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

CHAPTER 8
Nematodes
J-C. Prot and E.B. Gergon
Nematodes—unsegmented roundworms—feed
on microorganisms,
plants, or animals. They live in water
or in a film of water in the soil.
Plant parasitic nematodes are microscopic
and transparent. They live
in the rhizosphere, inside roots, or in
aerial plant tissues. They are disseminated
through irrigation and
flood water, wind, animals, human
activities, tools, and plant materials.
Plant parasitic nematodes feed and
reproduce on root and aerial plant
tissues. Nematodes damage the
plants by feeding and by producing
toxic metabolites or secretions.
Although more than 100 specics
of plant parasitic nematodes occur in
rice ecosystems, only a few have
been proven pathogenic to rice. The
pathogenic species of economic importance
are Aphelenchoides besseyi,
Criconemella onoensis, Ditylenchus
angustus, Heterodera spp.,
Hirschmanniella spp., Hoplolaimus
indicus, Meloidogyne spp.,
Paralongidorus australis, and
Pratylenchus spp. Only A. besseyi is
considered as it is the only nematode
known to be borne by rice seed, and
is, therefore, of quarantine importance.
8.1 Modified
Baermann funnel
and sieve methods.
Detection
Methods available for detecting A.
besseyi include the modified
Baermann funnel method, the sieve
method, and the manual dehulling
method. Nematodes may also be detected
during the washing test for
fungi.
For routine seed health testing
(RSHT), the modified Baermann funnel
or sieve method as described by
Gergon and Mew (1991) is less tedious
and more practical than the
manual dehulling method. Manual
dehulling should be employed for
quantitative analysis.
Nematodes may be detected from
seeds that have been used for RSHT
and from 100-500 seeds soaked in
water for 2 d.
Modified Baermann funnel method
(Fig. 8.1)
Procedure: 1. Place seeds over a 10-cm
diam, 40- × 40- mesh steel
wire dish fitted in a funnel
(12 cm diam) and filled with
250 ml tap water. Let the
setup stand for at least
48 h.
2.After incubation, draw approximately
20 ml of the
water into a test tube
through rubber tubing attached
to the funnel. Allow
the collected water to stand
for 1 h. Pipette out excess
water, leaving 10-15 ml in
the tube.
3. Examine water rernaining in
the tube for nematodes.
Count nematodes under a
stereobinocular microscope.