Rice

Kingdom: Plantae

Order: Poales

Family: Poaceae

Genus: Oryza

Species: O. sativa

ABOUT RICE

Oryza Sativa, it is believed, is associated with wet, humid climate, though it is not a tropical plant. It is probably a descendent of wild grass that was most likely cultivated in the foothills of the far Eastern Himalayas. Another school of thought believes that the rice plant may have originated in southern India, then spread to the north of the country and then onwards to China. It then arrived in Korea, the Philippines (about 2000 B. C.) and then Japan and Indonesia (about 1000 B. C.).

The journey of rice around the world has been slow, but once it took root it stayed and became a major agriculture and economic product for the people. In the Indian subcontinent more than a quarter of the cultivated land is given to rice (20011-12). It is a very essential part of the daily meal in the southern and eastern parts of India. In the northern and central parts of the subcontinent, where wheat is frequently eaten, rice holds its own and is cooked daily as well as on festivals and special occasions.

India is an important centre of rice cultivation. The rice is cultivated on the largest areas in India. Historians believe that while the indica variety of rice was first domesticated in the area covering the foothills of the Eastern Himalayas (i.e. north-eastern India), stretching through Burma, Thailand, Laos, Vietnam and Southern China, the japonica variety was domesticated from wild rice in southern China which was introduced to India. Perennial wild rice still grow in Assam and Nepal. It seems to have appeared around 1400 BC in southern India after its domestication in the northern plains. It then spread to all the fertile alluvial plains watered by rivers. Some says that the word rice is derived from the Tamil word arisi.

GROWTH STAGES OF RICE

CLIMATE REQUIREMENT

In India, rice is grown under widely varying conditions of altitude and climate. Rice cultivation in India extends from 8 to 350N altitude and from sea level to as high as 3000 meters. Rice crop needs a hot and humid climate. It is best suited o regions which have high humidity, prolonged sunshine and an assured supply of water. The average temperature required through out the life period of the crop ranges from 21 to 370C. at the time of tillering the crop requires a higher temperature than for growth. Temperature require for blooming is in the range of 26.5 to 29.50C. at the time of ripening the temperature should be between 20-250C. photoperiodically, rice is a short-day plant. However, there are varieties which are non-sensitive to photoperiodic conditions.

The regions cultivating this crop in India are distinguished as the western coastal strip, the eastern coastal strip, covering all the primary deltas, Assam plains and surrounding low hills, foothills and Terai region- along the Himalayas and states like West Bengal, Bihar, eastern Uttar Pradesh, eastern Madhya Pradesh, northern Andhra Pradesh and Odisha. India, being a land of the eternal growing season, and the deltas of the Ganges-Bramhaputra(in West Bengal), Kaveri River, Krishna River, Godavari River, Indravati River and Mahanadi River with a thick set-up of canal irrigation like Hirakud Dam and Indravati Dam, permits farmers to raise two, and in some pockets, even three crops a year. Irrigation has made even three crops a year possible.

SOIL

Soils with good water retention capacity with high amount of clay and organic matter are ideal for rice cultivation. Clay or clay loams are most suited for rice cultivation. Such soils are capable of holding water for long and sustain crop. Rice being a semi-aquatic crop, grows best under sub-merge conditions. Rice is cultivated in almost all types of soils with varying productivity. The major soil groups where rice is grown are riverine alluvium, red-yellow, red loamy, hill and sub-montane, Terai, laterite, costal alluvium, red sandy, mixed red, black, medium and shallow black soils. It grows well in soils having a pH range between 5.5 and 6.5.

RICE BLAST

Disease Symptoms:

The rice blast fungus may infect and produce lesions on most of the shoot but usually not the leaf sheath. From the seedling stage through plant maturity, rice blast progresses through several phases starting with leaf blast, followed by collar, panicle and node blast. Leaf Symptoms

BACTERIAL BLIGHT

Disease Symptoms:

Bacterial blight is caused by Xanthomonas oryzaepv. oryzae (Xoo) and affects the rice plant at the seedling stage where infected leaves turn grayish green and roll up. As the disease progresses, leaves turn yellow to straw-colored and wilt, leading whole seedlings to dry up and die.

SHEATH BLIGHT

Disease Symptoms:

The fungus affects the crop from tillering to heading stage. Initial symptoms are noticed on leaf sheaths near water level. On the leaf sheath oval or elliptical or irregular greenish grey spots are formed. As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border.