Preferred name: Hirschmanniella oryzae
Authority: (van Breda de Haan) Luc & Goodey
Taxonomic position: Animalia: Nematoda: Chromadorea: Rhabditida: Pratylenchidae
Other scientific names: Anguillulina oryzae (van Breda de Haan) Goodey, Hirschmannia oryzae (van Breda de Haan) Luc & Goodey, Hirschmanniella abnormalis Renubala, Dhanachand & Gambhir, Hirschmanniella apapillata (Imamura) Siddiqi, Hirschmanniella exacta Kakar, Siddiqi & Khan, Hirschmanniella exigua Khan, Hirschmanniella nana Siddiqi, Radopholus oryzae (van Breda de Haan) Thorne, Tylenchus oryzae van Breda de Haan
Common names in English: rice root nematode
view more common names online...
Notes on taxonomy and nomenclature EPPO Code: HIRSOR

Rice (Oryza sativa) is the major host of the rice root nematode Hirschmanniella oryzae. Damage to rice caused by H. oryzae is widely reported (Cuc & Prot, 1992; Peng et al., 2018); however, population levels of the nematode vary depending on rice varieties (Maung et al., 2010; Anwar et al., 2011).

Several authors (Ibrahim et al., 2010; Anwar et al., 2011; Abd-Elbary et al., 2012) have reported that weeds growing in and around rice fields are hosts of H. oryzae. Plants in the families of Cyperaceae, Poaceae, Sphenocleaceae are classified as good hosts (Ibrahim et al., 2010; Anwar et al., 2011; Abd-Elbary et al., 2012; Maung et al., 2013).

There are diverging reports in the literature regarding the association of H. oryzae with cultivated crops other than rice. Babatola (1979) and Prasad et al. (1987), citing other authors, refer to findings of H. oryzae in association with cotton (Gossypium hirsutum), sugarcane (Saccharum officinarum), wheat (Triticum aestivum) and pearl millet (Cenchrus americanus). Other authors have reported that H. oryzae does not infect or multiply in the roots of cotton, maize and wheat (Mathur & Prasad, 1973; Youssef & Eissa, 2014). In Egypt, although low population levels of H. oryzae could be found in soil from wheat crops (Eissa et al., 2013; Korayem et al., 2019), no H. oryzae was extracted from wheat roots (Eissa et al., 2013). In experiments, wheat, cotton, sugarcane, pearl millet, maize (Zea mays), okra (Abelmoschus esculentus) and tomato (Solanum lycopersicum) were documented as susceptible to H. oryzae (Babatola, 1979; Prasad et al., 1987). However, for cotton, wheat and maize and other crops, Abd-Elbary et al. (2012) and Mathur & Prasad (1973) do not support these findings since the nematode failed to penetrate and/or multiply inside roots of tested crops. Finally, H. oryzae was found associated with rhizomes of the aquatic ornamental plant Cryptocoryne spp. (Araceae) imported into Europe (EPPO, 1976), though no further information was documented afterwards.

Host list: Amaranthus caudatus, Bolboschoenus maritimus, Chenopodiastrum murale, Chenopodium album, Cryptocoryne, Cyperus compressus, Cyperus difformis, Cyperus elatus, Cyperus haspan, Cyperus iria, Cyperus pilosus, Cyperus platystylis, Cyperus procerus, Cyperus pulcherrimus, Cyperus rotundus, Cyperus sanguinolentus, Echinochloa colonum, Echinochloa crus-galli, Echinochloa glabrescens, Eleocharis spiralis, Eleusine indica, Fimbristylis ferruginea, Fimbristylis globulosa, Fimbristylis quinquangularis subsp. quinquangularis, Hydrolea zeylanica, Kyllinga brevifolia, Lepidium didymum, Leptochloa chinensis, Marsilea crenata, Marsilea minuta, Oryza sativa, Paspalum distichum, Paspalum scrobiculatum, Pontederia vaginalis, Rotala rosea, Rumex dentatus, Schoenoplectiella supina, Sphenoclea zeylanica

H. oryzae is widely distributed in major rice growing areas of the world and commonly found in tropical and subtropical regions. According to Singh et al. (2022), H. oryzae is present in different regions and countries in Asia, the Asia-Pacific region, South America, Central America, Africa and the United States (Arkansas, Florida, Louisiana and Texas).

