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Characterization of amylose-free and high-amylose starch mutations in cassava : [Voir chapître Speaker presentation Wednesday S6-4]

Sanchez T., Ceballos H., Dufour D., Denyer K., Fregene M., Pérez J.C., Morante N., Rosero A.. 2008. In : Cassava : Meeting the challenges of the new millennium. Proceedings of the first scientific meeting of the global cassava partnership. Saint Louis : DDPSC, 1 p.. Cassava Meeting the Challenges of the New Millenium. 1, 2008-07-21/2008-07-25, Ghent (Belgique).

Two important starch mutations have been recently identified in cassava. The first one is an amylose-free spontaneous mutation identified in a self-pollinated progeny. SDS-PAGE demonstrated the absence of GBSS enzyme in the starch from this genotype. A single base deletion in Exon 6, leading to a frame shift that truncates GBSS protein, has been identified. This amylose-free (or waxy) cassava starch showed higher values for peak viscosity, gel breakdown and setback when analyzed in the rapid visco-analyzer. Solubility is considerably reduced, while the swelling index and volume fraction of the dispersed phase were higher. Development of a commercial waxy-starch cassava variety has begun. The second mutation was identified in the M2 generation of a mutagenized population irradiated with gamma rays. Starch granule morphology is very distinctive. Granules are smaller (average size 5.8 um) compared with wild type cassava starch (average around 15.0 um), their surface is rough and their shape is irregular. Amylose content was significantly higher (ranging from 28 to 36%) than in typical cassava starch (the average from starch samples of more than 4,000 different genotypes was 20.7%). The small-granule starch mutant produced gels showing no viscosity (5% suspensions) with low clarity. Suspension at higher starch concentrations (8-10%) resulted in very low viscosity. Preliminary results suggest that the mutation may be due to a lesion in a gene encoding one of the isoforms of isoamylase (probably isa1 or isa2). Crosses among these two mutations are underway in search of a third starch phenotype.

Mots-clés : manihot esculenta; manioc; pérou

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