|Rice Root Nematode||Classification||Hosts|
|Morphology and Anatomy||Life Cycle|
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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 with mixtures.
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.
A-rated pests in California.
Migratory endoparasite of roots. Juveniles and adults enter behind the root tip and move in air channels; can also migrate into older roots.
Nematodes do not migrate up into stem.
Rice, corn, sugarcane, grasses, and sedges.
For an extensive list of host plant species and their susceptibility, copy the name
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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 invasion.
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 called "Mentek."
Host Plant Resistance
There is no significant resistance in rice varieties to H. oryzae, although there is considerable tolerance due to repeated individual selection.
For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name
select Nemabase Resistance Search and paste the name in the Genus and species box
Fumigant nematicides are effective in dry fields, but economically questionable.
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.