Maclean et al. - 2002 - Rice almanac source book for the most important e

Transplanting is the planting of 1- to 6-wkold
seedlings in puddled soil with standing water.
Under these conditions, the rice plants have an
important head start over a wide range of competing
weeds, which leads to higher yields.
Transplanting, like puddling, provides farmers
with the ability to better accommodate the rice
crop to a finite and fickle water supply by shortening
the field duration (since seedlings are
grown separately and at higher density) and
adjusting the planting calendar.
With the development of puddling and transplanting,
rice became truly domesticated. In
China, the history of rice in river valleys and
low-lying areas is longer than its history as a
dryland crop. In Southeast Asia, however, rice
originally was produced under dryland
conditions in the uplands, and only recently
came to occupy the vast river deltas.
Migrant people from southern China or perhaps
northern Vietnam carried the traditions of
wetland rice cultivation to the Philippines during
the second millennium B.C., and Deutero-
Malays carried the practice to Indonesia about
1500 B.C. From China or Korea, the crop was
introduced to Japan no later than 100 B.C.
Movement to western India and south to Sri
Lanka was also accomplished very early. Rice
was a major crop in Sri Lanka as early as 1000
B.C. The crop may well have been introduced to
Greece and the neighboring areas of the
Mediterranean by returning members of
Alexander the Great’s expedition to India around
344-324 B.C. From a center in Greece and Sicily,
rice spread gradually throughout southern
Europe and to a few locations in northern Africa.
Rice in the New World
As a result of Europe’s great Age of Exploration,
new lands to the west became available for exploitation.
Rice cultivation was introduced to the
New World by early European settlers. The Portuguese
carried it to Brazil and the Spanish introduced
its cultivation to several locations in Central
and South America. The first record for
North America dates from 1685, when the crop
was produced on the coastal lowlands and
islands of what is now South Carolina. The crop
may well have been carried to that area by slaves
brought from the African continent. Early in the
18th century, rice spread to what is now
Louisiana, but not until the 20th century was it
produced in California’s Sacramento Valley. The
introduction into California corresponded almost
exactly with the timing of the first successful
crop in Australia’s New South Wales.
Genetic diversity
Two rice species are important cereals for human
nutrition: Oryza sativa, grown worldwide, and O.
glaberrima, grown in parts of West Africa. These
two cultigens—species known only by cultivated
plants—belong to a genus that includes about 20
other species.
Wild Oryza species are distributed throughout
the tropics. They can be grouped into four
complexes of closely related species (Table 1).
Two species, however, seem to be different from
others in the genus: the tetraploid O. schlechteri
and the diploid O. brachyantha.
Species of the O. ridleyi complex inhabit
lowland swamp forests and species of the O.
meyeriana complex are found in upland hillside
forests.
The O. officinalis complex consists of
diploid and tetraploid species found throughout
the tropics. All the species in this complex are
perennial; some are rhizomatous and others form
runners. They also differ in the habitats where
they are found. Some occur in full sun, others in
partial shade. Variation exists within these species
as shown by the responses of different
populations to pests and diseases.
The O. sativa complex consists of the wild
and weedy relatives of the two rice cultigens as
well as the cultigens themselves. The wild
relatives of O. glaberrima in Africa consist of the
perennial rhizomatous species O. longistaminata,
which grows throughout Sub-Saharan Africa, and
Madagascar, and the annual O. barthii, which
extends from West Africa to East and Southern
Central Africa. The annual and weedy relatives
of O. glaberrima are found primarily in West
Africa.
Among the wild relatives of O. sativa, the
perennial O. rufipogon is widely distributed over
South and Southeast Asia, southeast China, and
Oceania; morphologically indistinguishable
forms are found in South America, usually in
deepwater swamps. A closely related annual wild
form, O. nivara, is found in the Deccan Plateau
and Indo-Gangetic Plain of India and in many
parts of Southeast Asia. The habitats of O. nivara
are ditches, water holes, and edges of ponds.
Morphologically similar to (and sometimes in-
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