Rice

Oryza spp.

1. Identification and origin

Rice belongs to the genus Oryza (Poaceae family), with Oryza sativa L. (Asian) and Oryza glaberrima Steud. (African) being the most relevant cultivated species. O. sativa was probably domesticated about 8–10 thousand years ago in the humid regions of Asia (China and Southeast Asia), subsequently spreading to Europe, Africa and the Americas. It is currently one of the most important food crops in the world, forming the basis of the diet of more than half the global population.

2. Economic importance

Rice is one of the most produced and consumed cereals worldwide, with great economic and social relevance. In Portugal, production stands out in the regions of the Tagus Valley, Sado and Mondego. The grain is used for direct consumption, industrial processing (flours, beverages, extruded products) and animal feed. The crop has significant weight in international trade and is strategic for global food security.

3. Botanical characterisation

Annual herbaceous plant, with hollow culms and well-defined nodes. The leaves are linear, with a membranous ligule. The inflorescence is a compound panicle, where the spikelets that give rise to the grains develop. The root system is fasciculate and adapted to flooding conditions. The varieties are differentiated by habit, vegetative cycle, panicle architecture and grain characteristics (length, amylose content, colour).

4. Soil and climate requirements

Rice adapts to hot and humid climates, requiring average temperatures above 20 °C throughout the cycle. It is highly tolerant to waterlogging, being traditionally cultivated under a controlled flooding regime. It prefers clayey to clay-loam soils, with good water retention capacity. The ideal pH is between 5.5 and 7.0. Water availability is critical, especially during the panicle differentiation and grain filling phases.

5. Main pests

• Asian rice borer (Chilo suppressalis): perforations in the culms, causing lodging and reduced productivity.
• Stink bugs (Oebalus poecilus, O. insularis): sucking of the grains during formation, causing spots and loss of quality.
• Aphids (Aphididae): sap sucking and transmission of viral diseases.
• Rice flies (Hydrellia spp.): damage to seedlings and reduction of the stand.
• Mites (Tetranychidae): chlorosis and reduction of the photosynthetic area, especially under conditions of heat and dryness.

6. Main diseases

• Rice blast / Pyricularia disease (Magnaporthe oryzae): elliptical lesions on the leaves, necrosis on the culm and sterile panicles; it is the most destructive disease of the crop.
• Brown spot (Bipolaris oryzae): brown spots on the leaves and reduction of vigour.
• Stem rots (Fusarium spp., Sclerotium oryzae): structural weakening and lodging.
• Bacterial disease (Xanthomonas oryzae pv. oryzae): yellowish streaks that progress to necrosis.
• Viral diseases (Rice yellow mottle virus, Rice tungro virus – in tropical regions): chlorosis, dwarfism and strong reduction of production.

7. General crop management

It includes the use of certified seed, selection of varieties adapted to the region, adequate soil preparation and efficient water management (flooding, drainage and maintenance of the water level). Fertilisation should be balanced, avoiding excess nitrogen that favours the development of rice blast. Weed control is critical, especially in the early phases. Monitoring of pests and diseases should be continuous, complemented by practices such as crop rotation, straw management and strategic drainage. Harvesting should be carried out at the optimal point of ripening, minimising losses and ensuring grain quality.

Bibliographic references

• EPPO Global Database – Oryza sativa.
• CABI – Crop Factsheets – Rice (Oryza spp.).
• FAO – Rice Market Monitor and technical documents on rice production.
• IRRI (International Rice Research Institute). Rice Production Manual. Los Baños, Philippines.
• Smith, C. W., & Dilday, R. H. (Eds.). (2003). Rice: Origin, History, Technology, and Production. Wiley.