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SVERIGES LANTBRUKSUNIVERSITET (2004)

Genetic variability and biotechnological studies for the conservation and improvement of Ensete ventricosum (Ethiopia, Agrobacterium, Leuconostoc, Torulaspora)

Birmeta, Genet

Titre  : Genetic variability and biotechnological studies for the conservation and improvement of Ensete ventricosum (Ethiopia, Agrobacterium, Leuconostoc, Torulaspora)

Auteur  : Birmeta, Genet

Université de soutenance : SVERIGES LANTBRUKSUNIVERSITET (SWEDEN)

Grade : Doctoral Thesis 2004

Résumé
Enset (Ensete ventricosum) is a drought-resistant staple food crop which is grown in the south and south-western parts of Ethiopia. Due to lack of research on enset, no benefits have yet been gained from modern biotechnological approaches. This thesis deals with studies on genetic diversity in cultivated and wild enset, development of micropropagation and transformation procedures and identification of microbes associated with enset. The genetic diversity in cultivated enset from nine enset-growing regions of Ethiopia was investigated using Random Amplified Polymorphic DNA (RAPD). All of the 111 enset clones studied showed unique band patterns. The genetic diversity observed in cultivated enset in a particular area appears to be related to the extent of enset cultivation and the culture and distribution pattern of the different ethnic groups than geographical distance. RAPD was also applied to document genetic diversity in 5 wild enset populations in Ethiopia together with some cultivated enset clones and Musa species. Both studies indicated that the genetic diversity within populations was higher than that of among populations. Our results suggest that the current cultivated clones have originated from a limited number of wild progenitors. The large gene pool observed in the species could be utilized for improvement of the crop. Two studies focused on the development of efficient micropropagation and transformation procedures for enset in order to develop optimal systems for genetic improvement of the crop. The micropropagation procedure developed enabled the production of large numbers of propagules. Wounding the meristem and modifying the nutrients in the medium was essential to enhance the efficiency of micropropagation. In the transformation experiment, expression of β-glucuronidase (gus) gene was manifested in different explants of two enset clones, using both particle bombardment and Agrobacterium. Agrobacterium was shown to infect the monocot plant resulting in higher percentage (63%) of GUS expression than bombardment (18%), when shoot tips were sonicated. The frequency of GUS expressing explants appears to vary depending on sonication treatment, tissue type, co-culture period and transformation techniques. Microbial contamination, in particular by apparently endophytic microbes that are resistant to antimicrobial agents was encountered during micropropagation work. This persistent problem prompted a microbiological study with identification of 16 bacteria, 7 yeasts and 1 unknown mycelial fungus from surface-disinfected in vitro and field-grown enset clones using 16S and 26S rDNA sequences. Some of the microbes identified could be pathogenic in field-grown enset.

Mots clés : Agrobacterium, endophytic contamination, genetic diversity, Leuconostoc, microorganisms, micropropagation, Musaceae, particle bombardment, Pseudomonas reactans, RAPD, rDNA, transformation, Torulaspora

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Page publiée le 20 septembre 2005, mise à jour le 17 juin 2017