Evaluation of cassava (Manihot esculenta Crantz) germplasm collections using RAPD markers

Des marqueurs RAPD sont combinés avec une analyse de calcul de distance (simple matching) afin d'évaluer les relations génétiques entre les cultivars africains de manioc. Une étude préliminaire sur 3 espèces avec 20 "primers" montre clairement que ces marqueurs peuvent être très utiles. L'ADN de 19 cultivars a été amplifié en utilisant 8 primers. Les cultivars se discriminent bien et sont distribués de manière cohérente si on compare aux résultats obtenus avec les RFLP ou isoenzymes. La diversité génétique, la caractérisation des collections et les études d'introgression sont les domaines que les RAPD peuvent contribuer à améliorer pour le manioc. (Résumé d'auteur

An assessment of genetic diversity within a collection of cassava (Manihot esculenta Crantz) germplasm using molecular markers

Des clones cDNA de Manioc (#Manihot esculenta Crantz) ont été utilisés pour détecter le polymorphisme de longueur des fragments de resriction (RFLP) dans une collection de germplasm de manioc conservée en culture #in vitro au centre ORSTOM de Montpellier. La collection se compose principalement de cultivars africains de #M. esculenta, ainsi que de quelques #M.glaziovii Mueller Von Argau and #M. caerulescens Pohl, et de quelques hybrides interspécifiques de #M. esculenta x #M. glaziovii$. Les sondes cDNA mettent à jour des niveaux de polymorphisme significatifs à la fois à l'intérieur et entre les espèces ; ce qui est suffisant pour créer des dendogrammes indiquant la diversité génétique à l'intérieur de la collection. (Résumé d'auteur

Analysis of heterogeneity of Copia-like retrotransposons in the genome of Cassava ( Manihot esculenta Crantz)

Retrotransposons are ubiquitous in eukaryotic genomes and now proving to be useful genetic tools for genetic diversity and phylogenetic analyses, especially in plants. In order to assess the diversity of Ty1/Copia-like retrotransposons of cassava, we used PCR primers anchored on the conserved domains of reverse transcriptases (RTs) to amplify cassava Ty1/Copia-like RT. The PCR product was cloned and sequenced. Sequences analysis of the clones revealed the presence of 69 families of Ty1/Copia-like retrotransposon in the genome of cassava. Comparative analyses of the predicted amino acid sequences of these clones with those of other plants showed that retroelements of this class are very heterogeneous in cassava. Cassava is widely grown for its edible roots in the tropical and subtropical regions of the world. Cassava roots, though poor in protein, are rich in starch (makes up about 80% of the dry matter), vitamin C, carotenes, calcium and potassium. It has a great commercial importance as a source of starch and starch based products. Realizing the importance of cassava, it stands out as a crop to benefit from biotechnology development. Heterogeneity of Mecops (Manihot esculenta copia-like Retrotransposons) showed that they may be useful for genetic diversity and phylogenetic analyses of cassava germplasm

Oxidative stress responses during cassava post-harvest physiological deterioration

A major constraint to the development of cassava (Manihot esculenta Crantz) as a crop to both farmers and processors is its starchy storage roots' rapid post-harvest deterioration, which can render it unpalatable and unmarketable within 24 72 h. An oxidative burst occurs within 15 min of the root being injured, that is followed by the altered regulation of genes, notably for catalase and peroxidase, related to the modulation of reactive oxygen species, and the accumulation of secondary metabolites, some of which show antioxidant properties. The interactions between these enzymes and compounds, in particular peroxidase and the coumarin, scopoletin, are largely confined to the vascular tissues where the visible symptoms of deterioration are observed. These, together with other data, are used to develop a tentative model of some of the principal events involved in the deterioration process. Abbreviations: ACMV, African cassava mosaic virus; AFLP, amplified fragment length polymorphism; CAT, catalase; cDNA, complementary deoxyribonucleic acid; CIAT, International Centre for Tropical Agriculture; Cu/ZnSOD, copper/zinc superoxide dismutase; DAB, 3,3-diaminobenzidine tetrahydrochloride; DPPH, 1,1-diphenyl-2-picrylhydrazyl; FeSOD, iron superoxide dismutase; FW, fresh weight; GUS, ?-glucuronidase; HPTLC, high-performance thin-layer chromatography; HR, hypersensitive response; IEF-PAGE, isoelectric focusing polyacrylamide gel electrophoresis; MAS, marker-assisted selection; MeJa, methyl jasmonate; MnSOD, manganese superoxide dismutase; NADPH, nicotinamide adenine dinucleotide phosphate (reduced form); NBT, nitroblue tetrazolium; PAL, phenylalanine ammonia-lyase; PCD, programmed cell death; PCR, polymerase chain reaction; POX, peroxidase; PPD, post-harvest physiological deterioration; QTL, quantitative trait loci; ROS, reactive oxygen species; RT, room temperature; SAR, systemic acquired resistance; SDS, sodium dodecyl sulfate; SOD, superoxide dismutas

Mapping wound-response genes involved in post-harvest physiological deterioration (PPD) of cassava (Manihot esculenta Crantz)

The genome locations of the wound-response genes that were expressedduring the post-harvest physiological deterioration (PPD) of cassava, suchas phenylalanine ammonia lyase, ?-1.3 glucanase, hydroxyprolinerich glycoprotein, catalase, 1-aminocyclopropane 1-carboxylate, cysteineprotease inhibitor, aspartic protease, a partial cDNA for serine/threonineprotein kinase and peroxidase, have been identified on the frameworkmolecular genetic map of cassava. Also, molecular markers linked toputative quantitative trait loci (QTLs) influencing PPD of cassava weremapped using an F1mapping population derived from elite parentallines (TMS 30572 × cm 2177-2). A molecular linkage map previouslyconstructed based on the segregation of 240 RFLP, 100 RAPD, 85microsatellite and five isoenzyme markers on 144 F1 individuals wasused for the QTL mapping.A set of 10 molecular markers with a significant association with putativeQTLs for PPD were identified based on probability values < 0.005in order to minimize the detection of false positives. Based on single-markerregression, eight putative QTLs located on the linkage groups G, P, L, U,and X of the female-derived framework map were found to explain between 5 12% of the phenotypic variance of the PPD. In the male-derived frameworkmap, two putative QTLs on linkage groups C and L explained 13% and11% of this variance, respectively. This study thus identified the majorgenome regions of cassava related to physiological post-harvestdeterioration, thereby providing tools for the identification of gene(s)controlling this trait

Hydroxyproline-rich glycoproteins expressed during stress response in cassava

The storage roots of cassava (Manihot esculenta Crantz) suffer from a rapid post-harvest deterioration that is a major constraint to their increased exploitation. In many ways this deterioration resembles wound responses in other better studied plant systems, though it appears to lack an adequate wound repair response. A cDNA clone (cMeHRGP1) for a hydroxyproline-rich glycoprotein expressed during the deterioration response was isolated and characterised. This clone proved to be an antisense pairing, coding for part of phosphoserine aminotransferase on its complementary strand. Messenger RNA corresponding to cMeHRGP1 accumulated in deteriorating cassava roots from day three after harvest, by which time the deterioration response was well advanced. There by confirming that aspects of the wound repair response were inadequate in harvested cassava roots