Genetic And Heterosis Analysis Of Grain Appearance Quality In Rice

environmentally sensitive.Another important finding of this study was that genetic by environment interactions(GEIs) were trait and gene(QTL) specific.The four traits differed considerably with respect to the effects of QEs.QE had larger effect on CD and LWR,accounting for 14.07%and 17.78%of the phenotypic variation,respectively.Very little of the phenotypic variation observed for GL and GW was due to QE only accounting for 2.77%and 2.15%of the variation,respectively.Some QTLs(e.g.ck4b, gl7a,gw5 and lw3b) had only additive main effects,while others(e.g.ck3,gl3 and lw9) also had an additive×environment interaction effects.The information obtained in this study should be very useful for manipulating the QTLs for these traits by molecular MAS.(2) A total of 217 Near-Isogenic Introgression Lines(ILs) in the Teqing background with introgressed Lemont segments were analyzed using 160 rice microsatellite markers. The donor segments from different chromosomes and chromosomal locations were introgressed into the recipient genome in different frequencies,suggesting that some known internal mechanisms could affect the transmission of genomic segments.The total introgressed segments were highest in chromosome 4 and lowest in chromosome 7.The average donor genomic portion in the ILs was 10.30%,ranging from 0 to 35%.The mean number of donor segments in a IL was 8.7 with 17.8 cM average length of introgressed segments.A set of 56 lines was selected to build ILs in Teqing background with approximately 3 to 7 lines for each chromosome.There are a few introgressive segments on none target regions requiring further elimination by marker-aided backcrossing.(3) The ILs with Teqing genetic background were used to dissect the genetic basis of CD,GL,GW and LWR by using QTL Network 2.0.Some of the main QTLs which were detected in the RILs,such as qCD-7,qGL-7 and qGW-7,were also identified in the ILs. But there are still some differences about the two populations.A major QTL(qGW-2) was detected for GW contributing 28.05%of the phenotypic variance.Surprisingly,the major QTL was not identified in the RILs.This may be due to the different genetic background.Among these QTLs,one common QTL for CD,GL and GW in interval OSR4-RM505 on chromosome7 was identified.This QTL also was identified in the RILs. A common QTL for CD,GW and LWR in interval RM439-RM340 on chromosome 6 was also identified.These results suggested that there were some differences in QTLs between the RILs and ILs.Moreover,there were some common QTLs for the closely relative traits at the same or near chromosome regions.(4) Ninety-three parents including IR75589-31S,IR60,IR70 and ninety recombinant inbred lines or advanced backcrossing introgression lines with different indica-japonica degrees were chosen to compare four characters of grain quality between F₁ hybrids and their parents.Based on the relative heterosis for all characters in all hybrids,the frequency of positive mid-parent heterosis was higher than that of negative mid-parent heterosis except for LWR.Grain appearance quality among F₁ hybrids varied significantly with greatest variation on CD.The performance of most F₁ hybrids for all the four characters was between the low-value parent and high-value parent.F₁s were found to be highly correlated with the male parent,female parent and average of the parents for all the four characters.Correlation analyses also revealed different relationships among the four characters tested.CD was significantly negatively correlated with GL(R=-0.5628^**) and LWR(R=-0.7498^**) but positively correlated with GW(R=0.7539^**).The results of path analysis showed that magnitudes of direction from GL,GW and LWR to CD were-1.9409,2.1738 and 2.7805,respectively. Regression analysis of rice grain appearance traits resulted in linear regression equation between CD(y) and GL(x₁),GW(x₂),LWR(x₃) of y=-39.892x₁+141.389x₂+77.341x₃ -269.906.This shows that GW is the most important factor affecting rice CD.The genetic distance of the rice parents and the relativity analysis were determined using SSR markers.The genetic distance between three female and ninety male based on 161 SSR markers varied in the range from 0.2914 to 0.4205 with an average of 0.3520.The relative coefficients between SSR genetic distance and heterosis of four grain appearance traits were partial to small(CD=-0.0307,GL=-0.1358,GW=0.1147,LWR=-0.1408). The genetic distance of rice parents selected and the grain appearance heterosis was not significantly correlated.Because of this,SSR markers selected in this study couldn't predict rice appearance quality heterosis,thus,the genetic analysis based on molecular markers predicting the grain appearance quality needs further studies.(5) The genetic effect of appearance quality traits on hybrid rice were studied by using the genetic model and analysis method for quality traits.The results indicated that all appearance quality traits were mainly influenced by directive additive variance(V_A) and maternal additive variance(V_Am).GL,GW and LWR were controlled mainly by directive effects and less by maternal additive effects.CD on the other hand,was mainly controlled by direct additive and maternal additive effects.GL,GW and LWR had very high narrow sense heritability values(86.03%,89.70,and 83.78%,respectively) while CD had relatively lower narrow sense heritability(72.94%).Heritability for all the four grain appearance traits was more of direct heritability than maternal heritability.