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

CHAPTER 11
Seed treatment
J.K. Misra. T.W. Mew, and C.C. Huelma
Seed treatment is physical or chemical
seed therapy. Seed treatment
dates back at least to the Roman empire,
when wine and crushed cypress
leaves were used to treat seeds
for better harvest.
Today, seed treatment is important
in pest management. In western
countries and Japan, where mechanized
farming is practiced, seed
treatment has become part of normal
farm procedures. Seed treatment
revolutionized production
(Nakamura 1986, Bowling 1986) by
controlling many pests and pathogens
and by repelling birds. As new
technologies and chemicals become
available, the dimensions of seed
treatment change significantly.
Seeds are treated
in the early stages of their germination
and establishment to protect
them from pests and pathogens,
to promote better seedling stands,
to minimize yield loss,
to maintain and improve seed
quality, and
to avoid introduction and spread
of harmful organisms.
Advantages of seed
treatment
Among the many advantages of seed
treatment are that it
protects seeds and seedlings from
pests and pathogens in the early
stages of germination and establishment,
is easier than plant treatment and
can be done indoors with or without
machinery,
is unaffected by weather conditions,
requires less chemicals than does
plant treatment,
pollutes the environment less than
does plant treatment,
does not result in much development
of resistance in insect pests (although
fungi are developing resistance
to fungicides), and
uses biocides that affect only targeted
organisms and not the other
beneficial entities in the soil.
Limitations of seed
treatment
Advantages of seed treatment outweigh
the limitations which include
lack of effective broad-spectrum
systemic fungicides for internally
seedborne fungi and for fungal resting
structures;
no protection beyond the early
growth or seedling stages;
no potent biocides that protect the
seeds from rodents, nematodes, insects,
slugs, and birds; and
chemicals do not continue to adhere
to the seed surface, do not
maintain the desired level during
germination, and do not protect germinating
seeds and seedlings from
seedborne and soilborne pests and
pathogens.
Methods
Seeds are treated by chemical, physical,
or both methods. Aspects of general
seed treatment are presented by
Jeffs (1986), Neergaard (1979), and
Anselme (1988). Information about
rice seed treatment for quarantine
purposes is presented here.
Physical seed treatment is any
method that does not employ chemicals.
Normally, heat treatment is accomplished
using hot water, dry
heat, or steam.
Heat treatment kills seedborne
pests and pathogens without injury
to most germplasm. Heat therapy
may be injurious to and should be
used cautiously with old or damaged
seeds and varieties which have
low heat tolerance. Japonica varieties
are generally more heat-sensitive
than indica varieties.
Hot water treatment at 52-57 °C
for 15 min eradicates seedborne
Aphelenchoides besseyi.
Heat therapy is often given in
conjunction with chemical treatment.
Biocidal chemicals (fungicides,
bactericides, insecticides,
nematicides) are applied as liquids
or powders. Depending on the type
of seed and the nature of the chemical,
biocides may be applied as dust
treatments, fumigants, wet treatments
(steep, sprinkle, quick wet,
and slurry), oil fungicide treatments,
and by pelleting. Since no broadspectrum
fungicide exists, mixtures
of fungicides are commonly used.
In Japan, the following chemicals
are used to control blast, bakanae,
and brown spot rice diseases
(Nakamura 1986):
thiram 20% and benomyl 20%
(benlate T);
thiram 30% and thiophanatemethyl
50% (Homai);
thiram 10% and thiophanatemethyl
10% (Homai coat);
captan 30% and kasugamycin 3%
(kasumin C); and
copper sulfate, basic 29%, and
oxine-copper 20% (oxybordeau).
Chemicals used for seed treatment
in the USA are
captan,
thiram,
maneb,
chloroneb,
difolatan ( cis --N-((l,l,2,2-
tetrachloroethyl) thio)4-
cyclohexene-1,2, dicarboximide),
Vitavax (2,3-dihydro-6-methyl-5-
phenyl carbamoyl-1,4-oxathiin),