Phenotypic And Genetic Diversity Studies On Selected Rice (Oryza Sativa L.) Genotypes Based On Amylose Content And Gelatinization Temperature

ABSTRACT

Rice cooking and eating qualities are mostly determined by the grain’s starch content which is composed of amylose and amylopectin. Amylose content is regarded as the most important indicator in classifying rice varieties in terms of starch content. Waxy gene located on chromosome 6 codes for Granule Bound Starch Synthase (GBBS) enzyme which is involved in biocatalysis of amylose synthesis in rice endosperm. In addition, amylopectin content influences gelatinization temperature in rice. Alk gene located on chromosome 6 codes for soluble Starch Synthase II (SSII) enzyme involved biocatalysis of amylopectin. Accurate evaluation of these two traits is difficult and has hindered development of better varieties with good eating and cooking qualities by rice breeders both in Kenya and Tanzania. The aim of the study was to carry out phenotypic characterization and genetic diversity studies on selected rice (Oryza sativa L.) genotypes from Kenya and Tanzania based on amylose content and gelatinization temperature using microsatellite markers. Measurement of 7 grain and kernel traits were determined among 13 rice genotypes studied. Genetic diversity based on amylose content and gelatinization temperature was studied using 8 microsatellite (SSR) markers tightly linked to major QTLs controlling these two traits. Furthermore, presence or absence of waxy and alk genes was determined using markers tightly linked to these two genes. Minitab 15.0 and Power marker version 3.25 softwares were used to analyze the data. A dendrogram was constructed from data set of mean values of grain and kernel traits and showed two super clusters; I and II. The number of alleles per locus ranged from 2 to 4 with an average of 2.75 alleles across 8 loci. The polymorphic information content (PIC) values ranged from 0.2920 (RM 202) to 0.6841 (RM 141) in all 8 loci with an average of 0.4697. Pair-wise genetic dissimilarity coefficients ranged from 0.9003 to 0.2201 with an average of 0.5627. Maximum genetic similarity was observed between R 2793 and BS 17, Supa and IR 64, R 2793 and ITA 310, Saro 5 and ITA 310, Saro 5 and R 2794. Minimum similarity of was observed between Wahiwahi and BW 196, IR 64 and BW 196. The dendogram based on cluster analysis by microsatellite polymorphism grouped 13 rice genotypes into 2 groups effectively differentiating Kenyan and Tanzanian rice genotypes based on amylose content and gelatinization temperature. The waxy gene was amplified in 5 rice genotypes while alk gene was amplified in all the rice genotypes studied. The results obtained suggested that grain and kernel traits measurements and use of SSR markers tightly linked to genes or Quantitative Trait Loci (QTLs) controlling these two traits could effectively be utilized for diversity analysis among diverse rice genotypes.