Africa: Burkina Faso, Cote d'Ivoire, Egypt, Gambia, Ghana, Guinea, Madagascar, Mali, Mauritania, Niger, Nigeria, Senegal, Sierra Leone
Asia: Bangladesh, Cambodia, China (Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hebei, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Sichuan, Xianggang (Hong Kong), Yunnan, Zhejiang), India (Andhra Pradesh, Assam, Bihar, Chhattisgarh, Goa, Gujarat, Haryana, Himachal Pradesh, Jammu & Kashmir, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Odisha, Punjab, Rajasthan, Tamil Nadu, Tripura, Uttarakhand, Uttar Pradesh, West Bengal), Indonesia (Java, Kalimantan), Iran, Japan (Honshu, Kyushu), Korea, Republic, Malaysia (West), Myanmar, Nepal, Pakistan, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, Vietnam
North America: United States of America (Arkansas, Florida, Louisiana, Texas)
Central America and Caribbean: Costa Rica, El Salvador
South America: Argentina, Brazil (Piaui), Ecuador, Guyana, Venezuela

H. oryzae is a migratory endoparasitic nematode. All life stages are infective except eggs. Nematodes enter the young roots through the epidermis at some distance from the tip, feeding intracellularly in parenchyma cells of the cortex and migrate within the root (Keoboonrueng, 1971; Babatola & Bridge, 1980). Males are needed for reproduction, oviposition occurs some days after females have penetrated the roots (Fortuner & Merny, 1979; Karakas, 2004). Juveniles hatch 4-6 days after egg deposition and the life cycle is completed in about a month under favourable conditions (28 ± 2°C and 87% - 90% relative humidity) (Siddiqi, 1973; Karakas, 2004). In Myanmar the multiplication factor in roots ranged 1.1 to 7.2 depending on the rice variety (Maung, 2011), while according to Siddiqui (1973) it can be as high as 13 per generation. However, there is no correlation between the initial population and the multiplication factor (Maung, 2011; Abd-Elbary et al., 2012). The maximum root population occurs between the tillering and the heading stage of rice crops, decreases afterwards and is lowest at harvest (Fortuner & Merny, 1979; Maung et al., 2013; Peng et al., 2018). The population pattern in soil is similar to that in the roots during the growing season (Maung et al., 2013). The number of generations of H. oryzae per growing season varies in different areas, for example one generation is reported per growing season in India, two in Japan and three in Senegal (Fortuner & Merny, 1979; Peng et al., 2018). The nematode can be found in different rice ecosystems but mainly in irrigated and lowland rice. H. oryzae can survive longer in roots than in soil, but under flooded conditions nematodes survival inside the root is shorter due to the faster decay of roots (Fortuner & Merny, 1979; Peng et al., 2018). H. oryzae can survive in weeds and rice stubble left in the field between crops (Mathur & Prasad, 1973; Peng et al., 2018). Soil temperature ranging from 21 to 28°C is optimal for multiplication. Maung et al. (2013) observed that H. oryzae can survive in fields with average soil temperatures between 20°C and 34°C. In the absence of a host, H. oryzae can survive in the soil for at least 5 months and, by means of a quiescence stage, nematodes can survive up to 12 months in soil that is not continually wet. H. oryzae can survive a wide range of pHs and adapts better to clay soils than to sandy soils (Mathur & Prasad, 1973; Fortuner & Merny, 1979; Babatola, 1981; Peng et al., 2018). The pest survives under anaerobic conditions which are suitable for rice production (Babatola, 1981).

Symptoms

Symptoms induced by H. oryzae are not specific, and are therefore not easily identifiable and usually unrecognizable in the field. In general, the infected rice seedlings show some chlorosis, retardation of growth, reduced and delayed tillering, and delayed flowering by 15-21 days (Keoboonrueng, 1971; Babatola & Bridge, 1979; Babatola & Bridge, 1980; Siddiqi, 1973; Goswami et al., 2015; Peng et al., 2018). Thirty to forty five days after transplanting of rice seedlings, infected rice roots may show yellowish to brown lesions that eventually darken. Heavily infected roots may decay after turning brown or black if the root system is heavily infected (Goswami et al., 2015; Peng et al., 2018). The browning of roots caused by H. oryzae may be enhanced by soil micro-organisms (Lee & Park, 1975).

