Oryza australiensis

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Oryza australiensis (Australian wild rice)

Oryza australiensis is a wild rice from tropical, monsoonal northern Australia. Also called Australian rice, it is a perennial grass that grows from rhizomes and uses the C3 photosynthesis pathway. It is notable for its resistance to many environmental stresses, especially heat, and it has the largest genome in the Oryza genus.

Appearance and growth
- It is a slender wild relative of cultivated rice, with tall, straight stems 0.8 to 2.5 meters high.
- The flowering panicle is open to partially contracted and 13 to 45 cm long.
- Leaves are grey-green to dark green; grains are long and the cooked grain tends to be non-sticky due to high gelatinization temperature and amylose content.
- It has higher protein content than many cultivated rices.
- Lemmas have awns ranging from 10 to 60 mm.

Habitat and ecology
- Found in wet areas near freshwater in northern Australia, on black, clay, or red loam soils.
- The species endures heat and dry seasons, using rhizomes to survive.

Heat and stress tolerance
- Tolerates high temperatures; at 45 C, shoot growth and leaf elongation remain robust and soluble sugars increase several-fold.
- This resilience is linked to thermally stable RuBisCO activase enzymes up to about 42 C.
- It also tolerates salinity and drought conditions.

Agricultural relevance
- O. australiensis carries genes that help resist diseases and pests (such as brown planthoppers) and is used in breeding programs to improve cultivated rice.

Genome
- It is the only known member of the EE genome clade, with an estimated genome size of about 965 million base pairs.
- Its large genome is largely due to many long terminal repeat retrotransposons (LTR-RTs), accounting for about 65% of the genome, with more than 90,000 LTR-RTs formed in the last few million years.

Endemism
- It is native to tropical northern Australia, alongside a few other wild Oryza species in the region.