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Genetic
Resistance to Lesion Nematode
Lesion
nematodes ( Pratylenchus neglectus and P. thornei
) occur in high numbers in many fields cropped annually.
Two surveys covering 232 wheat fields in 23 counties of Idaho, Oregon and Washington showed that one or both species were present 95% of fields sampled, and that populations exceeded the economic threshold limit (2,000/kg soil) in at least one or more fields in 22 of the 23 counties. Tillage does not appear to increase or reduce numbers of lesion
nematodes. Most crop species are susceptible, including most
small grain cereals, food and forage legumes, and brassica crops.
Yields of susceptible spring wheat varieties have been reduced
as much as 70%, with little or no visual symptoms expressed
in the crop canopy other than a generally unthrifty appearance.
Current emphasis is on identifying sources of genetic resistance
in wheat, in collaboration with wheat breeding programs in Oregon
and Washington, and international programs in Australia, Syria
(ICARDA) and Turkey (CIMMYT). Field tests have shown that 90 locally adapted varieties and advanced breeding lines exhibit a wide range of tolerance levels to both P. neglectus and P. thornei. Several varieties are tolerant to both species. Barley is generally more tolerant and resistant than wheat although considerable variation occurs among barley varieties and breeding lines. These findings indicate that growers can significantly improve wheat production efficiency by growing tolerant rather than intolerant varieties on highly infested soils. However, all Pacific Northwest varieties and breeding lines also were shown to be good hosts allowing high levels of reproduction of these nematodes. Barley and safflower reduced populations of Pratylenchus. Brassica and chickpea crops supported high rates of P. neglectus reproduction and led to high populations that posed increased risk to production of intolerant wheat varieties. Crosses have been made to introgress resistance genes into six commercial wheat varieties and advanced breeding lines, with the expectation that even greater efficiencies will be attained with varieties that are both resistant and tolerant to both species of this nematode. Representative papers include
the following.
- Smiley,
R.W., K. Merrifield, L.-M. Patterson, R.G. Whittaker, J.A.
Gourlie, and S.A. Easley. 2004. Nematodes in dryland field
crops in the semiarid Pacific Northwest USA. Journal of
Nematology 36:54-68. (abstract)
- Smiley,
R.W., J.A. Gourlie, R.G. Whittaker, S.A. Easley, and K.K.
Kidwell. 2004. Economic impact of Hessian fly (Diptera:
Cecidomyiidae) on spring wheat in Oregon and additive yield
losses with Fusarium crown rot and lesion nematode. Journal
of Economic Entomology 97:397-408. (abstract)
- Smiley,
R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2004.
Australian technology used to demonstrate lesion nematode
damage in Pacific Northwest (USA) wheat. p. 218-219 In.
K. Ophel-Keller (ed.). Proceedings of the Third Australasian
Soilborne Diseases Symposium.
- Smiley,
R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2005.
Pratylenchus thornei is associated with reduced
wheat yield in Oregon. J. Nematol. 37:45-54.
(abstract)
- Smiley,
R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2005.
Suppression of wheat growth and yield by Pratylenchus
neglectus in the Pacific Northwest. Plant Disease 89:
958-968.
(abstract)
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Sheedy, J.G., R.W. Smiley, and S.A. Easley. 2008. Vertical distribution of Pratylenchus species in soils of wheat-based dryland cropping systems. Plant Dis. 92:xxx-xxx. (provisionally accepted, pending review).
- Yan, G., R.W. Smiley, P.A. Okubara, S.A. Easley, J.G. Sheedy, and A.L. Thompson. 2008. Detection and discrimination of Pratylenchus neglectus and P. thornei in DNA extracts from soil. Plant Disease 92: (prepared for submission).
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Sheedy, J.G., R.W. Smiley, S.A. Easley, and A.L. Thompson. 2008. Resistance of Pacific Northwest spring wheat and barley cultivars to root-lesion nematode, 2007; Pratylenchus thornei. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Smiley, S.A. Easley, and A.L. Thompson. 2008. Root-lesion nematode resistance ratings of Pacific Northwest winter wheat and barley cultivars, 2007; Pratylenchus thornei. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Smiley, S.A. Easley, and A.L. Thompson. 2008. Resistance of Pacific Northwest winter wheat and barley cultivars to root-lesion nematode, 2007; Pratylenchus neglectus. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Smiley, A.L. Thompson, and S.A. Easley. 2008. Tolerance of Pacific Northwest spring wheat and barley cultivars to root-lesion nematode, 2006; Pratylenchus neglectus. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Smiley, A.L. Thompson, and S.A. Easley. 2008. Tolerance of Pacific Northwest spring wheat and barley cultivars to root-lesion nematode, 2007; Pratylenchus neglectus. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Smiley, S.A. Easley, and A.L. Thompson. 2008. Tolerance of Pacific Northwest winter wheat and barley cultivars to root-lesion nematode, 2006; Pratylenchus neglectus. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Smiley, S.A. Easley, and A.L. Thompson. 2008. Tolerance of Pacific Northwest winter wheat and barley cultivars to root-lesion nematode, 2007; Pratylenchus neglectus. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Smiley, A.L. Thompson, and S.A. Easley. 2008. Root-lesion nematode tolerance reaction of Pacific Northwest spring wheat and barley cultivars, 2007; Pratylenchus thornei. Plant Disease Management Reports 2:xxxx. (in press).
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Sheedy, J.G., R.W. Sheedy, J.G., R.W. Smiley, A.L. Thompson, and S.A. Easley. 2008. Spring wheat cultivars response to aldicarb in soil infested by root-lesion nematodes, 2007. Plant Disease Management Reports 2:xxxx. (in press).
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