1.1.18
MARKERS FOR DISEASE RESISTANCE: A TARGETED APPROACH

AT MITCHELL1, DL WHISSON2, PJ MURPHY1 and AC McKAY2

1Department of Crop Protection, University of Adelaide, Waite Campus, Glen Osmond, SA 5064, Australia; 2S.A. Research and Development Institute (SARDI), Waite Precinct, GPO Box 397, Adelaide, SA 5001, Australia

Background and objectives
The nematode Anguina funesta is a mechanical vector for Clavibacter toxicus, the bacterium that produces a toxin causing annual ryegrass toxicity (ARGT). ARGT occurs in South Australia and Western Australia, and results in stock losses when sufficient amounts of infected seed heads are ingested by grazing animals [1]. Nematode resistance is thought to be mediated by two dominant genes in the ARGT-resistant ryegrass, Lolium rigidum, cv. Guard.

The targeted approach to obtain molecular markers for nematode resistance involves the cloning of ryegrass-resistance gene analogues (RGAs). Resistance genes and RGAs have been found to form multiple clusters in the genomes of many plant species [2]. This feature makes RGAs ideal markers of resistance-gene clusters in the poorly characterized L. rigidum genome. Once ryegrass RGAs are obtained they can then be tested for association with nematode resistance.

Results and conclusions
Analogues of resistance genes N for TMV resistance in tobacco and L6 for flax rust resistance were cloned from ryegrass. These ryegrass RGAs were used as molecular markers and screened against nematode-resistant and susceptible ryegrass lines. RGAs associated with A. funesta resistance in L. rigidum are in the process of being identified.

References
1. McKay AC, Ophel KM, 1993. Annual Review of Phytopathology 31, 151-157.
2. Kanazin V, Marek LF, Shoemaker RC, 1996. Proceedings of the National Academy of Sciences, USA 93, 11746-11750.