Molecular Linkage Map Construction And Preliminary QTL Analysis Of Hevea Brasilienses

Natural rubber plays an important role in national economy and security since its specific characteristics, although the industry is strictly confined by the ecological conditions in China. The demand of natural rubber is increasing rapidly along with Chinese economic development. The recent self-support is declined to 1/3 from 1/2 in 1990s.New planting material innovation becomes a formidable work since rubber tree improving requires a long evaluation period, relatively poor in genetic fundamental studies, as well as the narrow genetic bases.Rubber tree breeding and selection is a procedure of create new seedling populations and evaluate superior individuals. In order to shorten breeding cycle and improve selection efficiency, a variety of yield prediction methods are invented, such as young tree test tapping, puncture test, morphological prediction, leaf vein latex test, petiole latex test, and so on. However, these phenotypic tests may be greatly affected by environmental factors. Studies on genes or DNA segments related to rubber tree growth, yield and latex physiological characters could be informative.An AFLP linkage map is constructed using an artificial cross between two commercial Hevea brasiliensis clones, GT1 and IAN873. The F1 population is composed of 195 seedlings. 174 DNA samples were extracted. 13 EcoRI and MseI primers were selected. AFLP electrophoresis was conducted by ABI PRISM377 DNA Sequencer. There are 487 loci accord with Medal segregation among 675 poly-morphological loci. The map is consist of 261 markers and can be divided to 18 linkage groups. Group 1 is the longest with a distance of 125.64cM, contains 43 markers. Group 16 is the shortest with a distance of 47.55cM, contains 7 markers. Group 9 and 11 contain the least makers, both contain 5 markers. The total distance of the map is 1455.57cM. The average interval is 5.58cM.The seedling trial was established in Yunnan Institute of Tropical Crops in 1999. The range of girths (100cm above ground) of the population was from 26.50 to 36.00 cm; the variation is 0.209 in 2006. The ranges of average yield of first 3 tapping (A3) and next five tapping (A5) were 0.97 to 2.28 g/t/t and 1.43 to 3.45g/t/t; the variations were 0.588 and 0.589 in 2003. The trees were tapped in 2006 again, the range of B3 and B5 were 1.55 to 4.85g/t/t and 3.12 to 7.80g/t/t, and the variations were 0.684 and 0.564 respectively. The dry rubber contents of latex (DCR %) were ranged from 30.53% to 38.32%, the variation was 0.159. The contents of sucrose (Sue) were ranged from 10.48 to 19.88mM, the variation was 0.427. The contents of inorganic phosphorus in latex (Pi) were ranged from 17.73 to 25.53mM. the variation was 0.298.Thiol contents in latex (R-SH) were ranged from 0.26 to 0.46mM, the variation was 0.432. The trait segregations were normally distributed which indicated the physiological parameters could be analyzed by QTL scanning.Composite interval mapping method was employed in this study. There were 13 putative QTL were related to tree girth. Three of them showed positive additive effect while 10 showed negative additive effect. Phenotypic variation explained (PVE) by the putative QTL varied from 10.90% to 20.74%. Only two QTL were related to DCR%. Both showed positive additive effect, and PVE were 5.39. There were 10 QTL related to Sucrose content. 6 of them showed positive additive effect while 4 loci showed negative effect. PVE varied from 19.67% to 31.00%. There were 10 QTL related to R-SH content in latex. 4 of them were showed positive while 6 showed negative additive effect. The PVE ranged from 28.41 % to 34.25%.There were 13 QTL detected related to A3. 4 of them showed positive additive effect while 9 showed negative. The PVE ranged from 13.48% to 21.25%. There were 14 QTL related to A5, 8 of them showed positive while 6 loci showed negative additive effect. The PVE ranged from 10.08% to 22.86%. There were 9 loci showed the same position and additive effect in A3 and A5. The PVE varied from 10.08% to 22.50%.There were 16 QTL related to B3. 6 of them showed positive additive effect while 10 showed negative. The PVE ranged from 12.28% to 29.66%. There were 9 QTL related to B5, 5 of them showed positive while 4 loci showed negative additive effect. The PVE varied from 17.11% to 35.37%. There were 6 loci showed the same position and additive effect in B3 and B5. The PVE varied from 21.44% to 35.37%.No common QTL was detected among the 4 yield trait test, i e A3, A5, B3 and B5. However, 4 loci were common in 3 test tapping. Two loci showed positive and the other two showed negative additive effect. The PVE ranged from 17.83% to 24.42%.A quantitative model is lacked for evaluation yield and growth potential of the rubber tree according to latex physiological parameters. The yield and growth of the individuals could not be adjusted by the physiological parameters in this study.It is very hard to establish multi-backcross inbred lines or near-isogenic lines for rubber tree like annual crops. Nevertheless, the mapping population of rubber tree can be conserved easily. Once the map is well constructed, the agronomic traits can be evaluated by many ways. So the strategy will be useful for improving yield, growth, disease or cold resistance of the tree.