SCN

 

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Feeding
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Soybean Cyst Nematode Resistance:

The soybean cyst nematode (SCN), Heterodera glycines Ichinohe is a devastating pest of the soybean (Glycine max L Merr.) worldwide. Yield losses in the U.S.A. due to SCN were estimated at 213 million bushels in 1996 and 219 million bushels in 1997. This represents a loss in income to soybean farmers of approximately $1.5 billion.  This is more than the soybean loss from all other pests combined. SCN infection of soybean causes various symptoms that may include chlorosis, root necrosis, loss in seed yield and suppression of root and shoot growth. In general, nematodes cause an estimated loss of approximately $100 billion per year worldwide. 

Chemical control (soil fumigation) of SCN is not normally used because the economical and environmental costs are prohibitive. Therefore, cultural practices, such as crop rotation and the use of resistant cultivars, are used to mitigate the damage of SCN. Use of naturally occurring genes to control soybean cyst nematode and other pests is generally more acceptable ecologically and economically than chemical control. 

There are several known loci encoding resistance to SCN and specific soybean genotypes have distinct responses to particular SCN races. Soybean genotypes with different responses to SCN races serve as differentials to identify SCN races. However, the contributions of different loci to the resistance response at the molecular level is not known.  Furthermore, the functions of genes involved in resistance are unknown. 

 Image of female cyst nematodes emerging from an infected root
Figure(1): Female Cyst Nematodes emerging from an infected root.

See Nematode Basics    SCN Life Cycle    Nematode Feeding   Extracting nematodes

Microscopic view of viable and inviable cysts in infected soybean rootsInfected soybean roots in one petri dish on the left, versus uninfected roots in another petri dish on the right.

 

 

 

 

 

Figure(2): Microscopic view of viable and inviable cysts (brown) in infected soybean roots.

Figure(3): Infected soybean roots (left) vs. uninfected roots (right).

We are taking two approaches to enhancing the resistance of soybean to SCN:

1)     Cloning of resistance genes by map position; and

2)      Identifying genes involved in resistance by monitoring their expression patterns using
differential display and microarrays.

 
Selected References:

Devine, T.E., B.F. Matthews, J.M. Weisemann and H.S. Beard. 1995. Registration of recombinant inbred maplines of soybean germplasm. Probe 5:8.

Lin, J.J, J. Kuo, J. Ma, J.A. Saunders, H.S. Beard, M.H. MacDonald, W. Kenworthy, G.N. Ude and B.F. Matthews. 1996. Identification of molecular markers in soybean using RFLP, RAPD, and AFLP DNA mapping techniques. Plant Molec. Biol. Report.   14:156-169.

Ude, G, T.E. Devine, L.D. Kuykendall, B.F. Matthews, J. A. Saunders, W. Kenworthy and J.J. Lin. 1998. RFLP Report: Genetic mapping of the soybean gene Rj4, conditioning nodulation restriction with Bradyrhizobium elkanii, a chlorosis-inducing microsymbiont, with molecular marker loci. Symbiosis.   26: 101-110.

Cregan, P. J. Mudge, E.W. Fickus, L. Fredrick Marek, D. Danesh, R. Denny, R. C. Shoemaker, B.F. Matthews, K. G. Lark and N. D. Young. 1999. Targeted isolation of simple sequence repeat markers through the use of bacterial artificial chromosomes. Theor. App. Genet. 98: 919-928