Rev 03/02/2026
Chromadorea Rhabditida Aphelenchina Aphelenchoidea Aphelenchoididae Aphelenchoidinae
Aphelenchoides oryzae Yokoo, 1948
Synonyms
Originally described as the causal agent of white tip of rice by Yokoo (1948) and later synonumized with A. besseyi by Allen (1952)
Recently proposed as reinstated bu Subbotin et al., 2021).
However, the classification of A. besseyi based on morphological characters is not well supported by an integrated approach including both molecular and phylogenetic analysis. Ratherr, A. besseyi sensu lato appears to be a species complex with several cryptic species that are not well delimited by morphology (Subbotin et al., 2021).
Species delimitation among A. besseyi sensu lato. populations is important for phytosanitary purposes and for the selection of crop cultivars resistant to these nematodes. For example, A. besseyi sensu stricto parasitizes only strawberry (Olivieria et al., 2019). whereas A. besseyi sensu lato has a much wider host range. Conseqquently, Subbotin et al (2021) proposed the reinstatemnt of A. oryzae, which was originally described by Yokoo (1948) as the causal agent of white tip of rice but later synonymized with A. besseyi by Allen (1952). Subbotin et al., (2021) also proposed A. pseudobesseyi and A. pseudogoodeyi for variants of A. besseyi sensu lato that infect cotton and soybeans (Scheck, 2021)..
Note: Due to the uncertainty regarding the identity of the nematode species reported as Aphelenchoides besseyi in earlier studies, the species in those studies will be characterized herein as Aphelenchoides besseyi sensu lato.
Based on taxonomic studies, the foliar nematode populations with a stellate tail terminus on strawberry, rice and ornamental plants have been identified in the USA for decades as A. besseyi during routine nematological analyses for plant problems, certification, regulatory and nematode management purpose (Fortuner, 1970; Subbotin et al., 2021). However, recent phylogenetic relationships among populations from various hosts and geographical areas, inferred from analyses of 18S rRNA, 28S rRNA and partial COI gene sequences, indicate that populations of A. besseyi sensu lato from strawberry and those from rice and other ornamental plants group in separated clades in the phylogenetic trees. That supports the establishment of the strawberry, rice and ornamental plant populations as separate species (Subbotin et al., 2021)
Characteristics of Aphelenchoides oryzae:
Female:
Male:
Ref: Fortuner, 1970; Subbotin et al., 2021; Yokoo, 1948)
From Franklin and Siddiqi, 1972
The nematode has a slender stylet with small, distinct knobs.
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
White tip disease caused by Aphelenchoides oryzae, is an economic problem in many countries. Recent detections of this nematode in California have sparked the concern of California's rice industry.
B-rated pest in California Nematode Pest Rating System (Martin, 2026).
From 1959 to 1996, A. oryzae (then identified as A. besseyi sensu lato) was detected only twice in California by CDFA Nematologists. Attempts to find the nematode again from the same field were unsuccessful. A survey of the state by CDFA for the presence or absence of A. besseyi sensu lato in California paddy rice was initiated in 1997. It was intended that this survey would provide a sound basis for certifying California paddy rice free of A. besseyi sensu lato, and thereby, eliminate the requirement by the government of Turkey for methyl bromide treatments of export shipments. Sampling was designed to detect the presence of the nematode at the county or rice growing region level and 170 samples were collected.
During the 1997 survey, one confirmed and three suspected findings of A. besseyi sensu lato resulted in four samples collected from two counties. These samples tested negative when examined a second time. However, the government of Turkey required that batches of rice intended for shipment to that country should be sampled and certified to be free of the nematode. Between 1998 and 2001, A. besseyi sensu lato has been found in three such export loads. Those shipments were rejected, resulting in millions of dollars in losses.
Feeds at leaf tips and growing points in rice.
Rice is the most important host world wide. However, with the new delimitation of the species, the host list is incomplete
Ecophysiological Parameters:
Aphelenchoides oryzae is seed-borne ectoparasite rice. Nematodes in dry rice seeds are iin anhydrobiosis and are activated by rehydration. Hoshino and Togashi (2020) demonstrated that survival rate in dry rice seeds was lower at 20 and 25 C than at −5 to 10 C after storage for 190 days. No nematodes survived a storage period of 1313 days at 20 and 25�C.
