Seeds from four populations of E. obliqua were assayed for their allozyme genotype at three loci (alcohol dehydrogenase, malate dehydrogenase and acid phosphatase) as members of open-pollinated arrays to obtain quantitative estimates of three mating system parameters. These were (i) the pro- portion of seed derived from self-pollination as distinct from the proportion randomly outcrossed, (ii) the allele frequency in the pollen, and (iii) the within-population heterogeneity for the frequency of detectable outcrosses. The rate of selfing varied between loci and populations, but overall suggested that up to 24% of viable seed may derive from self-fertilization. This level of partial self-fertilization, together with local variation in the mating system, yielded an observed average inbreeding coefficient (Wright's fixation index) of 0.123 for these loci. In addition, the populations showed substantial differences in gene frequency at each locus. The statistical techniques appropriate for the analysis of open-pollinated progeny arrays are given in an appendix.
Pinusradiata is restricted to three mainland coastal populations in California and two island populations off Baja California, Mexico. In this study each population was divided into two geographic stands based on natural disjunctions within populations. In addition to the division mentioned above, each mainland population was also divided into a number of ecological stands based on ecological and environmental criteria. Genetic variation was measured by analysing 31 allozyme loci electrophoretically using germinated seed from 272 families across all stands and populations. Moderate levels of allozyme variation were found as shown by population averages for mean number of alleles per locus (1.79), percent polymorphic loci (46.4%, 0.99 criterion), and expected heterozygosity (0.098). In fact, the overall genetic diversity in P. radiata (HT = 0.117) is low compared with that of other conifers. In comparison with populations, the levels of allozyme variation in both ecological and geographic stands were slightly lower (means across ecological stands: A = 1.56, P = 39.3%, and He = 0.095). Of the total genetic diversity in P. radiata, 16.2% could be apportioned between populations, a high proportion for a conifer. In contrast, only 2.0 and 1.3% of the genetic diversity on average within mainland populations was between ecological and geographic stands, respectively. These results indicate a low level of genetic differentiation within populations, at least based on the ecological or geographic criteria used in this study. The implications and usefulness of these findings for the development of insitu conservation strategies are discussed.
The susceptibility of Pinusmuricata D. Don to needle blight caused by Dothistromaseptospora (Dorog.) Morelet var. septospora was investigated in three provenance tests and a progeny test in New South Wales, Australia, and compared with that in Pinusradiata D. Don, the major commercially planted species. Provenances of P. muricata from Humboldt, Mendocino, and Sonoma counties in northern California were moderately susceptible for the first 3 or 4 years but then developed a high degree of field resistance. There was a general trend to increasing susceptibility in provenances progressively southwards along the California coast, with one notable exception, Santa Rosa Island provenance, which appeared to be resistant. All provenances from Monterey southwards, with that one exception, were at least as susceptible as P. radiata. The Mendocino County provenance of P. muricata is suggested as an alternative to P. radiata for planting on sites where there is a high risk of severe needle blight, as it possesses a combination of high disease resistance, rapid growth rate, and desirable wood properties. A 6-year-old progeny test of trees of Sonoma County provenance yielded a heritability estimate of 0.29 for percentage of needles infected by Dothistroma needle blight, which is very similar to estimates for the same trait in P. radiata. This indicates that although this population is already substantially less susceptible than the most resistant provenance of P. radiata, there is still a high degree of heritable variation and resistance could be improved even further by within-provenance selection.
No abstract
••'«>) -''Uf{Received ^ JulyThe growth and survival of Eucalyptus obliqua seedlings from twenty-two provenances throughout the range of the species in south-eastern Australia were studied in three field trials in Tasmania and Victoria. Early results indicated significant variation among provenances for several growth parameters and for survival. Ranking for height was consistent on the two low-altitude planting sites and similar to that in previously reported glasshouse studies. Within provenances there were also significant differences hetween families for growth and survival. These results suggest that genetic improvement of the species is possihle, not only hy selection of the most suitable provenances for particular sites, hut also hy the selection of superior individual trees within a provenance.
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