Principles of Plant Genetics and Breeding

A British sea captain brought rice to the US from
Madagascar. The first commercial planting occurred in
South Carolina in about 1685. Early rice production
concentrated in the southeast US where South Carolina,
Georgia, Louisiana, North Carolina, Mississippi, Alabama,
Kentucky, and Tennessee were major producers in the
early 1800s. However, in the early 19th century, shifts
in rice production started in the US, reaching its highest
in the late 1900s. Production became more modernized
and spread to Arkansas and the Mississippi River delta
where the flatter lands permitted larger scale, high-tech
production (mechanized, irrigated, etc.). In 1838,
South Carolina produced about 75% of the US total rice
crop. In 1903, Louisiana and Texas produced 99% of
the US crop. However, by 1990, Arkansas, Louisiana,
and Mississippi accounted for more than two-thirds of
the US rice production, with Texas and California
accounting for most of the balance. Rice production
in the USA is currently concentrated in the Arkansas
grand prairie, the Mississippi River delta, southwestern
Louisiana, the coast prairie of Texas, and the Sacramento
Valley of California.
Adaptation
Rice may be described as a semiacquatic plant. Rice is
adapted to very wide agroecological zones, ranging
from dry to submerged root growing conditions. Four
general ecosystems can be identified for commercial rice
production around the world, based on elevation, rainfall
pattern, depth of flooding, and drainage.
Rainfed lowland rice ecosystems
This ecosystem is common in densely populated rural
regions of the world, where producers face severe economic
challenges in addition to burgeoning population.
Rice production under these conditions account for
about 25% of the world’s harvested rice area and 17% of
the world’s production. Producers prepare the land by
puddling the soil or dyking fields to hold water for a
variable duration of flooding, according to the rainfall.
The soils alternate between flooded to dry conditions
during the growing season. Rice is direct-seeded or
transplanted into the field.
Upland rice ecosystems
Upland rice production occurs on well-drained, level
to steeply sloping farmlands. These soils are frequently
BREEDING RICE 499
moisture deficient. Upland production occurs in regions
of the world where slash-and-burn agriculture is common.
The removal of vegetation from these slopes predisposes
the soil to physical deterioration and nutrient
depletion. Crop yields are generally low. Upland rice
production constitutes about 13% of the world’s harvested
area and only 4% of the total rice produced. Rice
is direct-seeded to non-flooded soils.
Flood-prone rice ecosystems
Rice production in certain areas occurs on flooded
soils throughout the growing season, until harvest time.
Rice is direct-seeded or transplanted into flooded fields
(50–300 cm deep in water) during the rainy season.
Flooded rice production occurs widely in South and
South East Asia, and some parts of West Africa and Latin
America. Problems of salinity and toxicity from various
ions are common in this ecosystem. Crop yields are
unpredictable and generally low.
Irrigated rice ecosystems
The key feature of this system is that moisture is controlled
in both the dry and wet seasons. Various methods
are used to provide and regulate soil moisture. About
55% of the world’s harvested area and 75% of total
production occurs in irrigated ecosystem. Production
involves the use of modern technology with high production
inputs (e.g., fertilizers). Consequently, yields
are high, reaching about 5 t/ha in the wet season to
about 10 t/ha in the dry season.
Other classifications
T. Chang of the International Rice Research Institute
(IRRI) reported a classification of rice according to
topohydrological, edaphic, cultural, and seasonal criteria.
According to ecogoegraphic differentiation, rice may be
classified into three races of O. sativa as indica, javanica,
and sinica (or japonica). The japonica race has upland
and lowland cultivars, whereas the indica has cultivars
that span dryland to deep water and floating cultivars.
Commercial classes
Rice varieties are primarily classified according to
the length of the grain – short (5.5 mm), medium
(6.6 mm), and long (7–8 mm). The shorter grained
varieties are also called japonica types, and have short,