Summarises the impact of trypanosomiasis on development of trypanotolerant livestock. Describes current genetic research being carried out by collaborating national and international organisations in the African Trypanotolerant Livestock Network, and discusses the importance of conserving these genetic resources to Africa.

Human chromosome (Chr) 18(HSA 18) contains approximately 85 million base pains of DNA. Thirty genes and pseudogenes have been mapped to HSA 18 by somatic cell genetics or in situ hybridization. Two bovine genes - Yamaguchi sacroma viral oncogene homology 1 (YESI) and desmocollin type 1 (DSC1) - homologous to HSA 18 loci have been mapped by in situ hybridization to chr 24, and Zoo-FISH analyses show that HSA18 loci are located entirely on BTA24. It is reported here the genomic localization of eight bovine genes homologous to HSA18 genes, ADCYAPI, CDH2, CYB5, DSC2, FECH, NDUFV2, PAI2, and TTR, using somatic cell genetics and linkage analysis in the International Bovine Reference Panel (IBRP).

Four single-strand conformation variants of the bovine tumor necrosis factor alpha gene by analysis of PCR-amplified fragments were identified. The variants are inherited in Mendelian fashion and are informative for linkage mapping. We have mapped the bovine gene to Chromosome (Chr) 23 in a panel of somatic cell hybrids and observed genetic linkage to the major histocompatibility complex (BoLA) genes and microsatellite markers on bovine Chr 23 in an internatonal bovine reference family panel. The distribution of the alleles was determined in cattle of different breeds and of different geographical origins, which included trypano-susceptible and trypano-tolerant cattle.

Plantains and bananas (Musa spp. sect. eumusa) originated from intra- and interspecific hybridization between two wild diploid species, M. acuminata Colla. and M. balbisiana Colla., which contributed the A and B genomes, respectively. Polyploidy and hybridization have given rise to a number of diploid, triploid, and tetraploid clones with different permutations of the A and B genomes. Thus, dessert and highland bananas are classified mainly as AAA, plantains are AAB, and cooking bananas are ABB. Classification of Musa into genomic groups has been based on morphological characteristics. This study aimed to identify RAPD (random amplified polymorphic DNA) markers for the A and B genomes. Eighty 10-mer Operon primers were used to amplify DNA from M. acuminata subsp. burmannicoides clone 'Calcutta 4' (AA genomes) and M. balbisiana clone 'Honduras' (BB genomes). Three primers (A17, A18, and D10) that produced unique genome-specific fragments in the two species were identified. These primers were tested in a sample of 40 genotypes representing various genome combinations. The RAPD markers were able to elucidate the genome composition of all the genotypes. The results showed that RAPD analysis can provide a quick and reliable system for genome identification in Musa that could facilitate genome characterization and manipulations in breeding lines.Key words: banana and plantain, A and B genomes, genomic groups, RAPD markers.

To optimize designs to implement marker-assisted introgression programs aiming to introgress three unlinked quantitative trait loci (QTL), the present paper studies different alternatives versus a traditional backcross or intercross phase. Four alternative backcross strategies appear to be more advantageous by having 50 percent less genotyping load than a traditional backcross strategy tracking all three QTL at a time through a single line. A multiplication phase following the selection of homozygous animals at the three QTL as an intercross alternative allows doubling of the number of homozygous animals in a mouse model compared with the first intercross generation. Within the same model, a second intercross alternative with individuals carrying all three QTL at the first intercross results in a 12-fold increase in the number of homozygous, animals obtained in the first intercross generation. The same ranges of decrease are observed in the number of animals to be genotyped and the number of genotypings when targeting a fixed number of homozygous animals. An option with two lines each carrying two QTL through the backcross phase and coupled with the second intercross alternative appears to be the best introgression alternative. This option requires 76 percent fewer genotypings. 68 percent fewer animals to be genotyped and costs 75 percent less than an option in which all three QTL are introgressed through a single line.

