Root-lesion Nematodes (Pratylenchus neglectus and P. thornei)

pruning of roots by root-lesion nematode Pratylenchus thornei

wheat root pruning by complex of Rhizoctonia, Pythium, and Pratylenchus

Pruning of wheat root by RLN
root pruning

One wheat variety, root-lesion nematodes controlled only in rows on left
single wheat variety with and without nematicide

Root-lesion nematodes in root cells
root-lesion nematodes inside wheat root are visible only if stained

stained root-lesion nematode inside wheat root

stained endoparasitic nematodes in wheat root

Genetic Resistance to Lesion Nematode

Lesion nematodes ( Pratylenchus neglectus and P. thornei ) occur in high numbers in many non-irrigated fields of the Pacific Northwest. 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 potentially damaging high populations occurred in at least one or more fields in 22 of the 23 counties. It is estimated that lesion nematodes reduce annual farm gate receipts from wheat sales by about $51 million in the Pacific Northwest. 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., and J.M. Nicol. 2009. Nematodes which challenge global wheat production. p. 171-187 in Wheat Science and Trade. B.F. Carver (ed.). Wiley-Blackwell, Ames, IA. (personal draft version)
Smiley, R.W., and S. Machado. 2009. Pratylenchus neglectus reduces yield of winter wheat in dryland cropping systems. Plant Disease 93:263-271. (abstract)
Smiley, R.W. 2009. Root-lesion nematodes reduce yield of intolerant wheat and barley. Agronomy Journal 101:1322-1335. (abstract)
Yan, G., R.W. Smiley, P.A. Okubara, A. Skantar, 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 92:1480-1487. (abstract)
Smiley, R.W., J.G. Sheedy, and S.A. Easley. 2008. Vertical distribution of Pratylenchus spp. in silt loam soil of Pacific Northwest dryland crops. Plant Disease 92:1662-1668.(abstract)
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)
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.

Reports of individual tests:

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:N007.
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:N015.
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:N016.
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:N012.
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:N011.
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:N014.
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:N013.
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:N010.
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:N009.
Sheedy, J.G., R.W. Smiley, P.M. Hayes, A.L. Thompson, S.A. Easley, and A.E. Corey. 2008. Resistance to root-lesion nematode of barley entries in the Coordinated Agricultural Project, 2007; Pratylenchus thornei. Plant Disease Management Reports 2:N037.
Sheedy, J.G., W.J. Raupp, A.L. Thompson, and R.W. Smiley. 2008. Resistance to root lesion nematodes of Chinese Spring x Aegilops speltoides addition lines, 2007; Pratylenchus neglectus and P. thornei. Plant Disease Management Reports 2:N038.
Thompson, A.L., J.G. Sheedy, K.G. Campbell, P.A. Okubara, and R.W. Smiley. 2008. Resistance of wheat to the root lesion nematode; Pratylenchus thornei, 2008. Plant Disease Management Reports 2:N039.