Generación e instalación del par de claves

The use of MAS has been advocated as a highly efficient alternative to bioassays because it offers rapid and precise selection of the target gene (Tanksley et al. 1989), without the need to wait for phenotypic expression (Peng et al. 1999). MAS can

produce reliable results on a single-plant basis and obviates the confounding effects of environment on phenotyping or biological assays.

Previous studies have reported the identification and mapping of CCN resistance genes, Cre1 in Triticum aestivum on 2B (de Majnik et al. 2003), Cre2 in Ae. ventricosa on 5Nv) (Delibes et al. 1993, Ogbonnaya et al. 2001a), Cre3 from Ae. tauschii on 2D, (Eastwood et al. 1994, Ogbonnaya et al. 2001b), Cre4 in Ae. tauschii (Eastwood et al. 1991), Cre5 from Ae. ventricosa on 2A, (Jahier et al. 2001), Cre6 (Ae. ventricosa 5Nv) (Jahier et al. 1996, Ogbonnaya et al. 2001a), Cre7 in Aegilops truincialis (Romero et al. 1998) and Cre8 in T. aestivum on 6B (Williams et al. 2003). CreX and CreY identified in Ae. variabilis accession no. 1 confers resistance against the pathotype Ha12.
The effective implementation of molecular markers linked to CCN resistance relies on the diagnostic ability of the marker(s), user-friendly protocols and their utility across diverse genetic backgrounds. Such markers ensure selection of a target gene based on the presence of linked/diagnostic markers. Closely linked DNA markers that have been validated and used in MAS for CCN resistance breeding in Australia are given in Table 2. These widened the range and scope of MAS in breeding for CCN resistance in wheat. In the breeding program of Australian Grain Technologies Pty Ltd, the deployment of markers linked to CCN resistance genes is for population enrichment of complex cross including backcross and/or topcross F1 plants. They are also being

used to track the incorporation of CCN resistant genes into adapted elite lines and on early-generation breeding materials to increased the frequency of CCN resistant lines (Martin et al. 2004).

ACKNOWLEDGMENTS

The Australian organisations Grains Research and Development Corporation, Victorian Department of Primary Industries, Graingene and CSIRO Plant Industry supported this work.

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Table 2

genes be

2. Some DNA diagnosti

eing deployed by Austra

c markers linked to cereal cys alian wheat breeding programs.

st nematode resistance

Gene Chromosome location Markers Reference

Cre1 2BL M19Cre1F, M19Cre1R de Majnik et al. 2003

Cre3 2DL Cre3spF, Cre3spR Ogbonnaya et al. 2001b

gwm301, gwm577 Martin et al. 2004

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PRELIMINARY INVESTIGATION OF RESISTANCE