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The development of cultivars resistant to cereal cyst nematode (CCN) is a primary objective in wheat breeding in the southern wheatbelt of Australia. Nine CCN resistance genes have been identified in wheat and its relatives, some of which confer resistance to the Australian pathotype of CCN (Ha13). Cultivars released in Australia with CCN resistance carry either the Cre1 or CreF gene, with the Cre3 gene present in advanced breeding lines. The biological assay for CCN resistance screening in wheat is time-consuming, not reliable on a single-plant basis, and prone to inconsistencies, thus reducing the efficiency of selection amongst breeding lines. Using gene sequences initially isolated from the Cre3 locus, a DNA-based marker selection system was developed and applied to unambiguously identify wheat lines carrying resistance alleles at theCre1 and/or Cre3 loci in breeding populations derived from diverse genetic backgrounds. Homologues of sequences from the Cre3 locus, located elsewhere in the wheat genome, can also be used to select wheat lines with a newly identified CCN resistance gene (Cre6) introgressed from Aegilops ventricosa. Application of these markers has become an integral part of the southern Australian breeding programs.

Hybridization of Hordeum vulgare L. (2n = 14) with H. bulbosum L. (2n = 14) results in a high frequency of haploids of H. vulgare through selective elimination of H. bulbosum chromosomes. Doubled haploids were produced by nitrous oxide (N2O) or 0.1% colchicine with and without dimethyl sulfoxide (DMSO) treatments. Pollinated florets (vulgare × bulbosum) were treated with N2O under 21.1 × 10−3 to 42.2 × 10−3 kg/m2 pressure (30 to 60 psi) and the frequency of doubled haploids ranged from 0 to 100%, depending upon pressure and duration of exposure. However, the frequency of seedlings from the most effective N2O doubling treatment was very low (0.5%) whereas 17% of the florets pollinated in the controls resulted in seedlings. Of the haploid seedlings treated with either 0.1% colchicine or colchicine plus DMSO, doubled sectors occurred in 37.4 and 55.8% respectively. Seed was also obtained from 3% of the untreated plants indicating a low frequency of natural chromosome doubling. The proportion of doubled tillers per plant was 61.6% in colchicine plus DMSO treatments and 30.8% in the colchicine treatments. Colchicine plus DMSO was the most efficient treatment for doubling barley haploids during early stages of development.

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Meiotic pairing was studied in the following species and their haploid derivatives: Hordeum cordobense 2x, H. marinum 2x and 4x, H. secalinum 4x, H. capense 4x, H. jubatum 4x, H. brachyantherum 4x and 6x, H. lechleri 6x, and H. procerum 6x. The study revealed (i) homologous pairing in diploid species and very little nonhomologous associations in their mono-haploids; (ii) the alloploid nature of the polyploid taxa; (iii) a certain degree of homoeologous pairing in polyhaploids despite the diploid-like meiotic behaviour of the polyploids; (iv) genetic variation in the suppression of homoeologous chromosome pairing in different Hordeum species.Key words: Hordeum, meiotic pairing, haploids.