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Nematode around 2 mm long.
overlap of esophagus over intestine.
Diovarial females, sexually reproducing.
Typical pratylenchid stylet.
Nematodes are unusually long for endoparasites, but
inhabit air channels rather than an intracellular environment.
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
Hirschmanniella oryzae is found throughout rice-growing regions, Asia, Japan,
West Africa, South America, U.S. in Texas and Louisiana; thought not to be
present in California. Sher
found complexes of several species in collections from rice, including H. spinicaudata
and H. belli. Literature prior to 1968 may deal
Zheng surveyed 100 rice fields around Northern California and
concluded all populations were H. belli.
Much lower populations of H. belli were observed in California than
with H. oryzae in China.
Nematode is commonly associated with sedges between crops,
especially in wet ditches, and with common cattail (Typha latifolia) along streams and ditches.
in California Nematode Pest Rating System.
endoparasite of roots. Juveniles and adults
enter behind the root tip and move in air channels; can also migrate into older
Nematodes do not migrate up into stem.
Rice, corn, sugarcane, grasses, and sedges.
Eggs hatch occurs in 4-5 days in roots; and development to adult
takes about 1 month.
Two or more generations are produced per growing
season, with a 10- to 15-fold increase - up to 250/g root.
Nematodes are more common in damp paddy fields than drained and
dried fields. It survives poorly in dry fields.
Nematode can survive without food
for several weeks; may overwinter in dead roots as eggs (if kept moist), also as
juveniles and adults.
There is a positive correlation between population densities and pH.
Weeds in and around rice paddies are important survival hosts.
Infestation retards growth, decreases height, delays tillering, and reduces
weight of dry matter.
Causes necrosis of penetrated epidermal cells, damage and destruction of
cortical cells resulting in cavities in cortex, necrotic regions, and secondary
This nematode occurs with H. spinicaudata in West Africa and the
combination reduces rice yields by 20%. In contrast to H. oryzae. H.
spinicaudata survives well in dry soils.
Previously, H. oryzae was thought to cause a serious disease of rice
There is no significant resistance
in rice varieties to H. oryzae, although there is considerable tolerance
due to repeated individual selection.
Host Plant Resistance, Non-hosts and Crop Rotation alternatives:
Fumigant nematicides are effective in dry fields, but economically
In trials conducted by A.L. Taylor in Thailand, treatment of soil in
rice seedbeds with nematicides (1,3-Dichloropropene
(Telone) (then D-D mixture), DBCP, or methyl bromide) and treatment of paddy
soil with either D-D or DBCP (both by injection and then flooding) or by
flooding and then mixing in DBCP or D-D, increased rough rice yields by 24 to
37%. The weight of plants increased by as much as 95% and tillering
increased as much as 43%.
Rotation to non-hosts for 1 year is effective, but may be impractical.
A prolonged dry period between crops is effective, but may also be
difficult to achieve.
Heavy fertilization has been recommended to help offset reduced yields.
In West Africa, H. spinicaudata can
reduce rice yields by 20%, and can survive the dry season well in root debris;
however, if the fields are flooded between crops, causing the roots to decay,
hydrogen sulfide is released and H. spinicaudata survives poorly
(research by Fortuner in Senegal). But flooding
may be difficult to achieve as river flow diminishes during the dry season,
making water less available.