Morphology

Morphological characters of H. oryzae are mentioned in Siddiqi (1973). The nematode is long and slender, and there is no sexual dimorphism in the head region between females and males. The lip region is not hemispherical. The stylet is strong with round basal knobs. The tail terminus is pointed or round with a sharp mucron.

The female body is straight or slightly arcuate ventrally. The median oesophageal bulb is oval and well developed. Oesophageal glands are elongate and ventral overlapping the intestine. The secretory excretory (SE) pore is anterior to the pharyngeal-intestinal valve. The female genital system is prominent, vulva median with two functional and equally developed genital tracts. The spermatheca is oval or sometimes round, containing sperm. ‘Thorneian cells’ appear to be of hypodermal origin and serve to connect the intestinal epithelial cells with the hypodermis, sometimes showing up to 3 nerve-like branches. The intestine does not overlap the rectum. The tail is elongate-conoid, and in length measures 4.3-5.5 times the body width at the anus.

Bursa is present in the males, arising near the head of spicule and ending near phasmids. The spicule is distinctly cephalated, slightly arcuate but not reaching the tail tip, the gubernaculum is simple and not-protruding.

Measurements are provided in Khun et al. (2015).

Detection and inspection methods

The EPPO diagnostic protocol PM 7/94 (2) Hirschmanniella spp. (EPPO, 2022) provides information for the detection and identification of nematodes belonging to the genus Hirschmanniella.

Hirschmanniella nematodes can be detected by extraction from soil and roots (EPPO, 2022). Extraction methods are given in EPPO Standard PM 7/119 (1) (EPPO, 2013). Both root and rhizosphere soil samples should be taken to detect the presence and to provide a more reliable estimate of H. oryzae numbers. Cutting roots into small pieces or macerating them in a blender before extraction can improve the detection efficacy.

The EPPO diagnostic protocol (EPPO, 2022) provides dichotomous keys to Pratylenchidae genera, as well as a key to Hirschmanniella species (based on Khun et al., 2015). Using morphological and morphometrical characters is the common technique to identify Hirschmanniella to genus and species level (Ahmad & Jairajpuri, 1976; Siddiqi, 2000, EPPO, 2022). However, because of the potential presence of closely-related Hirschmanniella spp. in the same fields (Babatola, 1984: Ichinohe, 1988), and sometimes intraspecific morphological and morphometric divergences within the same species (Khun et al., 2015; Mwamula et al., 2022), species level identification by morphology and morphometrics alone is complicated. Molecular tests for the identification of the genus Hirschmanniella are not yet available (EPPO, 2022). Khun et al. (2015) suggested using molecular tests to confirm species level identification. Few reports exist so far of molecular research on H. oryzae to identify the nematode, to distinguish morphologically closely-related species, and to re-evaluate the characters of species that have been already reported (Katsuta et al., 2016; Khun et al., 2015; Indarti et al., 2020; Mwamula et al., 2022; Alma et al., 2023). The DNA barcoding protocols for nematodes in EPPO Standard PM 7/129 (EPPO, 2021) have not been validated for Hirschmanniella spp. including H. oryzae (EPPO, 2022).

H. oryzae is normally spread by rice plants, especially seedlings from nurseries to the field and widely spread where there is long history of rice cultivation (Peng et al., 2018). Direct seeding of rice rather than transplanting, whenever possible, prevents the spread of H. oryzae from infested nurseries to the fields. Dispersal over longer distances is possible by irrigation water, plants for planting (including aquatic plants according to Jeger et al. (2018) in relation to Hirschmanniella spp.), soil associated with plants for planting, agricultural machinery, tools and field workers (Siddiqi, 1973). In international trade, infested plants for planting (except seeds) of rice and infested growing medium are the main pathway of H. oryzae. Plants for planting of other hosts (including weeds), their underground plant parts and associated growing medium may also be a pathway for the nematode.