In situ hybridization was used to physically map the 5S rRNA multigene family in three selected lines of hexaploid triticale and five lines of diploid rye. Using this technique, evidence for a new locus on the 3RS arm of the three triticale lines was first obtained, as well as confirmation of the presence of 5S rRNA loci on wheat and rye chromosomes of homoeologous groups 1 and 5. The new locus on the 3RS arm was confirmed in two lines of rye, Secale cereale L., although it was not present in the other rye varieties studied. We propose that the new 5S rRNA locus be referred to as 5SDna-R3.

Annual species of the genus Medicago have attracted interest as green manure and temporary forage crops. This study was conducted to determine if randomly amplified polymorphic DNA (RAPD) markers could be used to assess the variability within and among species. Several accessions of each six species (M. scutellata Mill., M. disciformis DC., M. murex Willd., M. truncatula Gaertn., M. polymorpha L., and M. rugosa Desr.) were studied. A phylogeny reconstructed with the computer program Phylogenetic Analysis Using Parsimony-(PAUP) showed the same relationships as traditional taxonomy. Variation was present among accessions of all species. Several accessions were considerably different from others within the species (one of each M. scutellata and M. polymorpha) and four accessions of M. murex were differentiated by both morphology and RAPD banding patterns from the other accessions. These accessions may be useful to include in a core collection. Variation within accessions was present. Although the species are autogamous, the original seed collections may have been made from a number of plants in the same area. Also, some outcrossing or seed mixing may have occurred. Finally, at least 10 RAPD,primers appear to be necessary in order to develop reliable estimates of relatedness among annual Medicago accessions.

Genetic analyses were conducted on root-knot nematode populations belonging to the four major species of the genus Meloidogyne and originating from many countries throughout the world. Discrete genetic markers used in this study were random genomic DNA sequences amplified by the polymerase chain reaction (RAPD). Primers of 17-30 nucleotides with 30-55% G + C content were tested. Five of them generated a total of 74 scorable markers that provided reliable polymorphisms both between and within species. Using RAPD patterns alone or in combination, all the Meloidogyne species and populations studied could be unambiguously discriminated. Based on the presence or absence of bands, maximum-parsimony analysis of the data resulted in clustering of species and populations congruent with previous isoenzymatic and molecular data. The resulting tree confirmed the early divergence of M. hapla from the other species and also that M. arenaria is closer to M. javanica than it is to M. incognita. The boot-strap analysis significantly supported most of the specific branching observed in the topology but did not identify the three M. arenaria populations as a monophyletic group.

Twelve accessions of Triticum tauschii (Coss.) Schmal. were genetically analyzed for resistance to leaf rust (Puccinia recondita Rob. ex Desm.) and stem rust (Puccinia graminis Pers. f.sp. tritici Eriks. and E. Henn.) of common wheat (Triticum aestivum L.). Four genes conferring seedling resistance to leaf rust, one gene conferring seedling resistance to stem rust, and one gene conferring adult-plant resistance to stem rust were identified. These genes were genetically distinct from genes previously transferred to common wheat from T. tauschii and conferred resistance to a broad spectrum of pathogen races. Two of the four seedling leaf rust resistance genes were not expressed in synthetic hexaploids, produced by combining tetraploid wheat with the resistant T. tauschii accessions, probably owing to the action of one or more intergenomic suppressor loci on the A or B genome. The other two seedling leaf rust resistance genes were expressed at the hexaploid level as effectively as in the source diploids. One gene was mapped to the short arm of chromosome 2D more than 50 cM from the centromere and the other was mapped to chromosome 5D. Suppression of seedling resistance to leaf rust in synthetic hexaploids derived from three accessions of T. tauschii allowed the detection of three different genes conferring adult-plant resistance to a broad spectrum of leaf rust races. The gene for seedling resistance to stem rust was mapped to chromosome 1D. The degree of expression of this gene at the hexaploid level was dependent on the genetic background in which it occurred and on environmental conditions. The expression of the adult-plant gene for resistance to stem rust was slightly diminished in hexaploids. The production of synthetic hexaploids was determined to be the most efficient and flexible method for transferring genes from T. tauschii to T. aestivum. but crossing success was determined by the genotypes of both parents.