Distribution, virulence and genetic management of root lesionnematodes in the Pacific Northwest USA

Root lesion nematodes (RLNs) have been identified in more than 90% of dryland cropping fields in the Pacific Northwest (PNW; Oregon, Washington, Idaho) USA. Pratylenchus neglectus dominates but P. thornei and mixtures of both species occur commonly. Until recently, RLNs were only considered to cause significant yield loss in annual spring crops with traditional winter wheat-summer fallow rotations considered unsuitable for damaging RLN populations to develop. Recent research has shown that spring wheat and barley yields increased up to 98% and 15% respectively in response to aldicarb (4.2 kg a.i./ha) applied at planting in P. neglectus infested soil and 49% and 14% respectively in P. thornei infested soil. Yields of winter wheat and barley cultivars grown at the same locations also responded up to 21% and 27% respectively in P. neglectus infested soil and 15% and 20% respectively in P. thornei infested soil. Glasshouse resistance screening showed that all tested PNW wheat cultivars were susceptible to both RLNs. Barley cultivars were generally more resistant than wheat cultivars but still moderately susceptible to P. neglectus and moderately resistant to moderately susceptible to P. thornei. Crop species identified as resistant to P. neglectus and/or P. thornei and suitable for crop rotation are either not well adapted to PNW cropping systems or have marginal economic viability. Breeding cereal cultivars with tolerance and resistance to RLNs has proven an effective management strategy in similar international situations and has been undertaken collaboratively in the PNW. Characterisation of commercial cultivars and advanced breeding lines for tolerance and resistance has begun as has the introduction of elite sources of tolerance and resistance genes through a targeted crossing program. Molecular techniques are also being developed to identify RLNs to species from soil samples and resistance gene markers to assist breeding selection.