First Report of the Potato Cyst Nematode, Globodera rostochiensis, on Potato in the Azores, Portugal

In Portugal, growing potatoes (Solanum tuberosum) has both social and economic importance. Because potato cyst nematodes (PCN) are major pests of potatoes, their presence in these areas could pose a risk to its production. Therefore, the National Survey Plan for PCN that was implemented in 2010 is still ongoing. This survey aims for the early detection of PCN to provide tools to control and manage initial PCN infestations below the damage threshold level, while avoiding their dispersal within both national and EU territories. During the 2018 National Survey in the potato production areas of the São Miguel Island (Azores), six bulk soil samples of 1 kg from a small field cultivated for household consumption in Nordeste County were investigated. A subsample of 500 g from the bulk sample was dried, and cysts were extracted using a Fenwick can. Dried cysts were hydrated and cut to release eggs, and hatched J2 were collected for morphometric analysis. The identification of PCN was based on a combination of n = 30 cysts and n = 90 J2 measurements. The cyst length excluding neck (L) was 493.658 ± 89.377 μm, width (W) was 474.090 ± 93.569 μm, the L/W ratio was 1.051 ± 0.115, and neck was 110.894 ± 26.353 μm. The number of cuticular ridges between the vulva and the anus was higher than 20. The distance from vulva to anus was 60.15 ± 6.7 µm with the Granek’s ratio ranging from 1.26 to 4.99. The vulva fenestrate was 25.13 ± 6.7 µm in diameter and anus visible in almost all specimens, with a V-shaped mark. The stylet length of J2 was 23.14 ± 1.8 µm with rounded knobs. Body length was 449.79 ± 30.3 µm, and average true and hyaline tail length were 50.92 ± 6.4 µm and 26.50 ± 4.3 µm, respectively. The overall morphometric values were within the range described in PM 7/40(4) (EPPO 2017) for Globodera rostochiensis. The above morphological characterization was also confirmed using a sequence-specific multiplex PCR (Bulman and Marshall 1997) described in PM7/40(4) (EPPO 2017) and conventional PCR of 18S rDNA (SSU), 28S rDNA (LSU), and cytochrome oxidase subunit I (COI) as described in PM7/129(1) (EPPO 2016). The nucleotide sequences (MN226947, MN238768, and MK798162) showed a similarity of 99 to 100% with available isolates of G. rostochiensis in NCBI database. A pathogenicity test was carried out in the greenhouse by planting tubers of the susceptible cultivar Desirée in four plastic pots of 15 cm diameter. Pots were inoculated with an initial population density of 5 J2 and eggs per gram of soil and harvested after 90 days. A final population (Pf) of mean of x¯ = 23.3 J2 or eggs per gram of soil was obtained, resulting in a reproduction factor (R=Pf/Pᵢ) of 4.66 ± 0.86. According to the European Commission Regulation EC 690/2008 updated by implementing regulation EU 2016/873, the Azores islands are recognized as protected zones for G. rostochiensis and G. pallida. This is the first report of the presence of G. rostochiensis in the Azores islands. Research will focus more on the spatial distribution of the nematodes, and based upon it integrated control methods will be devised including strict phytosanitary measures to prevent spread and ensure further the Azores as a PCN protected zone.