Prediction of high and intermediate amylose groups based on the starch physicochemical properties in rice (Oryza sativa L.) genotypes

In order to investigate the relationship among amylose content, gelatinization temperature and paste viscosity properties and identifying the discriminator parameters of intermediate and high amylose groups in rice genotypes, 40 pure lines and cultivars from two groups of high and medium amylose content were evaluated in a randomized complete block design with three replications at Rice Research Institute of Iran during 2015 and 2016. Physicochemical characteristics of grain (amylose content, gelatinization temperature) and paste viscosity properties including peak viscosity, trough viscosity, breakdown viscosity, final viscosity, setback viscosity and consistency viscosity were measured by Rapid Visco Analyser in RVU unit. Results of cluster analysis with WARD method showed that all selected rice genotypes from high and intermediate amylose groups were classified into two groups based on paste viscosity characteristics and gelatinization temperature. The first group consisted of 19 genotypes with high amylose content and the second group included 21 genotypes with intermediate amylose content. In fact, the classification of the genotypes based on the viscosity parameters and gelatinization temperature was similar to the classification of the cultivars based on the amylose content of grain. Discriminant function analysis showed that only the final viscosity and gelatinization temperature completely (100%) separate the high and intermediate amylose groups and identified as the best and most effective discriminators (with an eigenvalue of 56.35) that are easier, less cost and time consuming, compared to direct measurement of amylose content of grain. Evaluation of starch viscosity characteristics and gelatinization temperature of rice grain in combination with multivariate statistical methods may be considered as an easier and less costly method suitable for the classification of rice genotypes and may be used in breeding programs to identify good grain quality rice cultivars. According to the fitted regression model, it is possible to predict the intermediate to high amylose groups of rice genotypes in regard to final viscosity value between 290.50 and 493.25 RVU with an adjusted R square of 97%.