Aphelenchoides besseyi

Aphelenchoides besseyi	Contents	Rev 03/23/2007
White Tip of Rice	Classification	Hosts
	Morphology and Anatomy	Life Cycle
Return to Aphelenchoides Menu	Economic Importance	Damage
	Distribution	Management
Return to Aphelenchoididae Menu	Feeding	References
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Classification:

      Tylenchida
       Aphelenchina
         Aphelenchoidea
          Aphelenchoididae
           Aphelenchoidinae
        Aphelenchoides besseyi

Morphology and Anatomy:

Drawings by M.W. Allen, photographs by P. Mullin

Aphelenchoides besseyi is characterized by a large metacorpus (median bulb), and esophageal glands usually overlapping dorsally.

Dorsal esophageal gland opens into lumen of esophagus in metacorpus, just anterior to the pump chamber.

Subventral esophageal glands open into lumen of esophagus in metacorpus, posterior to the pump chamber.

From Franklin and Siddiqi, 1972

The nematode has a slender stylet with small, distinct knobs.

The tail has a terminal spike or mucro.

Females: 0.66-0.75 mm long and slender.

Males: are as numerous as females.

Male reproductive structures have no bursa and the spicules have the typical rose-thorn shape of the genus (Franklin and Siddiqi, 1972).

Allen provided a key to the four important species related to A. fragariae. The key is useful in that it provides characteristics to separate the four closely related species (Allen, 1952).

Sanwal (1961) listed 33 species and provided a key.

Aphelenchoides besseyi is widely distributed and occurs in most rice growing areas (Ou, 1985). The known distribution of A. besseyi on rice includes; Australia, Ceylon, Comoro Islands, Cuba, El Salvador, Hungary, India, Indonesia, Italy, Japan, Madagascar, Mexico, Pakistan, Philippines, Taiwan, Thailand, former USSR, and in most countries of central and West Africa (Ou, 1972; Franklin and Siddiqi, 1972).

Aphelenchoides besseyi was first found in Japan in 1915. In the USA the disease was first noticed in the southern United States in 1935 but was attributed to a nutrient deficiency (Ou, 1972).

Aphelenchoides besseyi has been reported in many Southern U.S. states that produce rice.

White tip disease caused by Aphelenchoides besseyi, is an economic problem in many countries. Recent detections of this nematode in California have sparked the concern of California's rice industry.

From 1959 to 1996, A. besseyi was detected only twice in California by CDFA Nematologists: once in 1959, in a quarantine strawberry sample originating in Oregon, and the second time in 1963 in a fungal culture collected in Butte county. 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 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, 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 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 has been found in three such export loads. Those shipments were rejected, resulting in millions of dollars in losses.

Aphelenchoides besseyi was detected in paddy rice shipments, once each in 2001 and 2002, and in 11 samples in 2005. It has been detected only in the northern counties (Butte and Sutter), and continues its status as a quarantine pest of very limited distribution in California (J. Chitambar, CDFA, personal communication).

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Economic Importance:

A-rated pests in California.

At the state level there are no formal quarantine regulations implemented against A. besseyi. There are no prohibitions for the import of rice seed into California from other states within the US. At the federal level, federal regulations have prohibited the import of seed and paddy rice into the US since November 23, 1933. Milled rice can enter California.

Paddy rice exported to Turkey requires certification for freedom from A. besseyi according to the Turkish Government pest control requirements. In compliance with the Turkish government, certification is given on a per shipment basis; each shipment has to be sampled and found free of A. besseyi before it can be certified and shipped to Turkey.

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Feeding:

Mainly ectoparasitic on buds.

Feeds at leaf tips and growing points in rice.

May feed endoparasitically in leaf mesophyll.

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Hosts:

Rice is the most important host world wide.

On strawberry A. besseyi is the causal agent of 'summer dwarf' or 'crimp' in the United States and Australia.

Other host plants include; onion, garlic, sweet corn, sweet potato, soybean, yan chinese cabbage, sugar cane, horseradish, lettuce, millet, many grasses, orchids, wishbone, chrysanthemum, marigold, mexican sunflower, african violets, rubber plant, Hibiscus brachenridgii, and hydrangea (Franklin and Siddiqi, 1972).

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Life Cycle:

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 is planted and the nematodes become active and are attracted to the meristematic areas. During early growth, A. besseyi 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 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).

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Damage:

Feeding at leaf tips in rice results in whitening of the top 3-5 cm of the leaf, leading to necrosis (described as "White Tip" of rice by Yokoo, 1948). There is also distortion of the flag leaf that encloses the panicle.	Photo from Society of Nematologists slide set, 1980.
	Diseased plants are stunted, lack vigor and produce small panicles. Affected panicles show high sterility, distorted glumes and small and distorted kernels (Ou, 1972).

