Discovery of Potato Rot Nematode, Ditylenchus destructor, Infesting Garlic in Ontario, Canada

Potato rot nematode, Ditylenchus destructor Thorne, 1945, is a serious nematode pest in a number of root and tube crops, primarily in potatoes, and is an internationally quarantined pest (2). In garlic, it was only reported in Japan (3). In 2011, a survey was conducted for the stem and bulb nematode, Ditylenchus dipsaci (Kühn) Filipjev in Ontario, Canada. PCR analysis revealed that a population of Ditylenchus from one garlic (Allium sativum) bulb sample in a 0.81-ha field (2-acre) in the Ottawa area had a significantly longer ITS1 (approximately 100 bp) than that of D. dipsaci. Subsequent morphology and DNA sequencing concluded that the population was Ditylenchus destructor, a quarantine species in Canada. Twenty females and twenty males were fixed and permanently mounted for morphological studies. The main diagnostic characters matched the description of D. destructor by Thorne (4). The female stylets had strong knobs, 11.1 ± 0.9 (10 to 12) μm long, lateral fields with six distinct lines in the middle section of the body, excretory pore 4.7 ± 1.3 (3 to 6) μm posterior to the hemizonid, esophageal base bulb overlaps dorsally with the intestine, post-vulval uterine sac extends up to two-thirds of the vulva-anus distance, and tail terminus finely rounded. A total of 20 nematode individuals were used for the molecular studies. They had 5-bp differences with the ITS1 (GenBank Accession No. EF208210; 650 bp) sequence of an isolate from Sihong County, China. The sequence of the partial 18S gene (GenBank Accession No. AY593912; 864 bp) was identical to the sequence of an isolate of D. destructor in the Netherlands. The detection of stem and bulb nematode was also confirmed from the field. Infested garlic plants were stunted and the basal bulbs became dark and somewhat rotten. Prior to this finding in Canada, D. destructor was only reported in a few isolated locations in the province of Prince Edward Island (PEI) in 1946 (1). The nematodes in PEI were effectively controlled. Another suspected case in British Columbia was not confirmed since the infested field had been known to be infested with D. dipsaci. To our knowledge, this is the first report of D. destructor on the mainland of Canada. The infested field has been subjected to strict quarantine measures to prevent the spread of the pest. Reference: (1) A. D. Baker et al. Sci. Agric. 26:138, 1946. (2) EPPO. No. 123. Data Sheets on Quarantined Organisms. Bulletin OEPP/EPPO Bull. 8, 1978. (3) T. Fujimura et al. Jpn. J. Nematol. 8:22, 1989. (4) G. Thorne. Proc. Helminthol. Soc. Wash. 12:27, 1945.