Perennial wild red rice
[Oryza rufipogon Griff.][ORYSA][CDFA list: B][Federal Noxious
common wild rice, brownbeard rice, Oryza
aquatica Rosch., Oryza cubensis Eckman ex Gotoh &
Okura, Oryza fatua Koen. ex Trin., Oryza glumipatula
Steud., Oryza paraguayensis Wedd. ex E. Fourn, Oryza
perennis Moench., Oryza sativa L. ssp. rufipogon
(Griff). de Wet, Oryza sativa L. vars. abuensis
G.Watt, coarctata G.Watt, fatua Prain, paraguayensis
Franch. or Parodi, rubribarbis Desv., savannae
Korn., sundensis Korn., Oryza sativa L. forma spontanea
DESCRIPTION: Variable perennial wild rice of shallow
water, with floating or emergent leaves, to 4 m tall. Perennial
wild red rice is a serious weed of rice fields in many regions
of the world. Evidence suggests that cultivated rice (Oryza
sativa L.) was originally derived from perennial wild red
rice. Both species readily hybridize, and in Asia, hybridization
and backcrossing between perennial wild red rice and cultivated
rice has created a highly variable range of weedy perennial
wild red rice types, including annual types, resulting in
much taxonomic confusion. Annual types are often designated as
biotypes of Oryza rufipogon in the literature. However,
this distinction is controversial. The Federal and California
noxious weed ratings pertain only to perennial wild red rice.
Perennial wild red rice and hybrids have seed heads
that shatter (shed seed) before maturity. Otherwise
they are difficult to distinguish from commercial rice cultivars
with red grains. Red-coated grains from weedy plants cannot be
separated from commercial grains. After milling, white rice contaminated
with perennial wild red rice appears dirty or requires
additional milling, resulting in more broken grains and reducing
the value of the crop. perennial wild red rice is sometimes
used in rice breeding programs to impart certain characteristics
to rice cultivars. Native to Asia.
more vigorous than commercial rice, but usually difficult to distinguish.
Tufted to 20 cm in diameter, often with rhizomes. Lower
stems spongy, floating, rooting at the nodes. Blades 10-80 cm
long, 0.7-2.5 cm wide, often flat, glabrous, smooth to rough (scabrous),
typically not as long or erect as cultivated rice. Margins minutely
serrate. Sheaths open, often inflated in the lower portion. Ligules
membranous, triangular to narrowly triangular, 9-25(45)
mm long, usually split or ragged. Auricles lacking or 1-7 mm long,
narrow, curved, glabrous or lined with long hairs to 2 mm long.
and UNDERGROUND STRUCTURES: Roots fibrous, often with rhizomes.
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SPIKELETS/FLORETS: Panicles 12-30
cm long, 1-7 cm wide, with loosely ascending branches. Spikelets
early deciduous from above the vestigial glumes. Glumes reduced
to minute ridges on the stalk. Florets 3, the lower 2 sterile
and glume-like, the upper one fertile. Fertile floret +/- oblong,
7-11 mm long excluding lemma awn, ~ 2-3(4) mm wide. Lemma and
palea green to yellowish, often dark red at apex, covered with
stiff transparent hairs. Awn variable, stout, up to 11 cm long,
often reddish. Anthers 6, 3.5-6 mm long, yellow
or brown. Stigmas protruding, blackish-purple or brown. Grains
red-brown, 5-7 mm long, 1.4-2 mm in diameter.
CHARACTERISTICS: Leaves usually turn brown as grains mature.
HABITAT: Rice fields,
sites with shallow, standing or slow-running water.
DISTRIBUTION: At publication
time, no known populations of perennial wild red rice have
ever been found in California. Previous populations of perennial
wild red rice hybrids in the Sacramento Valley have been eradicated.
by seed and vegetatively from rhizomes. Seeds fall
near the parent plant or disperse to greater distances as rice
seed contaminants, with human activities, water, soil movement,
and possibly birds. Seeds do not survive ingestion by waterfowl.
Seeds are typically dormant at maturity. Dormancy is partly due
to the presence of inhibitors in the seed coat. Depending on the
biotype and environment, seed may remain dormant and viable for
up to 3 years or more under field conditions. Many seeds decay
during long periods of flooded conditions. Germination typically
occurs between 15-40º C (59-104º F). Seeds often germinate
slightly sooner and at lower temperatures than commercial rice
seeds. Some biotypes emerge from soil depths of up to 12 cm (~
FAVORING/DISCOURAGING SURVIVAL: Planting perennial wild red rice-free certified
seed may prevent new introductions of perennial wild red rice.
Continuous flooding reduces perennial wild red rice seed
survival and attracts ducks that feed on the grains.
Unlike perennial wild red rice, cultivated rice has persistent spikelets,
white or yellow anthers 0.8-2.5 mm long, and grains 2.2-4 mm in diameter.
Stigmas may be white, yellow, red, or blackish-purple.
Prevention and Control: This species is currently not known
to occur in California. Prevention of its introduction and establishment is
best achieved through using only certified seed. Additionally, any field equipment
being transported into California from other states where red rice is a problem
(i.e., Mississippi or Louisiana) should be thoroughly cleaned and inspected
for red rice seed before being brought into the state. The potential for introduction
and establishment may increase as the acreage of specialty market annual "red
rice" increases which is very similar to the true perennial red rice. The
perennial red rice may be discouraged by from establishing by spring tillage
and also appears to require permanent water which is not a typical practice
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