A McLauchlan

Abundance and polymorphism of microsatellite markers in the tea tree (Melaleuca alternifolia, Myrtaceae)

Abstract The sequencing of 831 clones from an enriched microsatellite library of Melaleuca alternifolia (Myrtaceae) yielded 715 inserts containing repeat motifs. The majority of these (98%) were dinucleotide repeats or trinucleotide repeats averaging 22 and 8 repeat motifs respectively. The AG/GA motif was the most common, accounting for 43% of all microsatellites. From a total of 139 primer pairs designed, 102 produced markers within the expected size range. The majority of these (93) were polymorphic. Primer pairs were tested on five selected M. alternifolia genotypes. Loci based on dinucleotide repeats detected on average a greater number of alleles (4.2) than those based on trinucleotide repeats (2.9). The loci described will provide a large pool of polymorphisms useful for population studies, genetic mapping, and possibly application in other Myrtaceae.

Development of robust PCR-based DNA markers for each homoeo-allele of granule-bound starch synthase and their application in wheat breeding programs

The absence of expression of the granule-bound starch synthase I (GBSSI) allele from chromosome 4A of wheat is associated with improved starch quality for making Udon noodles. Several PCR-based methods for the analysis of GBSS alleles have been developed for application in wheat. A widely applied approach has involved a simple PCR followed by electrophoretic separation of DNA products on agarose gels. The PCR amplifies one band from each of the loci on chromosomes 4A (Wx-B1), 7A (Wx-A1), and 7D (Wx-D1), and the band from the Wx-B1 locus is diagnostic for the occurrence of the null Wx-B1 allele that is associated with improved starch quality. The reliable detection of the null Wx-B1 allele has been important in identifying wheat breeding lines. Allele-specific PCR has also been used to successfully detect the occurrence of the null Wx-B1 allele. In the present paper the various protocols were evaluated by testing a segregating double haploid population from a cross between Cranbrook and Halberd and the tests gave good agreement in different laboratories. The application of the DNAbased tests applied in wheat breeding programs provides one of the first examples of a molecular marker selection for a grain quality trait being successfully applied in an Australian wheat breeding program.

Interspecific amplification of tea tree (Melaleuca alternifolia-Myrtaceae) microsatellite loci-potential implications for conservation studies

This study investigated the interspecific amplification of 35 microsatellite loci developed for M. alternifolia across seven other species within the Myrtaceae. All the primers used gave successful amplification of loci in at least one of the species tested. The level of success varied between species; 88.6% of primers gave amplification products for Melaleuca spp., 74.3% for Callistemon salignus, 45.7% for Eucalyptus spp. and 25.7% for Backhousia citriodora. Sequencing of a number of amplification products confirmed the presence of microsatellites in those loci. This study shows that the development of species-specific microsatellite libraries might not always be necessary. Cross-species amplification could enable the application of microsatellite technology to studies with limited resources, a feature characteristic of conservation projects.

Microsatellite analysis in cultivated hexaploid wheat and wild wheat relatives

Hexaploid bread wheat contains three genomes, A, B and D with the formula AABBDD, amounting to a very large and complex total genome. Although bread wheat, Triticum aestivum (2n = 6x = 42), is one of the most extensively studied polyploid crops, the probable evolutionary history has only recently been established by studying the various wild relatives. Studies of meiosis and the behaviour of chromosomes in interspecific hybrids during pairing revealed the evolutionary lineages of polyploid wheat species. The A genome is present in both diploid Triticum monococcum (AA) and tetraploid Triticum turgidum (AABB) wheat. Both are morphologically similar and their hybrids exhibit chromosome pairing. As T. turgidum (AABB) and T. aestivum (AABBDD) comprise one evolutionary lineage, it was subsequently concluded that T. monococcum was the A genome progenitor of polyploid wheat (Kimber and Sears, 1987). It became apparent that einkorn diploid wheat comprised two species, T. monococcum L. and Triticum urartu Thum., the latter existing only in wild form (Dvorak et al., 1993). A re-examination of the sources of the A genome of T. turgidum and T. aestivum found it to be contributed by T. urartu (Dvorak, 1988) while the A genome of the other evolutionary lineage, Triticum timopheevii (AAGG) and Triticum zhukovskyi (AAAAGG), was contributed by T. monococcum (Dvorak et al., 1993). Synthesizing a hybrid between tetraploid wheat T. turgidum and Triticum tauschii (AA) (Coss) (= Aegilops tauschii) revealed the source of the D genome,