Development and Use of Nematode-Resistant Varieties

Rev 05/07/15

Definitions: 

Note the effect of vertical resistance on selection for aggressiveness on potatoes in Europe, tobacco in NC, soybean cyst nematode in the southeastern US. Will this happen with the Mi gene in tomato?
Consider the potential for stabilizing selection and management of population gene frequencies since genes for aggressiveness may not confer advantage in absence of selection pressure.

This is an important area in pest and nematode management.
- How is the resistance expressed relative to the nematodes?

Availability of Resistance 

  
Specialization Host Range Resistance
sedentary ********** ** ********
endoparasites ******** ** ******
****** **** ***
**** ****** **
migratory **** ****** **
endoparasites **** ******* **
**** ******** **
ectoparasites **** ********** **

Concept by Roberts (1982).  But how much have we looked for resistance to different types of nematodes, especially when there are no obvious signs or symptoms?
- also, how much of a problem are nematodes in each category?

Expression of Resistance:

a. Resistance to penetration
b. Resistance to development
c. Resistance to productivity (reproduction)

Mechanisms of Resistance:

A very complete understanding of resistance mechanisms is being developed through the work of  Dr. Valerie Williamson and colleagues.  They study the Mi gene which confers resistance to Meloidogyne spp. in tomato.  The gene provides resistance to Meloidogyne incognita, M. arenaria, and M. javanica.  It also confers resistance to the potato aphid, Macrosiphum euphorbiae, and the white fly Bemisia tabaci.

There are important developments in the understanding of resistance in soybeans to Heterodera glycines.

Many resdistant varieties were developed over several years by USDA scientist Dr. Hartwig.  In general, resistance in soybeans is expressed as a hypersensitive response.  Syncytia are initiated in both resistant and susceptible cultivars but degenerate in the resistant cultivars.  They become necrotic and unable to support nematode development (Huang, 1998). Some of the varieties developed by Hartwig did not yield as well as susceptible varieties in the absence of soybean cyst nematode.  Many of the sources of resistance have now been integrated into a high-yielding variety, CystX.

In 2011 and 2012, resesarchers at Southern Illinois University Carbondale and the University of Missouri at Columbia identified and validated the gene at the Rhg4 (for resistance to Heterodera glycines 4) locus.   The Rhg4 gene encodes a serine hydroxymethyltransferase (SHMT). The enzyme catalyzes conversions between serine and glycine and is essential for cellular carbon metabolism. Alleles of Rhg4 conferring resistance or susceptibility differ by two genetic polymorphisms that alter a key regulatory property of the enzyme. (Liu et al., 2012).

 

 

References:

Roberts, P.A.  1982.  Plant resistance in nematode pest management.  Journal of Nematology 14:24-33.

Kaplan, D.T. and E.L. Davis 1987.  Mechanisms of pant incompatibility with nematodes.  Pp 267-276 in: J.A. Veech and D.W. Dickson (eds).  Vistas on Nematology.  E.O Painter, Florida.

Huang, J.S. 1998.  Mechanisms of resistance. Pp353-368 in Sharma, S.B. (ed). The Cyst Nematodes. Kluwer, Dordrecht.

Liu, S., Kandoth, P.K., Warren, S.D., Yeckel, G., Heinz, R.,Alden, J., Yang, C., Jamai, A., El-Mellouki, T.,. Juvale, P.S., Hill, J., Baum, T.J., Cianzio, S., Whitham, S.A., Korkin, D., Mitchum, M.G.,Meksem, K. 2012. A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens. Nature doi:10.1038/nature11651.


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