69 several cases, for example A. auriculiformis in Thailand (LUANGVIRIYASAENG and PINYOPUSARERK, 1998). Build-up of inbreeding through self-fertilization occurring in isolated trees or poorly-flowering stands used for seed collection over successive generations, and the associated depression of vigour that we have demonstrated in this study, could explain this phenomenon. 185-195 (1996) Acknowledgments AbstractThis screening study analyzed ploidy levels by counting the chromosome number of 61 Aigeiros cultivars grown in China. Triploid Aigeiros has been found in four of these cultivars: Populus x euramericana (Dode) Guiner cv. Wuhei-1, P. x Liaohenica, P. Langfangensis-3 Wang (P. deltodide Barry cv. "Shanhaiguan" x P. simonii x P. pyramidalis-12 + Ulmus pumila Linn.), and P. x euramericana (Dode) Guinier. cv. "Zhonglin-46". The karyotype analysis indicates that triploid Aigeiros might be derived from original allotriploid. Because growth of the triploid trees was faster than their respective diploid hybrids or clones in the plantations where we collected the materials, we expect that they will play a significant role in breeding, reforestation and fiber production in China.

Six simple sequence repeats (SSR) markers were developed from expressed sequence tags (ESTs) in the genus Larix. Based on evaluation with 49 L. kaempferi genotypes, the number of alleles per locus ranged from two to four, and the expected (He) and observed (Ho) heterozygosity values were 0.225−0.694 and 0.201−0.656, respectively. The inbreeding coffcient (F IS ) for all loci were less than zero except that LAReSSR85 was 0.4383. All the six EST-SSR markers were transferable to L. gmelini, L. olgensis var Koreana, L. principisrupprechtii and L. olgensis. BlastX analysis showed that five of the EST-SSRs were homologous to known genes. The six EST-SSR markers developed here can be valuable for biological applications in Larix.

The Inter-Simple Sequence Repeat (ISSR) was used in this study for genetic fingerprinting and identification of 28 important Populus L. (poplar) cultivars (varieties/ clones), and determination of the genetic relationships among these cultivars. These 28 cultivars belonged to sections Aigeiros, Tacahamaca, Leuce, Turanga, and hybrids between sections Aigeiros and Tacahamaca. Out of 27 ISSR primers tested, eight primers generated clear multiplex profiles. The best three primers produced 154 easily detectable fragments, 129 (84%) of which were polymorphic among the cultivars. Each of these 3 primers produced fingerprint profiles unique to each of the accessions studied, and thus could be solely used for their identification. Twenty-five markers, unique to 10 of the cultivars studied, were detected. These markers may be converted into cultivar-specific probes for identification purposes. Genetic relationships among the cultivars were evaluated by generating a similarity matrix based on the simple matching coefficient and the unweighted pair group method with arithmetic average (UPGMA) dendrogram. The results showed a clear-cut separation of cultivars among different sections of poplar, and were in agreement with the genealogy of the sampled cultivars. The present study shows that ISSR markers could generate abundant polymorphism, are reproducible, and are quick for characterization of poplar cultivars. In the future, the markers used in this study, in combination with other molecular techniques, could provide a useful panel of ISSR markers for largescale DNA fingerprinting of poplar cultivars and determination of the genetic relationships among these cultivars.