Summary — Lucerne (Medicago sativa) is a major perennial forage legume and includes two main sub-species. The variation available within a group of 26 tetraploid populations of this complex was investigated with random amplified polymorphic DNA (RAPD) markers. Thirty seedlings per population were analysed. Twenty-nine reproducible markers, 24 being polymorphic, were obtained with four primers. The variation partitioning was studied using the AMOVA technique. The genetic variation proved to be nearly equally distributed within and between populations. The between-population variation was further partitioned between groups (falcata, Flemish, mediterranean) and between populations within groups. The latter source of variation was the major one. Although this study included a sub-species level, the within-population variation was very large probably due to the outcrossing reproduction and the tetraploidy. A similar approach was used to distinguish varieties and proved to be very efficient. The within-population dissimilarity indices were very variable according to the populations; the falcata and Flemish-type materials showed on average a larger within-population dissimilarity. The between-population dissimilarities were calculated and a dendrogram was drawn. This made it possible to separate the populations belonging to the two sub-species and the populations of subspecies sativa largely introgressed by falcata. The relationships among the sativa populations partly fitted with the known origin of the material or with their agronomic behaviour.Medicago sativa = lucerne / RAPD marker / variation pattern

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Reciprocal crosses were performed between Brassica napus (AACC, 2n = 38) cv. Brutor and Sinapis alba (SalSal, 2n = 24) cv. Carine. Using fertilized ovary culture, 2.2 and 1.9% of interspecific hybrids were produced when white mustard was the female and the male parent, respectively. On S. alba cytoplasm, three plants with a BC1-like structure (SalSalAC, 2n = 43) were obtained and ACSal (2n = 31) and AACCSal (2n = 50) hybrids on reciprocal crosses. At the same ploidy level, no differences in meiotic behavior were observed. The amphidiploids (AACCSalSal, 2n = 62), produced after colchicine treatment of ACSal hybrids, were compared with the somatic hybrids previously obtained from the same parental varieties. Only two somatic hybrids differed and one of them lost Idh-2 rapeseed isozymes, whereas all the plants presented an hybrid pattern for all the other molecular markers. The plants with 50 chromosomes (AACCSal) from sexual hybrids were similar whatever their origins. Their comparison with back-cross progeny of somatic hybrids revealed that the latter one differed either by chromosome number, ranging from 42 to 54, or by the percentage of cells with less than 12 univalents and with multivalents. From our results, the efficiency of protoplast fusion compared with sexual crosses as a tool to introduce new traits in a crop is discussed.

A "F1" diploid population between Solanum tuberosum 2 x and the wild Solanum spegazzinii was studied. It segregated for resistance against the potato cyst nematode Globodera pallida derived from the wild species. The inheritance had a quantitative nature. Linkage maps of AFLP and RFLP markers were constructed for both parents. Three QTLs were identified on the map of the resistant parent on chromosomes V, VI and XII, respectively. The first one had a major effect and explained more than 50% of the total variance of resistance. It is located in a cluster of resistance genes and may be the same locus as Gpa which has been described formerly. The two others explained about 20% of the total variance each. The QTL on chromosome XII is also in a cluster of resistance genes, and in an orthologous position with resistance genes against nematodes in tomato and pepper.

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