Genetic Relationship Among Wx Gene, AC, GC And GT Of Rice And Comprehensive Evaluation Of Breeding Lines' Quality Traits

Amylose content(AC), gel consistency(GC) and gelatinization temperature(GT) are three important aspects that evaluate the cooking and eating quality of rice. It is generally considered that AC is controlled by Wx gene, located at the short arm of chromosome 6 in rice. At the same time some minor genes also influenced AC. At present time, there is some debate about genetic relationship among Wx gene, AC, GC and GT of rice. Studies on the genetic relationship among Wx gene, AC, GC and GT of rice not only make for exploring the genetic mechanism of GC and GT but also help to improve the cooking and eating quality of rice.We tested the Wx genotype by the PCR-Acc I molecular marker and investigated AC, GC and GT of our experiment material to explore the genetic relationship among Wx gene, AC, GC and GT of rice. On the other hand, we analyzed quality traits of some breeding lines comprehensively. The VCR-Acc I molecular marker and the way of genetic background's analysis were also used in the course. The result would offer reliable data for selecting breeding material finally. The major results are as follows:1. By testing Wx genotype and investigating amylose content (AC), gel consistency (GC) and gelatinization temperature (GT) of 60 indica varieties (or lines) and 57 B3F5 breeding lines of G46B/D Xiang 1B , the genetic relationship among Wx gene, AC, GC, and GT of rice was analyzed. The results showed that there were significant negative correlations between AC and GC, with -0.836 and -0.906 of correlation coefficients in the two groups material, respectively. Moreover, both of AC and GC were closely related to Wx genotypes, i.e. the materials with GG-type of Wx gene had higher AC and harder GC, however, the materials with TT-type of Wx gene had moderate AC and softer GC. Because it was true that the AC of rice grain was controlled by Wx gene. So the result indicated that GC would be controlled by Wx gene or by one locus tightly linked to this gene.2. In all 57 B3F5 lines, AC ranged from 20.4% to 27.0% with the mean value of 24.9% and GC from 25mm to 31mm with the mean value of 27mm in 26 lines with GG-type of Wx gene, however, AC ranged from 10.8% to 13.4% with the mean value of 11.8% and GCfrom 46mm to 77mm with the mean value of 57mm in 31 lines with TT-type of Wx gene. So the GG-type of lines always had high AC and hard GC, the TT-type of lines always had moderate AC and soft GC, and no recombiant lines were found. In other words high or low AC and hard or soft GC were cosegregated with Wx genotypes. These results suggested that AC was mainly controlled by Wx gene and GC was also controlled by Wx gene or by one locus tightly linked to this gene.3. GT was not significantly related to AC and Wx genotype in 60 indica varieties. For the varieties that had different AC or Wx genotypes, the range of GT was the same on the whole. For example, according to Wx genotypes, GT of 21 varieties with GG-type of Wx gene ranged form 3.3 to 7.0 with the mean value of 4.9, however, GT of 39 varieties with TT-type of Wx gene ranged from 3.0 to 7.0 with the mean value of 5.2. So it was inferred that the locus controlling GT was not Wx locus.4. The Wx genotype of 37 breeding lines was tested by PCR-Acc I molecular marker. At the same time, their quality traits were also analyzed comprehensively. Among them, we selected 14 lines that not only had homozygous Wx genotype but also excellent milling quality and appearance quality.5. 16 B3F5 lines and 5 BjFg lines were selected from the 37 breeding lines and their genetic background were analyzed by 40 polymorphic SSR primers that were selected from 324 SSR primers distributing all chromosomes of rice. The result showed that the average genetic similarity index with G46B was 90.0% in the 16 B3F5 lines, among which the highest was 98.8%, and 66.7% in the 5 BiF8 lines, among which the highest is 76.3%.6. Based on the above-mentioned results, we screened out several breeding lines i.e. the No.25, No.26, No.29 and No.30 lines that had better quality traits than G46B and higher genetic similarity index with G46B.