DISTRIBUTION OF MELOIDOGYNE CHITWOODI mtDNA HAPLOTYPES IN THE MAJOR POTATO PRODUCTION AREAS OF WASHINGTON STATE

Washington is ranked second in potato production in the United States based on total yield. One of the major threats to the potato industry in the Pacific Northwest (Oregon, Washington, and Idaho) is root-knot nematodes, particularly Meloidogyne chitwoodi. The distribution and genetic diversity of M. chitwoodi in the region are unknown. Eighteen tuber samples (up to ten tubers per sample) showing typical galls induced by root-knot nematodes were collected from the top six potato-producing counties in Washington. Species identification was performed using PCR with species-specific primers. Eighteen Meloidogyne samples were identified as M. chitwoodi whereas concomitant Meloidogyne species (M. chitwoodi and M. hapla) were found in two samples. Intraspecific variability ofM. chitwoodi was studied by sequencing the mitochondrial (mt) locus cytochrome b (cytb). Three cytb haplotypes were identified based on four segregating sites detected from an alignment of 540 sequences [each corresponding to one second-stage juvenile (J2)]. Haplotype 1 represented 71% ofM. chitwoodi J2 (382 sequences), followed by haplotype 2 with 19% (100 sequences), and haplotype 3 with 11% (58 sequences). All three haplotypes were identified in a sample from Quincy, Grant County, the same location from which M. chitwoodi was first described in the 1980s.