| The average global grain yield per unit area of the major staple crops, wheat, rice and maize, more than dubled in the past fifty years and this trend continues. Increased yields have been achieved by increased or extended photosynthesis per unit land area and increased partitioning of crop bimass to the harvested product. Since values of leaf area index are generally high enough at present, and the upper limit for harvest index is being approached in most bred crops, it is appropriate to further increase yield and to focus on ways of improving crop photosynthetic efficiency and increasing assimilate production genetically. Plant heterosis has been widely used in agricultural production, but the views in the genetic mechanisms of heterosis were inconsistant. The genes controlling quantitative trails were analyzed systematically in the classic quantitative genetics, but it is difficult for this method to identify single gene with mini effect and to define its precise location on the chromosome. As the molecular markers developing and studing on QTLs in recent years, these provide a new method to detect the genetic basis of plant heterosis and quantitative trait loci. The marker-based genetic analysis of heterosis and quantitative traits were studied in F2.3 generation between Lemont and Gang 46. Lemont is the female parent with high photosynthetic rate originated from United States of America, Gang 46 is the maintainer line of indica rice of chinese origin. The 160 F23 lines were replicated twice in the field following a randomized complete block design. Fourteen traits including chlorophyll content, net photosynthetic rate of single leaf, etc. were measured in Chengdu in 1999. The molecular map were constructed by using RFLP and SSR markers. The main results are as follows. 1. Among the 173 co-dominant markers anchored, the frequencies of allelic genotypes for lemont, Gang 46 and heterozygote were 22.9%~ 25.7%~ 51.3%, respectively Chisquare test indicated that distorted segregation of 36 markers was found by significant diviation from the expected Mendelian segregation ratio (1:2:1) at P 5% level. These loci distributed on 10 91 chromosomes, especially on Chromosome 3, 4, 6, 7 and 11. 27 out of 36 ditorted seqregation loci were for Gang 46, and others for Lemont. 2. A molecular map was constructed for the rice genome comprised of 180 markers (176 RFLPs and 4 SSRs) covering 12 chromosomes. The map contains 1758.7 cM with an average interval size of 7.77 eM, which well integrated the markers from the other maps. 3. A total of 36 QTLs for fourteen traits were identified by interval mapping. The number of QTLs for each trait is quite different. Senven QTLs with highest number for chlorophyll a content were identified, and only one QTL both for net photosynthetic rate and leaf area was detected espectively. Single QTL explained 6.4%-25.0% of the genotypic variation. All coincided with QTLs for each trait account for 7.1%-43.9% of the phenotypic variation. 4. For the most traits, both positive and negative additive effects were dispersed in both parents?genome. For the same trait, the parent with the lower value of the phenotype contains positive effect QTL, one with the high. value of the phenotype including negative effect QTL. About 44.4% of all QTLs had allelic effects opposite to those predicted by the parental phenotypes. 5. The digenic interactions were detected in the entire genome. All...
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