Studies In Genetic Resources Of Pinus Caribaea Morelet Var. Caribaea Barr. And Golf.

Pinus caribaea is the fastest growing tropical pine that is widely planted as an exotic species in the tropics worldwide. Pinus caribaea was introduced to China in the 1960s. In the 1990s,The Chinese Academy of Forestry was provided with seeds of 16 provenances and 220 open-pollinated families which represent the whole natural range of P.caribaea var. caribaea, and the seeds was used to restablished 2 breeding seedling seed orchards (BSSO) or provenance/progeny trials in Dasha and Shishan Guangdong Province in 1995 and 1999 respectively.SSR(Simple Sequence Repeat) markers were used to study genetic diversity, population structure and breeding system of the species using capillary electrophoresis with fluorescence detection. Quantitative analysis of morphological traits was also conducted for one of the two provenance/progeny trials to estimate genetic parameters at different leveles of provenance, family and individual for growth and wood property traits. A conservation and breeding strategy were proposed based on the genetic information and performances of P. caribaea var. caribaea in China. The purpose of this study was to obtain basic information on genetic background, growth performance and wood properties of P. caribaea var. caribaea and to provide theoretical basis for genetic resources conservation and breeding strategy of the species.SSR variation was studied in three natural populations, one island population, one managed as seed stand population and exotic populations of P. caribaea var. caribaea respectively from China and Brizil. Results showed that the exotic population in Dasha was similar to the natural populations in genetic diversity, genetic differences, genetic relationship and population differentiation. It is suggested that the multiple population breeding system may be a good conservence strategy of P. caribaea var. caribaea. The genetic differences of the island population was the largest, however, the genetic distance between the island population and other populations was large. It may be the results of the influence by its geographical position and logging. A low level of the inter-population genetic differentiation of 7 populations (Fst=0.0847) and a higher estimate of gene flow(Hm=2.7014), indicated that the total variation was mainly due to genetic variation within the populations and the inter-populations of P. caribaea var. caribaea was not significant genetic drift.Mating systems in natural, management and seed orchard populations of P.caribaea var. caribaea were analysed using SSR markers. The small differences between singleocus and multilocus estimates suggest that the inbreeding detected within the variety was caused by true selfing rather than consanguineous mating. The multilocus estimate of outcrossing rates were smaller than 1.0 beside the island population. The level of selfing ranged from 11 % in the managed as seed stands population to 23 % in the seed orchard. The (minimum variance) singlelocus inbreeding coefficient of maternal parents of 5 populations was no significantly different from zero. Therefore, P. caribaea var. caribaea was a highly outcrossing spcies. The expected fixation index(Fe) at inbreeding equilibrium of the seed orchard population is greater than others, suggested that the seed orchard populations suffered inbreeding depression.Quantitative analysis of growth traits and wood traits were conducted for a field trial of P. caribaea var. caribaea located in Shishan. Significant genetic variation was found in height, diameter and stem form among provenances and families within provenance, with the Malas Aguas and Brazil provenances superior than others. Growth performance was significantly correlated with latitudes and longitudes of provenance origins. The DBH and height of provenance heritabilities were much higher than family and individual heritabilities. Results suggest that provenance selection would be the most appropriate first step for the genetic improvement of the species and substantial genetic gain could be achieved by family selection within provenance.Significant genetic variation was found in wood density, tracheid properties, chemical composition of wood among provenances, with the El Buren and Cajalbana provenances superior than others. Length and width of tracheids increased with ages, but wall thickness of tracheid had not changed much. Wood density of wood was positively correlated with length and width tracheids, but was negatively correlated with growth traits, Provenance heritabilities for some wood traits were not always higher than individual heritabilities. As a result, a breeding strategy of multiple population breeding system (MPBS) featuring simple and cheap breeding methods for the first generation and intensive breeding for advanced generations is proposed. For an exotic species, it is important to maintain a wide gentic base for breeding. The good method to establish gene archives along with the field trials using the same material to ensure all genetic diversity are captured in the gene archive.In recent years, hybrid pine (Pinus caribaea×Pinus elliottii) was very popular in Guangdong and Guangxi, however, the investment in research and development of Pinus caribaea was not sufficient, resulting in very limited production of high quality hybrid seeds n China. In many areas of southern China, the F2 hybrid seeds imported from Queensland of Australia were used. In order to get rid of long-term dependence on imported seed and to meet the domestic market demands for hybrid pine, Pinus caribaea needs to have a well developed long-term breeding strategy and a mass production program of the hybrid pine as soon as possible.