Discovery and distribution of root lesion nematode, Pratylenchus neglectus, in Montana
Johnson, Wendy Ann.
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Root lesion nematodes (Pratylenchus neglectus and P. thornei) cause significant yield losses for wheat worldwide. To assess the prevalence of root lesion nematodes in Montana, soil samples were collected statewide in 2006 and 2007. In 2006, P. neglectus was found in 12 of the 17 counties and in 41% of all field samples surveyed. In 2007, P. neglectus was found in 11 of 15 counties and in 37% of all field samples surveyed. No P. thornei was found. For fields having root lesion nematode in 2006, P. neglectus mean population densities were 1213 nematodes/kg soil with population densities exceeding the damage threshold of 2500 nematodes/kg soil in 14% of the sampled fields. For fields having root lesion nematodes in 2007, P. neglectus mean population densities were 1303 nematodes/kg dry soil with densities exceeding the damage threshold of 2500 nematodes/kg dry soil in 13% of the samples. Damaging populations were restricted to the north central part of the state and were generally found in fields following a crop of winter wheat (p= 0.02). Stunt nematodes (Tylenchorynchus spp.) were detected in 93% and 85% of sampled fields for 2006 and 2007, respectively.New sources of tolerance and resistance to root lesion nematode are highly sought after due to limited breeding materials. Resistances of 16 cultivars were evaluated through inoculated greenhouse trials where multiplication of the pathogen was observed after 12 weeks of growth. No significant differences in multiplication factors (Rf= population final/population initial) were observed for the first trial (F test, p=0.11) though significant differences were evident between cultivars in the second trial (F test, p<0.001). From the greenhouse trials, the historic cultivar, Ceres was identified as a potentially useful source of nematode resistance. Tolerance evaluations were conducted at two nematode-infested sites (Ulm and Bozeman, MT) where the yield responses of 20 cultivars, with and without nematicide (Temik 15G tm) treatment, were compared. On average, nematicide treatments reduced yields at both sites (Ulm = 0.4% and Bozeman = 7.3%). No significant differences in nematode tolerances was detected among cultivars (Ulm, p=0.08; Bozeman, p=0.14).