world. In North America and other countries: very early maturing (96–117 days);
In India: very early (less than 110 days); early (110–140 days); late (150–170 days);
very late (180 days +). Some varieties only mature in 260 days.
- ssp. indica—Tropical Rice, mainly grown between latitude 0
- ssp. javanica—Javanese Rice, mainly in equatorial regions. Low yield potential.
Varieties of Rice
Many thousands of varieties of rice are available—more than 5000 in India alone.
As rice is mainly self-pollinated, farmers can save their own seed from year to year
and so build up their own composite variety (discussed in 1Fd, page 53) that is
adapted to their area. Mixtures of varieties are also commonly grown together.
Varieties often display different characteristics when grown in different
environments.
The International Rice Research Institute (IRRI), is based in the Philippines and
has had great success in breeding improved rice varieties, particularly hybrids.
Varieties developed and released by IRRI are prefixed with “IR” eg IR8, IR20, etc.
Development of perennial rice strains has not yet proved very successful.
Hybrid rice has been growing in popularity since the 1970s; in China in 1992-93
for example, 19 million hectares of hybrid rice was planted, around 65% of the
country’s rice area. Under irrigation, hybrids generally yield about one MT per
hectare more than the semi-dwarf modern “conventional” varieties. Future hybrid
rice seed could be based on apomixis (discussed in pages 2 and 3)—apomixis is
asexual reproduction whereby farmers could retain apomictic hybrid seed from their
own crops for many seasons.
PLANTING
Propagation: by seed. Although often planted first in nurseries and transplanted at
4–6 weeks, there is often no yield advantage to this system though there are other
advantages. The seed can be planted directly into dry soil, and the field then
submerged; or it can be broadcast into a water-submerged field; or sown into a wet
field, in which case the seed is often pre-germinated ie soaked in water for 24–36
hours, then kept in the dark for a further 24–36 hours.
Germination: most indica varieties have a 1–3 month dormancy. Japonica varieties
and others that are insensitive to photoperiod (1Ej) have no dormancy period. The
early maturing (117–132 days); mid-season (132–150 days); late (150–180 days).
°°
129
- Growth Period. There are two main classifications, used in different parts of the
There are 3 sub-species of Oryza sativa:
and 25 in the tropi-
cal monsoon zones. 1–3 month seed dormancy. Tall, leafy, many tillers, susceptible
to lodging, low response to fertiliser, more hardy and resistant to diseases and
and poor growing conditions, photoperiod sensitive.
- ssp. japonica—Temperate or Pearl Rice, mainly grown in temperate regions. Short,
stiff straw and therefore resistant to lodging, fewer leaves or tillers, early maturing,
It is grown mainly in Japan, South Korea, North China, New South Wales, South
Europe, California and South America.