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Heterodera elachista

Heterodera elachista (Nematoda: Heteroderidae)

Japanese rice cyst nematode

 

Why: The cyst nematode, Heterodera elachista, was originally described in Japan in 1974. Until recently, it was known to occur in Asia only, affecting upland rice crops. In October 2012, its presence was detected in Italy on a maize crop. Because this was the first time that H. elachista was recorded in the EPPO region and on a new and economically important host plant, the EPPO Secretariat decided to add this nematode to the EPPO Alert List.

Where: Until its discovery in 2012 in Italy (1 maize field in Emilia-Romagna region), H. elachista was known to occur in Asia only.
EPPO region: Italy (no longer found in Emilia Romagna but another outbreak was detected in 2016 in Lombardia; transient, under eradication).
Asia: China (Guangxi, Hunan, Ningxia), Iran, Japan (from Northern Honshu to Kyushu).
Maize roots with cysts of Heterodera elachista. All pictures were kindly provided by Pablo Castillo (Institute for Sustainable Agriculture, Córdoba, ES)
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On which plants: rice (Oryza sativa), and maize (Zea mays). In Asia, H. elachista has only been reported in rice crops. As is the case for most rice cyst nematodes (except H. oryzae), H. elachista cannot withstand an extended flooding period and is mainly found on upland rice or on lowland rice where there is little or no water control. Experiments carried out in Italy on potted plants of rice and maize have shown that both species were suitable host plants for H. elachista.

Damage: Rice plants infested by H. elachista can be severely stunted and chlorotic and usually produce fewer tillers. Root growth can be reduced, infested roots becoming brown or black. If soils are heavily infested rice seedlings may die. It was estimated that H. elachista can decrease rice yield by 7 to 19% and has the most severe impact during the later stages of plant growth.
In their paper, De Lucas et al. (2013) mentioned that the affected maize field in Italy presented patches of plants showing severe decline and stunting, with heavily infested plants displaying significant proliferation of short lateral roots. Brown cysts and white lemon-shaped females could be observed on the root surface of affected plants, as well as in the soil.
H. elachista has sedentary endoparasitic habits. Cysts are persistent tanned sacs derived by the female body and contain the eggs. Cysts persist in soil for many years. Second-stage juveniles (J2) emerge from the cysts, penetrate host roots and establish a specialized feeding site (syncytium) in the central cylinder of roots (stele). They develop into swollen females, which retain the eggs and produce large egg masses. Females rupture the root cortex and protrude from the root surface. At the end of the reproductive phase, females die and become rounded dark or black cysts. H. elachista is morphologically close to H. oryzae, H.oryzicola and H. sacchari, and its identification requires the use of several techniques (e.g. morphological, biochemical, molecular). The life cycle of H. elachista was studied in China both in the laboratory and in a rice field. Results showed that the development of H. elachista is slow below 20°C, and is favoured by relatively high temperatures. At 30°C, the complete life cycle took 22 days (however, the English abstract of the paper from Zhong et al., 2012 does not mention whether these values are referring to air or soil temperatures).

Dissemination: Natural spread is very limited, as juveniles can only move over short distances when attracted towards roots in the soil. As in the case of other cyst nematodes, H. elachista can spread into new areas as cysts, carried with plants, soil or soil attached to plants, machinery or any other material.

Pathway: Plants for planting, soil, soil attached to agricultural machinery or other material.

Possible risks: Maize, and rice to a lesser extent, are economically important crops in the EPPO region. Although data is lacking about the economic impact of H. elachista, it cannot be excluded that this cyst nematode could have negative impacts on maize and rice yields. Data is generally lacking on possible control measures against H. elachista. However, it is likely that as for other cyst nematodes, control would probably rely on crop rotation with non-hosts. As cysts persist in soil for a long time and can be easily transported with soil and soil attached to plants or contaminated machinery or any other material, it is desirable to avoid any further spread of this nematode within the EPPO region.

Cyst and juveniles
of H. elachista.

Sources
Bridge J, Starr JL (2007) Plant nematodes of agricultural importance. A color handbook. Academic Press, 152 pp.
De Luca F, Vovlas N, Lucarelli G, Troccoli A, Radicci V, Fanelli E, Cantalapiedra-Navarrete C, Palomares Rius JE, Castillo P (2013) Heterodera elachista the Japanese cyst nematode parasitizing corn in Northern Italy: integrative diagnosis and bionomics. European Journal of Plant Pathology 136(4), 857-872.
Ding Z, Namphueng J, He XF, Peng DL, Huang WK (2012) First report of the cyst nematode (Heterodera elachista) on rice in Hunan Province, China. Plant Disease 96(1), p 151.
Ding Z, Namphueng J, He XF, Wu MM, Hong H (2012) [Life cycle and infection characteristics of rice cyst nematode, Heterodera elachista Ohshima in rice]. Chinese Journal of Rice Science 26(6), 746-750 (in Chinese).
INTERNET
The Society of Nematologists. Exotic Nematode Plant Pests of Agriculture and Environmental Significance to the United States. http://nematode.unl.edu/pest68.htm
Nobbs JM, Ibrahim SK, Rowe J (1992) A morphological and biochemical comparison of the four cyst nematode species, Heterodera elachista, H. oryzicola, H. oryzae and H. sacchari (Nematoda: Heteroderidae) known to attack rice (Oryza sativa). Fundamental and applied Nematology 15(6), 551-562.
NPPO of Italy (2013-12, 2016-12).
Oshima Y (1974) Heterodera elachista n. sp., an upland rice cyst nematode from Japan. Japanese Journal of Nematology 4, 51-56.
Shimizu K (1976) [Influence of the upland rice cyst nematode, Heterodera elachista, on the yield of the upland-cultured paddy rice]. Japanese Journal of Nematology 6, 1-6 (in Japanese).
Tanha Maafi Z, Subbotin SA, Moens M (2003) Molecular identification of cyst-forming nematodes (Heteroderidae) from Iran and a phylogeny based on ITS-rDNA sequences. Nematology 5(1), 99-111.
Zhuo K, Song HD, Wang HH, Tao Y, Zhang HL, Lu XH, Huang JL, Liu ZM, Liao JL (2014) [Occurrence of Heterodera elachista in Guangxi region and its intra-species heterogeneity in rDNA-ITS region. Chinese Journal of Rice Science 28(1), 78-84 (in Chinese).

EPPO RS 2014/045, 2017/042

Panel review date 2017-03
Entry date 2014-03

 

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