, 339.73 KB. This disease is a serious threat to Australia’s rice industry.

Notifiable status

Rice blast (Magnaporthe grisea) is a notifiable plant disease in NSW.

All notifiable plant pests and diseases must be reported within 1 working day.  You can report notifiable plant pests and diseases by one of the following methods:

A full list of notifiable plant pests and diseases can be found in Schedule 2 of the NSW Biosecurity Act 2015.

Symptoms

Rice blast spores can infect plants at all growth stages, from seedlings to maturity. Symptoms develop on all above ground plant parts.

Lesions or spots are the most common symptom. Lesions are usually 1-1.5 cm long and 0.3-0.5 cm wide.

Leaf blast

Leaf lesions start as small white, grey or blue-tinged spots. Under moist conditions lesions enlarge quickly to either oval or diamond-shaped spots or to linear lesions with pointed ends, grey or white centres and narrow brown borders (Figure 1).

Severe infections may lead to death of leaves and whole plants. Leaf blast infections provide inoculum for panicles to become infected.

Collar rot

If a rice blast lesion is located at the junction of the leaf blade and leaf sheath the entire leaf can be killed. The leaf collar lesion discolours to brown and the leaf blade dies (Figure 2).

Node infection

Infected nodes appear black-brown and dry (Figure 3). An infection at the node often results in the stem breaking.

Neck rot

Neck rot may result in death of an entire panicle (Figure 4). Symptoms appear at the base of the panicle, starting at the node. The tissue turns brown and shrivels causing the stem to snap and lodge.

Panicle blast

Panicles which do not break or fall off as a result of neck rot may turn white to grey. Partially infected panicles may show grey-brown lesions among the panicle branches and on the stems of florets. Florets which do not fill turn grey (Figure 5).

Hosts

Rice (Oryza sativa) is the main host of rice blast. Although the fungus can live on many grass plants.

Disease cycle

The rice blast pathogen overwinters as fungal strands or spores on diseased rice stubble or seed or in living plants.

Infection in a new season may originate from the fungus overwintering on rice straw.

Rice blast spores are transported by wind and water and can infect rice plants after landing on them. Many infection cycles may occur within a cropping season if weather conditions are favourable.

Actions to minimise risks

Put in place biosecurity best practice actions to prevent entry, establishment and spread of pests and disease:

  • practice “Come clean, Go clean”
  • ensure all staff and visitors are instructed in and adhere to your business management hygiene requirements
  • source propagation material of a known high health status from reputable suppliers
  • keep records