First report of Heterodera elachista on maize in Italy: addition to the EPPO Alert List
The cyst nematode, Heterodera elachista, was originally described in Japan in 1974, and until its recent detection in Italy, it was only known to occur in Asia on rice crops (Oryza sativa). In October 2012, a sample of soil and roots was collected from a commercial maize field (Zea mays cv. ‘Rixxer’) in Bosco Mesola (Ferrara province, Emilia-Romagna region) and tested for the presence of nematodes. A trial with plant protection products was being carried out by a chemical company on this maize field. In this sample, roots were heavily infested by Heterodera sp. cysts which were also present in the soil (14 eggs and J2/ml of soil). Laboratory analysis (morphology, molecular tests) was carried out by the Institute of Plant Protection (CNR, Bari) and confirmed the presence of H. elachista. Tests were also carried out on potted plants of maize (Zea mays cv. ‘PR 33’) and rice (Oryza sativa cv. ‘Baldo’) to verify their host plant status. Experiments showed that both rice and maize plants allowed feeding and reproduction of H. elachista, and confirmed that they were suitable host plants. The results of this first finding were published by De Lucas et al., in summer 2013. In September 2013, the NPPO of Italy initiated an official sampling programme in the infected maize plot and its vicinity (within a radius of 500 m). It is noted that on the infested plot, maize was grown in rotation with either soybean or winter cereals every third year, and that rice has never been cultivated. Only certified maize seeds have been used and most agricultural machinery has been managed by contractors operating in nearby farms. For the moment, it has not been possible to determine a possible pathway of introduction of H. elachista into Italy. As requested by the NPPO, the grower has sown a crop other than maize. Monitoring is ongoing to determine the distribution of the nematode and possible control measures are being evaluated.
The pest status of Heterodera elachista in Italy is officially declared as: Transient, reported in a single plot in Ferrara province. A survey is in progress to assess the actual presence and distribution of the pest.
Heterodera elachista – 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 is the first time that H. elachista is 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 Italy in 2012, H. elachista was known to occur in Asia only.
EPPO region: Italy (1 maize field in the province of Ferrara, Emilia-Romagna region; transient).
Asia: China (Guangxi, Hunan, Ningxia), Iran, Japan (from Northern Honshu to Kyushu).
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.
EPPO RS 2014/045
Panel review date -
Entry date 2014-03
Entry date 2014-03
Sources
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INTERNET
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