Root-Lesion Nematodes Reduce Yield of Intolerant Wheat and Barley

Root-lesion nematodes (Pratylenchus neglectus and P. thornei) are widely distributed and substantially reduce grain yields in wheat (Triticum aestivum L.)-producing regions of the Pacific Northwest (PNW). The objective of this research was to determine if wheat and barley (Hordeum vulgare L.) cultivars differ in tolerance to these nematode species. Field experiments were conducted by comparing yields in untreated and nematicide-treated plots over 3 yr at two locations infested with either A neglectus or P. thornei. Yield improvements from nematicide application ranged from 9 to 40% for spring cereals and 6 to 17% for winter cereals. Phenotypic tolerance responses differed (P < 0.01) among 45 cultivars of spring cereals but not among 22 and 45 cultivars of winter cereals. Tolerance ratings were assigned to spring cereals. This is the first report of wheat and barley tolerances to root-lesion nematodes in North America. Variability within data sets was used to estimate that 40 and 56 comparisons (experiments x replications) would be required to assign tolerance ratings at the 95% confidence interval for spring and winter cereals, respectively. Cultivar reactions in these tests, production and economic statistics for Idaho, Oregon, and Washington, and surveys of Pratylenchus in these states were used to estimate that P. neglectus and P. thornei reduce region-wide yields as much as 5% annually, equaling 361 Gg (361,000 metric tons) valued at $51 million. It was concluded that this yield-based screening procedure was impractical for routine screening but added emphasis to the importance of these root parasites in regions with low precipitation.