Intraspecific Variability within Globodera tabacum solanacearum and Selection for Virulence Against Flue-Cured Tobacco

The tobacco cyst nematode (TCN), Globodera tabacum solanacearum [(Miller and Gray, 1972) Behrens 1975] Stone 1983, is one of the most economically important pests of flue-cured tobacco (Nicotiana tabacum L.) in Virginia. Although TCN has been reported from other countries, the geographical distribution of G. t. solanacearum within the United States is limited to Virginia, North Carolina, and one county in Maryland. Approximately 30% of the tobacco acreage in Virginia is infested; average yield reduction is 15%, but complete crop failure can occur. The objectives of this research were to examine intraspecific variability within G. t. solanacearum and to evaluate the relative adaptability of G. t. solanacearum on a resistant (NC567) and a susceptible (K326) flue-cured tobacco cultivar. Nineteen geographic isolates of G. t. solanacearum, one isolate each of G. t. virginiae and the Mexican cyst nematode (G. "mexicana"), two isolates of G. t. tabacum, and five Heterodera species were characterized by DNA fingerprinting using the RAPD-PCR technique. Reproducible differences in fragment patterns allowed similar differentiation of the isolates and species with each primer. Hierarchical cluster analysis was performed to illustrate the relatedness between nematode isolates and species. In contrast to reports in the literature, we found a Miller isolate of G. "mexicana" to cluster more closely with G. t. solanacearum than with G. t. tabacum or G. t. virginiae. Although no pathotype differences have been found within G. t. solanacearum, the average Jaccard's similarity index among isolates of G. t. solanacearum was 74%, representing greater variation than that observed across different pathotypes of the closely related potato cyst nematode, Globodera pallida. This result suggests that the emergence of resistance-breaking biotypes is more likely than previous research suggests. If a new pathotype is reported, a RAPD marker associated with virulence against a specific host resistance gene could prove to be a valuable tool in population diagnosis, resistance screening, and overall TCN management. One isolate of G. t. solanacearum was cultured on a resistant (NC567) and a susceptible (K326) flue-cured tobacco cultivar over five generations. Variable TCN reproduction was observed on both cultivars over each generation. This variability in reproduction could be attributed to differences among generations in the time interval between inoculation and cyst extraction, temperature, possible diapause effects, and/or daylength. Ninety-eight cysts were produced in the fifth and final generation compared to the 14 to 50 cysts produced during each of the previous four generations. Increased reproduction on the resistant variety suggests that increased virulence might be selected, but research involving additional generations would need to be carried out in order to conclude whether or not TCN virulence is being selected.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Plant Pathology, Physiology, and Weed Science

Department dc:contributor.department

Plant Pathology, Physiology, and Weed Science

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2002

Author dc:creator

• Syracuse, Aaron James

Chairs dc:contributor.committeechair

• Johnson, Charles S.
• Eisenback, Jonathan D.

Committee members dc:contributor.committeemember

• Nessler, Craig L.
• Wilkinson, Carol A.

• RAPD
• Virulence
• Tobacco Cyst Nematode
• Globodera tabacum solanacearum

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-10282002-083558

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/35515