Rice Origins: Asian and African Rice

• Rice is one of the oldest cultivated crops
• The somatic chromosome number is 2n=24

Cultivated Rice Species

• Asian rice: Oryza sativa
• African rice: O. glaberrima

Cultivated Asian Rice Races

• Indica
• Japonica (Sinica)
• Javanica

Origin Theories of Cultivated Rice

• Views on the origin of rice are grouped into polyphyletic and monophyletic origins.

Polyphyletic Origin

• Rice originated from several species.
• Asian rice (O. sativa) and African rice (O. glaberrima) evolved independently in their respective regions from several species.

Monophyletic Origin

• Both Asian and African rice arose from a common parent (O. perennis).
• This view is widely accepted because Asian and African rice are similar, apart from differences in glume pubescence, ligule size, and pericarp color, which is red in African rice.

Modern Perspectives on Rice Origin

• Most modern rice researchers believe in a monophyletic origin for cultivated rice.
• The Asian rice evolved from Oryza perennis in South East tropical Asia.
• African rice evolved in the upper valley of the Niger River in Africa.

Species in the Genus Oryza

• The genus Oryza includes 20 wild species.
• Two cultivated diploids: O. sativa and O. glaberrima.
• The remaining are wild species, including diploid and tetraploid forms.

Rice Breeding Objectives

• High yield potential
• Adaptability and stability of yield
• Early maturity
• Resistance to lodging and shattering
• Resistance to cold temperature
• Resistance to salinity and alkalinity
• Resistance to diseases and pests
• Improved grain quality

Improved Grain Quality Factors

• Grain shape and size
• Texture of endosperm and starch quality
• Aroma and cooking quality
• Kernel color
• Milling out turn

High Yield Potential Characteristics

• Short stature
• Thick, stiff culm
• Compact panicle
• Short, narrow, erect leaves for efficient solar radiation
• High tillering
• Non or low photo sensitivity
• Responsive to nitrogen
• Flag leaf angle not exceeding 40°

Adaptability and Stability of Yield

• Wide adaptability is important because rice is grown in diverse agroclimatic zones.
• Key characteristics: low sensitivity to temperature and light, and resistance to a wide range of pests and diseases.
• Consistency in yield across varying biotic and abiotic conditions is crucial.

Early Maturity

• Enables multiple cropping and helps avoid terminal drought and pests.
• Optimum early maturity is around 105 days; shorter durations may reduce yield.

Resistance to Lodging and Shattering

• Requires short stature, thick strong culm, short internodes, and tightly encircling leaf sheaths.
• Grain shattering is a complex trait also found in wild rices.

Resistance to Cold Temperature

• Important in regions like the Cumbum valley and Gudalur taluk of Nilgiris.
• Japonica rice varieties are generally more cold-tolerant.

Resistance to Salinity and Alkalinity

• Important in areas like Trichy and Dharmapuri districts of Tamil Nadu

Resistance to Diseases

-Important diseases include blast, Helminthosporium, bacterial leaf blight, and Tungro virus.

Resistance to Pests

• Important pests include brown plant hopper, stem borer, and rice gall midge.

Grain Shape, Size, and Texture

• Classified based on size, shape, and texture.
• Length categories: extra long (over 7 mm), long (6-7 mm), medium (5-5.99 mm), and short (below 5 mm).
• Shape is determined by the length/breadth ratio.

Grain Texture

• Hard starchy grains with translucent vitreous fracture.
• Soft dextrinous grains with opaque fracture, known as glutinous rice.

Aroma and Cooking Quality

• Some varieties have aroma when cooked due to chemicals like PANDAMARILACTIONE in the endosperm.
• Cooking quality varies with variety and grain type

Nutritive Value

• Protein content is about 8% in brown rice and 7% in polished rice and depends on environment and nitrogen application.
• Increasing protein may lower lysine content.

Kernel Color

• Preference varies by region; red rice is preferred in Kanyakumari and Kerala.

Milling Out Turn

• Unhusked rice is known as rough rice or paddy.
• Milling quality is determined by the head rice and total rice obtained.

Breeding for Alternate Dwarfing Genes

• Seeks to avoid reliance on the Dee-Gee-Woo-Gen dwarfing gene to prevent widespread vulnerability to pests or diseases

Breeding Varieties for Direct Sown Conditions

• Important due to water scarcity.
• Requires quick-growing varieties that suppress weed growth.

Varieties Suited for Dry Land Conditions

• Important in regions where rice is grown as a dryland crop.

Deep Water Paddy

• Needed in areas with deep water conditions.

Varieties Suited for Export

• Scented rice like Basmati 370, can be exported to Arab countries, but only Basmati rice from Himalayan valleys is preferred

Breeding Varieties to Control Wild Rice

• Necessitates marker genes in cultivated rice to distinguish them from wild rice.

Breeding Varieties to Suit Local Problems

• Involves identifying varieties for specific conditions, such as fitting a short-duration rice crop between two turmeric crops