Evaluation of the effects of the waxy starch mutation and environment on yield and starch functional properties of cassava

Abstract

Cassava roots are one of the most important sources of starch on a global scale. Two aspects of cassava as a starch crop were studied in this thesis work; 1) determining if the amylose-free (waxy) mutation is coupled with a reduction in yield, and 2) the environmental impact on yield, yield components and starch functional properties of cassava. The waxy trait, resulting from a mutation in the GBSS locus, is in several other crops associated with a yield penalty. In this study, siblings from eight full-sibling families, segregating for the waxy trait, were used to determine if the waxy mutation has implications for yield, dry matter content and harvest index in cassava. The only significant effect of starch type was on the dry matter content, with the waxy clones having a 0.8% lower dry matter than their wild type siblings. The environmental effects on cassava yield and starch functional properties were examined by comparing data from two contrasting environments of Colombia; the Cauca river valley and the Caribbean coast. Significant differences were found in yield, dry matter content and harvest index between cassava clones from different environments. There were significant effects of environment on starch pasting properties, solubility and dispersed volume fraction. Starches from the higher temperature, Caribbean coast had an elevated pasting temperature (5°C higher for waxy starches and 3.6° C for wild type), whereas the peak viscosity was lower in starches from this environment (114 cP lower in waxy starch and 205 cP in wild type). The gravimetric method for determining dry matter content in cassava roots was also evaluated