A manual of rice seed health testing - IRRI books - International Rice ...

CHAPTER 5
Dry seed inspection
J.K. Misra, C.C. Huelma, and T.W. Mew
Dry seed inspection detects smut
balls (false smut); smutted seeds
(kernel smut); diseased, discolored,
or deformed seeds; germinated
seeds; insect-damaged seeds; seeds
of rice varieties other than that specified;
weed seed contaminants; insects;
mites; other plant parts; and
inert materials such as soil.
The whole submitted sample
should be visually inspected with or
without a stereobinocular microscope
or a magnifying lens (Fig. 3.2,
3.3).
Weeds
Most weed species have been, and
still are, inadvertently disseminated
between and within continents and
countries as contaminants in traded
seed (Horne 1953, Delouche 1988).
Weeds of Philippine origin have
been spread widely through exportation
of seed of high-yielding rice varieties.
In California, all the introduced
species of rice weeds (except
Echinochloa crus-galli (L.) P. Beauv.
var. crus-galli ) were brought into the
state in rice seed (Fuller and Barbe
1983).
Weeds that mature at the same
time as rice are harvested and
threshed with the rice. Rice seed that
is contaminated with weed seeds
may introduce new species to a field
or add to an existing weed population
and is a source of weed perpetuation.
In the southern United States,
many weeds are spread almost entirely
in rice seed (Smith et al 1977).
Once planted, contaminated seed
can result in weed management
problems for many years (Rao and
Moody 1990).
Admixture of weed seeds in marketable
grain detracts from its quality
and appearance, thereby lowering
its grade and price. In Thailand,
the price of rice drops by about onehalf
when the grain is contaminated
with weed seeds (Suwunnamek
1986).
Important weed pests are listed in
Chapter 12.
Insects
Insects are among the most important
pests affecting seed health in the
field, in transit, or in storage. Many
stored grain pests are distributed
worldwide.
Insect pests spread mainly
through trade between countries and
continents. They may be transported
in packaging, cabins, etc. The maize
weevil, lesser grain borer, Indian
meal moth, flour moth, and other
pests entered the USSR from the
USA with imported maize stalks,
French beans, and cacao beans from
1921 to 1923. Some insects acclimatized
and spread further. The rice
stem borer was introduced to Iran in
1977 with rice-straw wrapping on
citrus cuttings imported from Japan
(M.D. Pathak, 1988, pers. commun.).
"Some dangerous pests of stored
grains like the khapra beetle, broadnosed
grain weevil, cowpea beetle,
and flour-spotted bean weevil... were
introduced into the USSR several
times with imported cereals and legumes,
but they were localized at insignificant
points, thanks to timely
quarantine measures" (Zakladnoi
and Ratanova 1987).
Although not all newly introduced
pests have damaged their
new environments, some have
wreaked great havoc.
Important insect pests are listed in
Chapter 13.