Potato

Samples should be sent to a nematode diagnostic lab where nematodes will be extracted and identified.

Soil surveys can be conducted at any time of year following production of a susceptible crop, as eggs in cysts remain viable in soil for many years. Soil surveys conducted after harvest are preferred, to take advantage of soil mixing that occurs due to harvest. Symptom surveys should be conducted in potato and tomato fields during the growing season.

In the decades since its discovery in 1941 on Long Island, New York, the distribution of G. rostochiensis has remained very limited in the United States. Globodera rostochiensis is under official control in the New York counties of Cayuga, Livingston, Nassau, Orleans, Seneca, Steuben, Suffolk, and Wayne, where quarantine measures and crop rotations have successfully controlled and contained the nematode. Survey efforts should therefore be focused in these parts of New York, particularly fields that are suspected to be exposed to G. rostochiensis. When surveying other areas, focus survey efforts where potatoes and tomatoes have been planted consecutively for three or more years.

Conduct visual inspection for G. rostochiensis by searching for symptoms such as stunting, yellowing, and crop failure. These infestation symptoms occur in a spotty manner in the field, and the affected areas tend to elongate in the direction of cultivation due to spread of the nematode by machinery. Sites that are especially likely to be infested with G. rostochiensis include dumping grounds containing debris from graders or storage areas, edges where equipment is turned during cultivation and plowing, entrances and exits, and low spots in the field.

The pattern and number of samples to be taken will vary depending upon the likelihood of infestation, acreage involved, personnel available, and other factors, with details outlined in the Golden Nematode Program Manual. Soil should be scooped into paper sample bags for collection. Soil should be dry when processed to discover nematode cysts.

Morphological: Characteristics of second-stage juveniles, females, and cysts (Baldwin and Mundo-Ocampo, 1991; Subbotin et al., 2010).

Molecular: Immunological, protein, and DNA-based techniques are available, including RAPD and RFLP analyses.

There are PPQ CPHST-validated conventional PCR (Skantar et al., 2007) and real-time PCR methods to detect G. rostochiensis, G. pallida, and G. tabacum (Nakhla et al., 2008; Nakhla et al., 2010; Yu et al., 2011). A validated work instruction for the real-time PCR method developed by Nakhla et al., (2010) is available.

Morphological characters and keys to differentiate between potato cyst nematode species can be found in various publications (Golden and Ellington, 1972; Handoo et al., 2012; Lax et al., 2014; Mulvey and Golden, 1983; Spears, 1968; Subbotin et al., 2010). RT-qPCR assays have been developed to distinguish between and quantify Globodera species and evaluate egg viability (Madani et al., 2008; Mimee et al., 2017; Pylypenko et al., 2005; Yu et al., 2011).

Globodera rostochiensis can be mistaken for G. pallida, G. tabacum, and G. ellingtonae. However, G. tabacum primarily infests tobacco and is unlikely to be associated with potato (Skantar et al., 2007). Globodera rostochiensis, G. pallida, and G. ellingtonae infect potato and have limited distributions in the United States. Globodera species can be differentiated using in-depth morphological or DNA-based analysis (Baldwin and Mundo-Ocampo, 1991; Nakhla et al., 2008; Nakhla et al., 2010; Skantar et al., 2007; Yu et al., 2011). Additionally, females of G. pallida change directly from white directly to brown as they mature and die, becoming cysts, whereas females of G. rostochiensis change from white to yellow/gold to brown.