In the seed-bed, emergence of severely infected seedlings is delayed and germination is low.

The most conspicuous symptoms occur at the tillering stage (Taylor, 1969).

Yields of rice may be reduced 50%.

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).

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Management:

Preventative Measures - Aphelenchoides besseyi infestations can be avoided by using nematode-free seeds and planting in nematode-free fields (Taylor, 1969; Hudma et al., 1994).

Resistant Cultivars - The planting of resistant cultivars have strongly reduced yield losses caused by A. besseyi. However, resistant varieties may not be compatible with California production practices or market requirements. Rice varieties differ greatly in susceptibility to A. besseyi (Crally and French, 1952; Atkins and Todd, 1959).
Seed Treatment - Although there is some risk of injury to germination (Taylor, 1969), the most effective means of controlling A. besseyi is through seed treatments:

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 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.

Chemical Control - The timing of field applications of chemicals is critical for the control of A. besseyi. Benomyl applied one day after nematode inoculation was more effective than when applied as a seed treatment. Total control was achieved when benomyl was sprayed as a seed treatment followed by two field sprayings. Control was increased when benomyl was applied during the nematode infestation stage as opposed to later in their life cycle when the nematode was feeding in the apical meristem (Gergon and Prot, 1993). Carbofuran applied in floodwater failed to control A. besseyi even immediately after inoculation (Gergon and Prot, 1993).
Cultural Practices - There are reports that rice seeded in water has trace white tip infection, but if sown in dry soil and flooded later (usual practice in many areas), 60% of the crop may be infected. Presumably that strategy would be most effective when the soil was infested and clean seed used; less effective if infested seed was planted.

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References:

Allen, M.W. 1952. "Taxonomic status of the bud and leaf nematodes related to Aphelenchoides fragariae (Ritzema Bos, 1891)." Proc. Helminth. Society of Washashington. 19:108-120.

Bridge, J., M. Luc and R.A. Plowright. 1990. "Nematode parasites of rice." Pp. 69-108, M. Luc et al. (eds.), Plant parasitic nematodes in subtropical and tropical agriculture. Wallingford, UK: CAB International.

Cralley, E.M. 1949. "White tip of rice." Phytopathology. 39:5.

Cralley, E.M., and R.G. French. 1952. "Studies on the control of white tip of rice." Phytopathology. 42:6.

Franklin, M.T. and M.R. Siddiqi. 1972. Aphelenchoides besseyi. Commonwealth Institute of Helminthology Descriptions of Plant-parasitic Nematodes Set 1, No. 4.

Gergon, E.B. and J.C. Prot. 1993. "Effect of benomyl and carbofuran on Aphelenchoides besseyi on rice." Fundamentals of Applied Nematology. 6:563-566.

Huelma, C.C., J.C. Prot, S.D. Merca, and T.W. Mew. 1994. "Aphelenchoides besseyi in irrigated upland and lowland rice during dry and wet season." International Rice Research Notes. 19 (3):30.

Ou, S.H. 1985. Rice Diseases (2nd edition). New England: Commonwealth Mycological Institute.

Pinheiro, F.P., R.P. Vianello, F.S. Ebeidalla, and R.C.V. Tenente. 1997. "Thermal seed treatments to eradicate Aphelenchoides from Brachiaria dictyoneura." Nematologia Brasilerira. 21 (1): 92-97.

Sanwal, K.C. 1961. " A key to the species of the nematode genus Aphelenchoides Fischer, 1894." Canadian Journal of Zoology. 39:143-148.

Taylor, A.L. 1969. "Nematode parasites of rice." Pp. 264-268, J.E. Peachey (ed.), Nematodes of Tropical Crops. Albans, Herts, England: Commonwealth Bureau of Helminthology.

Tamura, I., and K. Kegasawa. 1958. "Studies on the ecology of the rice nematode, Aphelenchoides besseyi Christie. II. On the parasitic ability of rice nematodes and their movement into hills." Japanese Journal of Ecology. 8:37-42.

Templeton, G.E., T.H. Johnston and J.T. Daniel. 1971. Benomyl controls rice white tip disease." Phytopathology. 61:1522-1523.

Tenente, R.C.V., M.M.V.S. Wetzel, E. S. Manso, and A.S. Marques. 1994. "Survival of Aphelenchoides besseyi in infested rice seeds stored under controlled conditions." Nematologia Brasiliera. 18 (1): 85-92.

Tenente, R.C., and E.S. Manso. 1994. "Chemical and heat treatments of rice seeds infested with Aphelenchoides besseyi." Nematologia Brasileira. 18 (1): 28-34.

Yoshi, H., and S. Yamamoto. 1950. "A rice nematode disease 'Sencha Shingane Byo'. II. Hibernation of Aphelenchoides oryzae." Journal of Faculty of Agriculture, Kyusha University. 9:223-233.