Genetic Characterization of Chinese fir from Six Provinces in Southern China and Construction of a Core Collection.

Large ex situ germplasm collections of plants generally contain significant diversity. A set of 700 well-conserved Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) clones from six provinces in southern China in the ex situ gene bank of Longshan State Forest, was analyzed using 21 simple sequence repeat markers, with the aim of assessing the genetic diversity of these germplasm resources. Genetic analysis revealed extensive genetic variation among the accessions, with an average of 8.31 alleles per locus and a mean Shannon index of 1.331. Excluding loci with null alleles, we obtained a low level of genetic differentiation among provinces, consistent with the interpopulation genetic variation (1%). Three clusters were identified by STRUCTURE, which did not match the individuals' geographical provenances. Ten traits related to growth and wood properties were quantified in these individuals, and there was substantial variation in all traits across individuals, these provide a potential source of variation for genetic improvement of the Chinese fir. Screening large collections for multiple-trait selective breeding programs is laborious and expensive; a core collection of 300 accessions, representative of the germplasm, was established, based on genotypic and phenotypic data. The identified small, but diverse, collections will be useful for further genome-wide association studies.

Somatic Embryogenesis of Immature Cunninghamia lanceolata (Lamb.) Hook Zygotic Embryos.

Two efficient somatic embryogenesis systems were developed in Chinese fir, the most important conifer for industrial wood production in China. Three development stages (cleavage polyembryony, dominant embryo, and precotyledon) of immature embryos derived from 25 genotypes of open-pollinated mother trees were used as initial explants. Cleavage polyembryony-stage embryos with a 12.44% induction rate was the most embryogenic response stage. The highest frequency of embryogenic callus (13.86%) induction was obtained from DCR medium supplemented with 1.5 mg L-1 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.3 mg L-1 kinetin (KN). An average of 53.33 early somatic embryos were produced from approximately 0.2 g (fresh weight) embryogenic callus after 2 weeks of incubation on medium supplemented with 50 µmol L-1 abscisic acid (ABA) and 100 g L-1 polyethylene glycol (PEG) 6000. About 53% dominant embryos have an embryogenic response after a 6-week cultivation on medium supplemented with 1.0-2.0 mg L-1 benzyladenine (BA), 0.2 mg L-1 naphthylacetic acid (NAA) or 2,4-D, and 0.004 mg L-1 thidiazuron (TDZ). After three successive transfer cultures on medium supplemented with 1.5 mg L-1 BA, 0.2 mg L-1 NAA, and 0.004 mg L-1 TDZ, 4.49-16.51% of the embryos developed into somatic embryos.