Genomics and breeding of Brassicaceae crops

crops include oil crops, vegetables, condi-ments, fodder crops, and ornamental plants. Most of these crops belong to or are closely related to the genus Brassica. The Brassicaceae also includes the most intensively studied model plant, Arabidopsis thaliana. In molecular genetic studies of Brassicaceae crops, information on A. thaliana genes is highly useful, and many genes important for plant breeding have been identified. Different species of Brassica have various numbers of chromosomes. The genome relationship of three monog-enomic species and three digenomic species that are well known as U's triangle was discovered in Japan, and relationships between different genera have also been studied (Mizushima 1980). In these studies, interspecific and inter-generic hybridizations have been performed, and some in-terspecific and intergeneric hybrids have been used as breeding materials. Studies on interspecific and intergeneric hybridization are reviewed by Kaneko and Bang in this special issue. Genome synteny relationships between different species in Brassica and closely related genera are complicated, as exemplified by the different numbers of chromosomes between species. The monogenomic species of Brassica and closely related genera have three copies, on average, of genes homologous to each A. thaliana gene, indicating whole genome triplication in the evolution of the ancestral species of Brassica and closely related genera. The recent development of next-generation sequencers has accelerated the determination of whole genome sequences from many species. A draft sequence of the Brassica rapa genome was published in 2011 (Wang et al. 2011), and whole genome sequences of other species of Brassicaceae crops will also be published soon. The progress with genome studies of Brassicaceae crops and genome relationships between them are described by Ashutosh et al. Many Brassicaceae crops have self-incompatibility, which is not common in other seed-propagated crops. Self-incompatibility is a commonly found trait in many angiosperm species, but self-compatible plants have been selected as crops. The genetics and molecular mechanisms of self-incompatibility have been most intensively studied using Brassica species, and this trait is also used as a tool for producing F 1 hybrid seeds of Brassicaceae vegetables. Recent studies on Brassica self-incompatibility are introduced by Kitashiba and Nasrallah. On the other hand, the trait most widely used for F 1 hybrid seed production in many crop species is cytoplasmic male sterility. Cytoplas-mic male-sterile lines can be obtained by interspecific hy-bridization and repeated backcrossing with a paternal species , and this form of sterility is considered to be caused by incompatibility between …