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Enzyme variation detected by starch gel electrophoresis was used to investigate the genetic structure of Oryza sativa L. species. Fifteen polymorphic loci coding for 8 enzymes were surveyed among 1688 traditional rices from Asia. Multivariate analysis of the data resulted in identification of six varietal groups, with two major ones, groups I and VI, two minor ones, groups II and V, and two satellite ones, groups III and IV. Group I is found throughout tropical Asia; it encompasses most Aman rices in Bangladesh, the Tjereh rices in Indonesia and the Hsien rices in China. Group VI is found mostly in temperate regions and in high elevation areas in the tropics; it encompasses most upland rices from Southeast Asia, the Bulu rices from Indonesia and the Keng rices from China. Groups II, III, IV and V share common differences from groups I and VI which suggest an alternative evolutionary history. Groups II and V are found in the Indian subcontinent from Iran to Burma. Well-known components of these are Aus rices from Bangladesh for group II and Basmati rices from Pakistan and India for group V. Groups III and IV are restricted to some deepwater rices in Bangladesh and Northeast India. Based on analogy with other classifications, Group I might be considered as the "Indica" type and Group VI as the "Japonica" type. Such terms, however, have a depreciated meaning due to discrepancies among various classifications.

Cultivated sugarcane clones (Saccharum spp., 2n=100 to 130) are derived from complex interspecific hybridizations between the species S. officinarum and S. spontaneum. Using comparative genomic DNA in situ hybridization, we demonstrated that it is possible to distinguish the chromosomes contributed by these two species in an interspecific F1 hybrid and a cultivated clone, R570. In the interspecific F1 studied, we observed n + n transmission of the parental chromosomes instead of the peculiar 2n + n transmission usually described in such crosses. Among the chromosomes of cultivar R570 (2n = 107-115) about 10% were identified as originating from S. spontaneum and about 10% were identified as recombinant chromosomes between the two species S. officinarum and S. spontaneum. This demonstrated for the first time the occurrence of recombination between the chromosomes of these two species. The rDNA sites were located by in situ hybridization in these two species and the cultivar R570. This supported different basic chromosome numbers and chromosome structural differences between the two species and provided a first bridge between physical and genetical mapping in sugarcane.

Vast germplasm collections are accessible but their use for crop improvement is limited-efficiently accessing genetic diversity is still a challenge. Molecular markers have clarified the structure of genetic diversity in a broad range of crops. Recent developments have made whole-genome surveys and gene-targeted surveys possible, shedding light on population dynamics and on the impact of selection during domestication. Thanks to this new precision, germplasm description has gained analytical power for resolving the genetic basis of trait variation and adaptation in crops such as major cereals, chickpea, grapevine, cacao, or banana. The challenge now is to finely characterize all the facets of plant behavior in carefully chosen materials. We suggest broadening the use of 'core reference sets' so as to facilitate material sharing within the scientific community.

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