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Wheat Information Service
Number 90:21-30 (2000)
Research article

Intraspecific genetic diversity for resistance to 'Wheat rusts in wild Triticum and Aegilops species

Harjit-Singh and H. S. Dhaliwal

Department of Biotechnology, Punjab Agricultural University, Ludhiana. 141004, India


Summary

Intraspecific variability for resistance to leaf rust (Puccinia recondita f. sp. tritici) and stripe rust (P. striiformis) was studied in four wild Triticum and nine Aegilops species to assess their potential as reservoir of novel sources of resistance. Multipathotype seedling tests of wild Triticum and Aegilops species with individual P. recondita and P. striiformis pathotypes showed significantly large intraspecific diversity for rust resistance. A number of reaction patterns were observed among the limited number of accessions tested for each of the species. Segregation for rust reaction to individual pathotypes of rusts in F₂ generations of 31 intraspecific crosses in wild Triticum and Aegilops species further confirmed the genetic diversity for rust resistance within these species. Of nine crosses among five accessions of Aegilops triuncialis, eight crosses gave a 15:1 segregation ratio of resistant: susceptible F₂ plants indicating at least four different dominant resistance genes within the five accessions. Similar data were obtained from intraspecific crosses in other species, even when the accessions of a species studied were collected from the same site. These observations have important implications in designing strategies for utilizing wild species, as donors of disease resistance in wheat.
Key words: Aegilops, Triticum, Diversity, Rust, Resistance


Introduction

Wild relatives of wheat provide a rich reservoir of genes for resistance to various wheat diseases (Sharma and Gill 1983; Jiang et al. 1994; Friebe et al. 1996; Harjit-Singh et al. 1998). Resistance to all the three wheat rusts, viz. leaf rust (Puccinia recondita f. sp. tritici), stripe rust (P. striiformis) and stem. rust (P. graminis tritici) has been transferred from wild Triticum and Aegilops species (McIntosh 1998). Many of the alien rust resistance genes transferred into cultivated wheat and deployed have been overcome.

The transfer and exploitation of an alien gene for resistance to a particular disease from a donor species often precludes its utilization as a source for other genes. However, the same species may have additional intraspecific diversity for resistance and could be a useful potential donor for more resistance genes for the same disease. Therefore, before looking for new sources for resistance genes in other species, it would be desirable to study intraspecific diversity for resistance in the same species for future use.

The present study was conducted to assess the extent of intraspecific diversity for rust resistance in four wild Triticum and nine Aegilops species using Indian leaf rust and stripe rust isolates with diverse avirulence/virulence on leaf rust (Lr) and stripe rust (Yr) resistance genes, respectively. All the species investigated revealed large intraspecific variability for rust resistance for their continuous exploitation for resistance breeding.

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