An assessment of nematodes affecting wheat in Montana
Al-Khafaji, Riyadh Talib
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Nematodes represent a major biological constraint on wheat and barley production worldwide, and yet no comprehensive assessment of plant parasitic nematodes associated with cereals has been conducted for Montana. To address this shortcoming, a survey was conducted to determine the species of plant parasitic nematodes associated with small grains, and an assessment of variation in virulence across 4 crops and 8 resistant wheat lines was conducted for Pratylenchus neglectus populations collected from across Montana. The survey, conducted across 11 counties, and found widespread distribution of P. neglectus, Tylenchorhynchus spp., and Tylenchus spp. within the state. Populations of P. neglectus were generally low (268 to 363 nematodes/kg of dry soil for 2015 and 2016, respectively). However, destructive populations were detected in 9 fields in both 2015 and 2016. In addition, populations of the cereal cyst nematode Heterodera avenae were detected. Cereal cyst nematode Heterodera filipjevi, a regulated pest, was detected in only one field. Additional species of parasitic nematode were detected, but rare. To assess the applicability of resistant crops and wheat lines for management of P. neglectus, greenhouse trials were conducted using nematode populations from within the state. In two trials conducted with resistant crops, significant interaction was detected between crops and populations of nematodes (ANOVA P< 0.001 and P= 0.01). In the first trial, populations from 3 counties were virulent on barley (mean reproductive factor = 10.9). Populations from other counties were either non-virulent on barley, or their inoculations were ineffective. In the second trial, 2 of the 3 populations were again virulent on barley (mean Rf = 4.4 and Rf = 10.7). Trials examining virulence across resistant wheat lines found no interactions between populations and wheat lines (ANOVA P= 0.60 and P= 0.93). While significant variation in reactions to the resistant lines were detected, none of the lines appeared particularly resistant to Montana populations, with mean Rf values of 13.1 and 15.4 for trials 1 and trials 2, respectively. Results suggest plant parasitic nematodes are localized problems, with P. neglectus and Heterodera species of particular concern, and that "resistant" wheat lines and barley may ineffective in managing P. neglectus in some regions of the state.