BackgroundBoth sorghum (Sorghum bicolor) and sugarcane (Saccharum officinarum) are members of the Andropogoneae tribe in the Poaceae and are each other's closest relatives amongst cultivated plants. Both are relatively recent domesticates and comparatively little of the genetic potential of these taxa and their wild relatives has been captured by breeding programmes to date. This review assesses the genetic gains made by plant breeders since domestication and the progress in the characterization of genetic resources and their utilization in crop improvement for these two related species.Genetic ResourcesThe genome of sorghum has recently been sequenced providing a great boost to our knowledge of the evolution of grass genomes and the wealth of diversity within S. bicolor taxa. Molecular analysis of the Sorghum genus has identified close relatives of S. bicolor with novel traits, endosperm structure and composition that may be used to expand the cultivated gene pool. Mutant populations (including TILLING populations) provide a useful addition to genetic resources for this species. Sugarcane is a complex polyploid with a large and variable number of copies of each gene. The wild relatives of sugarcane represent a reservoir of genetic diversity for use in sugarcane improvement. Techniques for quantitative molecular analysis of gene or allele copy number in this genetically complex crop have been developed. SNP discovery and mapping in sugarcane has been advanced by the development of high-throughput techniques for ecoTILLING in sugarcane. Genetic linkage maps of the sugarcane genome are being improved for use in breeding selection. The improvement of both sorghum and sugarcane will be accelerated by the incorporation of more diverse germplasm into the domesticated gene pools using molecular tools and the improved knowledge of these genomes.

The DNA sequence phylogeny splits Sorghum into two lineages, one comprising the 2n = 10 species with large genomes and their polyploid relatives, and the other with the 2n = 20, 40 species with relatively small genomes. An apparent phylogenetic reduction in genome size has occurred in the 2n = 10 lineage. Genome size evolution in the genus Sorghum apparently did not involve a 'one way ticket to genomic obesity' as has been proposed for the grasses.

The cultivated Gossypium spp. (cotton) represents the single most important, natural fiber crop in the world. In addition to its fiber, the oil and protein portion of the cottonseed also represents significant economic value. To protect the worldwide economic value of cotton fiber and cotton byproducts, coordinated efforts to collect and maintain cotton genetic resources have increased over the last 100 yr. The classified genetic resources of cotton are extensive and include five tetraploid species in the primary gene pool, 20 diploid species in the secondary gene pool, and 25 diploid species in the tertiary gene pool. This report provides information on the status and contents of eight major cotton germplasm collections present across the world. Based on the findings of this report, a number of classified Gossypium species are not maintained in these collections, and several are underrepresented and vulnerable to extinction. This report presents several critical challenges and opportunities facing international efforts to enhance and preserve the world's Gossypium genetic resources. Multinational communication and collaboration are essential to protect, secure, and evaluate the global cotton germplasm resources. Without global, collaborative efforts, the rarest and most unique cotton germplasm resources are vulnerable to extinction.

Australian Oryza are an understudied and underexploited genetic resource for rice improvement. Four species are indigenous: Oryza rufipogon, Oryza meridionalis, Oryza australiensis are widespread across northern Australia, whereas Oryza officinalis is known from two localities only. Molecular analysis of these wild populations is required to better define the distinctness of the taxa and the extent of any gene flow between them and rice. Limited collections of these wild populations are held in seed and DNA banks. These species have potential for domestication in some cases but also have many traits of potential value in the improvement of domesticated rice. Stress tolerance (biotic and abiotic) and grain quality characteristics in these populations may be useful.

sists of seven Asian, Australian, and central American species (Lazarides et al., 1991). Ten species that occur in Sorghum [Sorghum bicolor (L.) Moench] breeders have long recnorthern Australia comprise the Stiposorghum section ognized the importance of exotic germplasm and noncultivated sorghum races as sources of valuable genes for genetic improvement. The (Lazarides et al., 1991). genus Sorghum consists of 25 species classified as five sections: Eu-Sorghum breeders have long recognized the imporsorghum, Chaetosorghum, Heterosorghum, Para-sorghum, and Stipotance of exotic germplasm (Duncan et al., 1991). Nonsorghum. Species outside the Eu-sorghum section are sources of imporcultivated sorghum races have been extensively used as tant genes for sorghum improvement, including those for insect and sources of genes for sorghum improvement (Rosenow disease resistance, but these have not been used because of the failure and Dahlberg, 2000). However, no species outside the of these species to cross with sorghum. An understanding of the bioeu-sorghum section have been utilized because of strong logical nature of the incompatibility system(s) that prevent hybridizareproductive barriers (Garber, 1950; Schertz and Dalton, tion and/or seed development is necessary for the successful hybridi-1980; Doggett, 1988). Resistance to major insects and diszation and introgression between sorghum and divergent Sorghum eases, for example, midge [Stenodiplosis (Contarinia) sorspecies. The objectives of this study were to determine the reason(s) for reproductive isolation between Sorghum species. The current study ghicola (Coquillett)] and downy mildew [caused by Peutilized 14 alien Sorghum species and established that pollen-pistil ronosclerospora sorghi (Weston and Uppal) Shaw], that incompatibilities are the primary reasons that hybrids with sorghum attack sorghum has been found in species of the Chaetoare not obtained. The alien pollen tubes showed major inhibition of sorghum, Heterosorghum, Para-sorghum, and Stiposorgrowth in sorghum pistils and seldom grew beyond the stigma. Pollen ghum sections (Franzmann and Hardy, 1996; Sharma tubes of only three species grew into the ovary of sorghum. Fertiliza-

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