Economic impact

It is difficult to determine yield losses under field conditions as they depend upon several factors such as rice varieties, nematode population density in relation to crop growth stage, cultural practices and soil conditions (Ichinohe, 1988; Maung, 2011). In Japan, no clear data was obtained on the actual yield reduction caused by H. oryzae (Ichinohe, 1988). Nevertheless, there have been reports of 24-56% yield reduction caused by H. oryzae (MacGowan, 1979; Youssef & Eissa, 2014; Peng et al., 2018). Different inoculation experiments showed varying degrees of yield losses, depending on rice varieties, inoculum density and soil fertility (Babatola & Bridge, 1979; Fortuner & Merny, 1979; MacGowan, 1979; Prasad et al., 1987; Maung, 2011; Youssef & Eissa, 2014; Peng et al., 2018). In fields that are not well fertilized, economic damage is expected when 800 H. oryzae are present in the roots of a single plant at the heading stage, which may correspond to as few as 40 H. oryzae in a plant one week after transplanting (Khuong, 1987). In Egypt, Youssef & Eissa (2014) reported that the presence of 1000 H. oryzae per 2 kg soil is a critical population density where damage was observed.

Control

The recommended management practices for H. oryzae include:

Chemical treatments such as soaking of the seeds, bare root dips before transplanting in nurseries, soil incorporation, application in standing water and ‘mud ball’ application in field.

Use of resistant or tolerant varieties when available.

Crop rotation with non-host dry season crops such as cowpea, groundnut, onion, pigeon pea, sorghum, soybean, sweet potato and tobacco (Babatola, 1979), mungbean, black gram and sesame (Maung, 2011), Egyptian clover (Youssef & Eissa, 2014).

Including green manure crops in crop rotation as trap crops (e.g. Aeschynomene afraspera, Sesbania rostrata) can reduce H. oryzae population in soil and add soil nitrogen as an additional benefit (Germani et al., 1983; Hendro et al., 1992; Prot et al., 1992).

Prolonged dry fallows (at least 12 months) after crop rotation can help decreasing soil population densities (Siddiqi, 1973; MacGowan, 1979). Weed management in rice fields during the growing season and in the absence of rice can reduce nematode populations.

Other cultural measures include tillage and mechanical disturbance, thermal control such as soil solarization of nursery beds and burning of stubble in the field, and incorporation of organic manures (Fortuner & Merny, 1979; Abd-Elbary et al., 2012; Youssef & Eissa, 2014; Peng et al., 2018).

Phytosanitary risk

The warmer regions of the European Union are expected to be suitable for establishment (Jeger et al., 2018). Using a CLIMEX model to study the potential establishment of H. oryzae in new areas Singh et al. (2022) projected that H. oryzae could establish in the Mediterranean area, although this area was less favourable for the pest than more tropical and subtropical regions. H. oryzae could potentially have an economic impact on rice production in the EPPO region.

Phytosanitary measures are especially relevant for plants for planting with roots of Oryza sativa, and possibly for growing medium on its own or associated with plants for planting. Potential phytosanitary measures identified by Jeger et al. (2018) against Hirschmanniella spp. include pest free production site with inspection, testing and soil treatment. In addition, for similar organisms associated with plants for planting or growing medium, EPPO recommends options such as pest free area, pest free place of production, pest free production site, as well as cleaning of used machinery and vehicles.

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CABI and EFSA resources used when preparing this datasheet

CABI (2021) Datasheet on Hirschmanniella oryzae (rice root nematode). CABI Compendium. https://doi.org/10.1079/pwkb.species.27867

Jeger M, Bragard C, Caffier D, Candresse T, Chatzivassiliou E, Dehnen-Schmutz K, Gilioli G, Gregoire J-C, Anton J, Miret J, MacLeod A, Navajas Navarro M, Parnell S, Potting R, Rafoss T, Rossi V, Urek G, Van Bruggen A, Van der Werf W, West J, Winter S, Kaluski T & Niere B (2018) Pest categorisation of Hirschmanniella spp. Scientific Opinion on the pest categorisation of Hirschmanniella spp. EFSA Journal 16, e05297, 31 pp.

This datasheet was prepared in 2023 by  Dr. ZTZ Maung (Kearney Agricultural Research and Extension Center (Parlier), UC Riverside, California, USA). Her valuable contribution is gratefully acknowledged.

EPPO (2024) Hirschmanniella oryzae. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-27)

This datasheet was first published online in 2023. It is maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.