A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
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CHAPTER 12<br />
Weed <strong>seed</strong> contaminants<br />
K. Moody and R. Lubigan<br />
Most weed species have been, and<br />
still are, inadvertently disseminated<br />
between and within continents and<br />
countries as contaminants in traded<br />
<strong>seed</strong> (Horne 1953, Delouche 1988).<br />
Weeds <strong>of</strong> Philippine origin have<br />
been spread widely through export<br />
<strong>of</strong> high-yielding <strong>rice</strong> varieties.<br />
Weeds are also being disseminated<br />
in the continuing <strong>rice</strong> trade within<br />
South America; between South and<br />
North America; among Africa, North<br />
America, and Asia; and among most<br />
other combinations <strong>of</strong> trading partners<br />
(Delouche 1988). In California,<br />
with the exception <strong>of</strong> Echinochloa<br />
crus-galli (L.) P. Beauv. var crus-galli,<br />
all the introduced species <strong>of</strong> <strong>rice</strong><br />
weeds have been brought into the<br />
state in <strong>rice</strong> <strong>seed</strong> (Fuller and Barbe<br />
1983).<br />
<strong>Rice</strong> <strong>seed</strong> contaminated with<br />
weed <strong>seed</strong>s may introduce new species<br />
to a field or add to an existing<br />
weed population and is a source <strong>of</strong><br />
weed perpetuation in crop fields. In<br />
the southern USA, many weeds are<br />
spread almost entirely in <strong>rice</strong> <strong>seed</strong><br />
(Smith et al 1977).<br />
If there are 1,000 weed <strong>seed</strong>s per<br />
kilogram <strong>of</strong> <strong>rice</strong> <strong>seed</strong>, 100,000 weed<br />
<strong>seed</strong>s will be planted per hectare<br />
(10/m 2 ) if the <strong>seed</strong>ing rate is 100 kg/<br />
ha. Planting contaminated <strong>seed</strong> will<br />
be costly to a weed management<br />
program for many years (Rao and<br />
Moody 1990).<br />
In marketable <strong>rice</strong> grain, mixtures<br />
<strong>of</strong> weed <strong>seed</strong>s detract from its appearance<br />
and lower its grade and<br />
p<strong>rice</strong>. In Thailand, the p<strong>rice</strong> <strong>of</strong> <strong>rice</strong><br />
drops by about one-half when the<br />
grain is contaminated with weed<br />
<strong>seed</strong>s (Suwunnamek 1986).<br />
Standardized procedures are<br />
available for the types <strong>of</strong> inspection<br />
and <strong>testing</strong> needed to prevent weed<br />
<strong>seed</strong> contamination <strong>of</strong> crop <strong>seed</strong>. The<br />
12.1 Seeds <strong>of</strong><br />
Synedrella nodiflora<br />
(courtesy <strong>of</strong><br />
K. Moody and<br />
R. Lubigan).<br />
12.2 Seeds <strong>of</strong><br />
Cyperus compactus.<br />
12.3 Seeds <strong>of</strong><br />
Cyperus iria<br />
(courtesy <strong>of</strong><br />
K. Moody and<br />
R. Lubigan).<br />
12.4 Seeds <strong>of</strong><br />
Fimbristylis miliacea<br />
(courtesy <strong>of</strong><br />
K. Moody and<br />
R. Lubigan).<br />
12.5 Seeds <strong>of</strong><br />
Scirpus juncoides<br />
(courtesy <strong>of</strong><br />
K. Moody and<br />
R. Lubigan).<br />
12.6 Seeds <strong>of</strong><br />
Digitaria ciliaris<br />
(courtesy <strong>of</strong><br />
K. Moody and<br />
R. Lubigan).