Nematodes are one of the major limiting factors in alfalfa production. Root-knot nematodes (RKN, Meloidogyne spp.) are widely distributed and economically important sedentary endoparasites of agricultural crops and they may inflict significant damage to alfalfa fields. As of today, no studies have been published on global gene expression profiling in alfalfa infected with RKN or any other plant parasitic nematode. Very little information is available about molecular mechanisms that contribute to pathogenesis and defense responses in alfalfa against these pests and specifically against RKN. In this work, we performed root transcriptome analysis of resistant (cv. Moapa 69) and susceptible (cv. Lahontan) alfalfa cultivars infected with RKN Meloidogyne incognita, widespread root-knot nematode species and a major pest worldwide. A total of 1,701,622,580 pair-end reads were generated on an Illumina Hi-Seq 2000 platform from the roots of both cultivars and assembled into 45,595 and 47,590 transcripts in cvs Moapa 69 and Lahontan, respectively. Bioinformatic analysis revealed a number of common and unique genes that were differentially expressed in susceptible and resistant lines as a result of nematode infection. Although the susceptible cultivar showed a more pronounced defense response to the infection, feeding sites were successfully established in its roots. Characteristically, basal gene expression levels under normal conditions differed between the two cultivars as well, which may confer advantage to one of the genotypes toward resistance to nematodes. Differentially expressed genes were subsequently assigned to known Gene Ontology categories to predict their functional roles and associated biological processes. Real-time PCR validated expression changes in genes arbitrarily selected for experimental confirmation. Candidate genes that contribute to protection against M. incognita in alfalfa were proposed and alfalfa-nematode interactions with respect to resistance are discussed.

Nischwitz, C, Skantar, A., Handoo, Z. A., Huit, M. N., Schmitt, M. E., and McClure, M. A. 2013. Occurrence of Meloidogyne fallax in North America, and molecular characterization of M. fallax and M. minor from U.S. golf course greens. Plant Dis. 97:1424-1430.Several species of root-knot nematodes {Meloidogyne spp.) are known to have significant presence on turfgrass in golf course greens, particularly in the western United States. Nematodes isolated from a golf course in King County, WA were identified as Meloidogyne minor based on analysis of the large ribosomal subunit (LSU 28S D2-D3 expansion segment), the internal transcribed spacers 1 and 2 (ITS rDNA), the intergenic spacer region 2 (IGS2), and the nuclear proteincoding gene Hsp90. Sequence-characterized amplified region (SCAR) primers that were originally designed to be specific for M. fallax were found to cross-react with M. minor. A population from Califomia was determined to be M. fallax based on juvenile tail morphology and analysis of the ribosomal markers and Hsp90, comprising tlie first report of this species in North America. Using trees based on Hsp90 genomic alignments, the phylogenetic relationships of these populations and known root-knot nematode species were congruent with previous trees based on ribosomal genes. Resolution of M. fallax and M. chitwoodi using Hsp90 was equivalent to species separation obtained with 28S or 18S rDNA alignments. The strengths and weaknesses of ribosomal and Hsp90 markers, and the use of SCAR polymerase chain reaction as diagnostic tools are discussed.

Summary Punctodera mulveyi n. sp. is described and illustrated from turf grass (Poa annua) in golf course greens with other fescues in Bandon, Coos County, Oregon, USA. Females and cysts are characterised by a saccate, globose to ovoid or pear-shaped body with a protruding neck. The cuticle has a lace-like pattern of ridges and heavy punctations on the subsurface. Cysts have distinctive vulval and anal circumfenestral patterns with heavy bullae scattered around the fenestral area, these being absent in young cysts. Second-stage juveniles (J2) vermiform, tapering to a long and cylindrical tail with a bluntly rounded to occasionally clavate tail terminus. Morphologically the new species resembles all known species of Punctodera using both light microscopy and scanning electron microscopy observations, but differs from the other species either by the J2 body and stylet length, shape of head, tail and tail terminus, female and male stylet or spicule length, and in having distinctive vulval and anal circumfenestral patterns in the cysts. Molecular analysis with sequence alignments and phylogenetic trees of ITS rDNA, nuclear heat shock protein 90 and mitochondrial COI sequences separated P. mulveyi n. sp. from P. matadorensis, P. punctata, P. stonei and P. chalcoensis, but 18S and 28S were relatively conserved with a few bp differences and there were insufficient Punctodera species sequences to give strong support to a new species designation. A morphologically most closely related species, P. stonei from Canada, further supported the status of P. mulveyi n. sp. An identification key to all five nominal species of Punctodera is given.

In 2019, Cactodera milleri cysts were discovered from soil samples collected from a Chenopodium quinoa field, located in Mosca, Alamosa county, Colorado, USA. Approximately 200 lemon shaped cysts and several hundred juveniles were recovered from the affected quinoa plants. The same species was also identified from several counties in Minnesota from samples submitted over the years by the Minnesota Department of Agriculture as part of the Animal and Plant Health Inspection Service (APHIS) efforts to survey states for the presence of Pale Potato Cyst Nematode. The cysts and juveniles (J2) were recovered from soil samples through sieving and Baermann funnel extraction. The nematode species was identified by both morphological and molecular means as Cactodera milleri (Graney and Bird, 1990). To our knowledge this represents the first report of Cactodera milleri from Colorado and Minnesota.