However, when rice seeds were held at 5 C, the survival rate of nematodes decreased during a period of 7315 days. In storage at −30 C, nematode survival was not affected during a period of 6485 days. After storage at −30 C for 6546 days, 96% of rice seeds germinated; 60-96% of seeds germinated after storage at 5 C for 6610-7373 days. Therefore, Hoshino and Togashi (2020) postulated that low temperature storage of rice seeds would not signicicantly disrupt the pathogenicituy of A. oryzae on rice.
Anhydrobiotic in dry tissues, under hulls of rice grains; viable after 3 years.
This nematode is not thought to survive long periods in soil between crops (Cralley and French, 1952).
This nematode is mainly ectoparasitic feeding on young tissue. At the end of the growing season many nematodes are in a state of cryptobiosis under the hulls of seed (Taylor, 1969).
Seed infected with Aphelenchoides besseyi sensu lato is planted and the nematodes become active and are attracted to the meristematic areas. During early growth, Aphelenchoides besseyi sensu lato is found in low numbers within the folded leaf sheath, feeding ectoparasitically around the apical meristem (Todd and Atkins, 1958). A rapid increase in nematode numbers takes place at late tillering and is associated with the reproductive phase of the plant. Nematodes are able to enter the spikelets before anthesis and feed ectoparasitically on the plants reproductive structures. As grain filling and maturation proceed, reproduction of the nematode ceases, although the development of third stage juveniles to adult continues until the hard dough stage.
The population of nematodes is predominately adult female which are normally amphimictic, although parthenogenetic reproduction has been reported (Sudakova and Stoyakov, 1967).
These nematodes coil and aggregate in the glume axis.
The optimum temperature for oviposition and hatch is 30C.
At 30C the life cycle is approximately 8-12 days and no development occurs below 13C (Sudakova, 1968).
Aphelenchoides besseyi sensu lato slowly desiccate as kernel moisture is lost. They become anhydrobiotic dormant, and are able to survive in a quiescent state on infested seed for long periods of time, from 8 months to 3 years (Cralley, 1949; Yoshi and Yamamoto, 1950). Survival is enhanced by aggregation and a slow rate of drying (Huang and Huang, 1974), but the infectivity of the nematode is reduced as seed age increases (Cralley and French, 1952).
Diseased plants have reduced vigor and height. Infected panicles are shorter, with fewer spikelets and a smaller proportion of filled grain. In severe infections, the shortened flagleaf is twisted and can prevent the complete extrusion of the panicle from the boot (Todd and Atkins, 1958). The grain is small and distorted and the kernel may be discolored and cracked (Uebayashi et al., 1976).
Infected plants mature late and have sterile panicles borne on tillers produced from high nodes. In the rice seed-bed, emergence of severely infected seedlings is delayed and germination is low. The most conspicuous symptoms occur at the tillering stage (Taylor, 1969).
Yield loss from the white tip nematode varies widely, with some sources citing average losses of 10%�30%, while severe cases on susceptible varieties have reported losses as high as 71%. Factors like the rice cultivar, environmental conditions, and the specific management practices in place all influence the extent of yield reduction, which can range from minimal damage to over 70% loss (CABI, 2025)
Experiments have shown that different varieties of rice are affected to different degrees of infestation. Yields have been reported to be reduced by 17-54% in susceptible varieties and 24% in resistant (Atkins and Todd, 1959).
Host Plant Resistance, Non-hosts and Crop Rotation alternatives:
Hot water treatment of seed can be used to destroy this nematode infecting the seeds (Atkins and Todd, 1959). Pinherio et al. (1997), found that thermal wet treatment was the most effective. Aphelenchoides besseyi sensu lato was not recovered from rice seeds which received hot water treatment at 55-60C for 15 minutes, but was observed in seed subjected to hot water treatment at 50C (Gergon and Prot, 1993). Lower temperatures (52-53C for 15 minutes) for hot water treatment have been reported (Crawley, 1959; Tenente et al., 1994). At temperatures reported for controlling A. besseyi, no effect on seed germination or viability was reported if seed was planted quickly. Chemical treatments of seed have also been reported as being effective in controlling A. besseyi. Benomyl applied as a seed treatment reduced average numbers of nematodes (Gergon and Prot, 1993; Templeton et al., 1971). Thiabendazole has also been reported as an effective seed treatment (Tenente and Manso, 1994). Carbofuran (Tenente and Manso, 1994; Todd and Atkins, 1959) and aluminum phosphate fumigation (Tenente et al., 1994), are not effective chemical seed treatments for A. besseyi.
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CABI Compendium. 2025. Aphelenchoides besseyi (rice leaf nematode)
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