48 , 2017-09-08 , 国立研究開発法人 農業・食品産業技術総合研究機構 , National Agriculture and Food Research Organization (NARO)
2015年8月に北海道内の一部の圃場において，国内未発生だったジャガイモシロシストセンチュウGlobodera pallidaが初めて確認され，その蔓延防止および根絶対策を早急に実施することが求められた。しかし，国内では本線虫に対する研究蓄積が少なく，その対策は極めて困難であることが予想された。そこで本線虫に関する研究，防除対策，抵抗性品種育成等において先進的な知識や技術の蓄積があるヨーロッパの研究機関等（5機関）を訪問し，情報収集を行った。 今回訪問した3カ国（オランダ，フランス，スコットランド）とも防除対策に対する基本的な考えに大きな違いはなく，現在日本でも実施しているジャガイモシストセンチュウG. rostochiensisに対するものと同様の対策が取られていた。具体的には，土壌検診によるリスクの把握，適切な輪作体系の維持，化学農薬による密度低減，抵抗性品種の作付け，捕獲植物の利用である。また，検査を受けた正規の種イモ利用の徹底，野良ばえの除去，耕作機械や運搬車両の洗浄などの侵入・分散防止対策も重要である。しかしながら土壌検診の実施体制や防除プログラムの実施義務化などの制度面などにおいては日本とは異なる点が認められた。 土壌検診は，訪問した3カ国とも2007年のEU指令に準じた方法により，公的機関によって実施されていたが，その手法は日本よりも遙かに洗練され，特にSASAでは半自動シスト分離装置（carousel）やPCRなどを駆使し，多検体を効率的に検査できるよう工夫されていた。また，検診でシストセンチュウが発見された場合には，防除計画の策定・実施が求められるが，一定の要件を満たすことにより発生圃場の指定が解除されるderecordingの制度が設けられていた。日本においてはまず既存の検診システムに応用できるシストの種判定法を早急に開発することが必要とされているが，将来的には多検体を効率的に調査できるシステムの導入が極めて重要と考えられた。 抵抗性品種の育成については，各国とも抵抗性遺伝子を集積することによってより強い抵抗性を付与することを基本としており，2～3の抵抗性遺伝子を主に利用していた。また，抵抗性の打破を防ぐために多様な抵抗性遺伝子を利用することも重要である。抵抗性の検定は，ヨーロッパの標準法が定められていたが，育種選抜には効率化のために各育種機関で独自の簡易検定法が開発され，用いられていた。日本でも独自の抵抗性の選抜及び評価方法を開発する必要があると考えられた。 In August 2015, the pale potato cyst nematode (Globodera pallida) was found for the first time in several fields in Hokkaido Prefecture, Japan. Potato cyst nematodes (PCNs, G. pallida and G. rostochiensis) are pests under quarantine control worldwide because PCN infection causes considerable yield losses by inhibiting potato growth. In addition, the tough cuticular wall of the cyst stage of the PCN lifecycle enables the nematode eggs inside the cyst to survive for more than ten years, even in conditions of flooding, extreme drought, and low temperatures. Although urgent control measures should be put in place to eradicate G. pallida in Japan, we had a poor understanding of infestation control measures, efficient soil testing methods for detection of PCNs, and breeding programs for potato varieties resistant to G. pallida. Therefore, we visited the potato breeding companies, the inspection service centers for seed potatoes, and the research institution in European countries that had vast experience with G. pallida. These institutions were namely HZPC and the NAK (Dutch General Inspection Service) in the Netherlands, Germicopa in France, and the Science & Advice for Scottish Agriculture (SASA) and the James Hutton Institute in Scotland. HZPC and Germicopa are the world-leading potato breeding companies. NAK and SASA are general inspection services that conduct PCN testing, seed production, and certification. The James Hutton Institute is a research institute for agriculture and land use. As a result of interviews with key personnel from each company and institute, integrated management was considered the fundamental measure to control PCNs. Integrated control includes methods such as crop rotation, use of fumigants and nematicides, and the cultivation of resistant varieties and trap crops. In addition, to prevent the introduction and spread of PCNs, practices such as PCN monitoring by appropriate soil testing, use of certified seed, control of volunteer potatoes, and washing of cultivating machinery and transporter vehicles have been strictly adhered to in these countries. These integrated management measures are already commonly employed in Japan for the management of G. rostochiensis. However, we found several differences in the soil testing method and control system of PCNs. In the three countries we visited, official organizations conducted soil testing based on Directive 2007/33/EC. At NAK and SASA, an efficient and systematic cyst extraction method has been established using a “carousel,” a machine that enables automated separation of cysts from soil samples. Extractions produced by the carousel were visually inspected and if cysts were observed, the nematode species present were identified by PCR-based methods. At SASA, the majority of soil samples were directly tested by PCR based methods without prior visual observation of nematode presence. This resulted in high-throughput, rapid PCN diagnosis. If PCN was found following soil testing, the field was recorded as ‘infested’ and no seed potatoes were allowed to be grown in the field until the field was no longer considered infested. Ware potatoes were allowed to be grown on the infested field only if a control program that was officially approved was carried out. If no live PCN was detected following strict soil testing and officials approved the field as free from PCNs, the field was no longer considered infested and farmers were allowed to grow seed potatoes once more. In Japan, a system for the identification of cysts detected during conventional soil testing must be urgently established. In addition, it is necessary to introduce a high-throughput soil testing system in Japan in the future. Furthermore, it may be important to consider creating a new regulatory system that supports the efforts of the farmer to control PCNs, such as official approval once a field is no longer considered infested. In each of the countries visited, resistant potato varieties were considered as the most important component of an integrated control system for PCNs. Resistance genes conferring complete resistance against G. pallida are not yet reported, and therefore breeding of G. pallida- resistant varieties is more difficult than breeding G. rostochiensis-resistant varieties. To develop resistant varieties, the introduction of strong resistance by the pyramiding of several resistance genes was considered as a basic policy in breeding companies and institute. As a breakdown of PCN resistance had been reported in Germany, the use of multiple resistance genes derived from a wide range of closely related species was considered as a means to prevent the breakdown of PCN resistance. Variety PCN resistance strength is scored as 1?9 based on a standard method described in the 2006 EPPO Bulletin; however, the standard method is space-consuming and labor-intensive. Therefore, experimental genotypes were selected for PCN resistance at each breeding company or institute using a simplified method that employed transparent plastic cups and plastic pots that could easily be partitioned. It is important to establish a similar framework for the efficient scoring of PCN resistance and the selection of PCN resistant genotypes in Japan.