Mutation breeding for in planta modification of amylose starch in cassava (Manihot esculenta, Crantz)
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Cassava provides more dietary energy per unit area than any staple crop but native cassava starch has limited food and industrial applications. Different transgenic biotechnology approaches and ex situ physical and chemical starch modifications have been used to obtain desirable traits suitable for various food applications. But consumers are skeptical about the safety of the genetically modified foods and chemical residues. To meet the demand, gamma irradiation (this is energetic electromagnetic wave) which does not leave any residue, was used as a tool to induce in planta variation in amylose production. The four highest amylose producing plants N441P54 (32.7%), N223P12 (31.1%), N373P2 (27.2%), N329P11 (26.8%) and four lowest amylose producing plants N96P16 (14.0%), N353P6 (13.9%), N166P2 (13.2%), N476 P22 (11.7%) observed in the M1V2 generation were found to be significantly different from any one of the four controls HO008 (19.7%), HO001 (22.0%), UCC090 (22.6 %) and UCC026 (20.9%). Mutation is uncontrollable and could also lead to unexpected useful mutants. From this study four unexpected putative free-sugar mutants were identified, which could be used for bioethanol and glucose syrups production; two exceptional deep fissured and flaky mutants for the food industry; seven mutants with transition from A- to C-types of X-ray diffraction patterns with very high levels of crystallinity indexes suitable for replacing acid modified starches in pressing tablets in the pharmaceutical industries were discovered. Based on DSC classification, three gelatinization categories were observed. These were plants without gelatinization transition, plants with gelatinization transition and plants with merged gelatinization and melting transitions, occurring within gelatinization zone during calorimetric scanning from 25 – 110°C. The first and third categories included most of the putative mutants described in the research chapters and they were suitable for shortening the starch processing time required in most commercial starch applications in industry.