Proceedings of the 27th Southern Forest Tree Improvement Conference
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Item Loblolly Pine Karyotype Using FISH and DAPI Positive Banding(2003) Islam-Faridi, M. N.; Nelson, C. D.; Kubisiak, T. L.; Gullirmo, M. V.; McNamara, V. H.; Price, H. J.; Stelly, D. M.A loblolly pine (Pinus taeda L.) karyotype has been developed based on fluorescent insitu hybridization (FISH) using cyto-molecular landmarks including plant telomere repeat, 18S-28S rDNA and 5S rDNA probes and DAPI positive bands. Somatic chromosome spreads of loblolly pine root tips were prepared using a modified enzymatic digestion technique. We observed ten pairs of long metacentric, one pair of long submetacentric and one pair of short sub-metacentric chromosomes. All the chromosomes showed characteristic DAPI positive bands (A-T rich regions) near and/or around the centromeres. At least one DAPI positive band was also observed in intercalary positions on all chromosome arms. Plant telomere FISH signals were observed towards the end of each chromosomal arm as expected. In addition, most of the chromosomes showed telomeric sites near and/or around the centromeres except for one or possibly two chromosomes. A total of seventeen 18S-28S rDNA sites were identified per haploid genome. Eight of these were located near and/or around the centromeres and seven were at intercalary positions. One major 5S rDNA site was observed in an intercalary region of a metacentric chromosome that lacked 18S-28S rDNA sites. One or possibly two minor 5S rDNA sites were observed near the ends of two different chromosomes. We are also developing a slash pine karyotype for direct comparison with loblolly as well as a comparison with a previously published slash karyotype (Doudrick et al. 1995, Journal of Heredity 86:289-296). Finally, we will provide an update on our progress toward using BAC clones as FISH probes on pine chromosomes.Item Molecular Pathology of Pitch Canker Disease(2003) Smith, K. E.; Morse, A. M.; Kayihan, G.; Huber, D. A.; White, T. L.; Nelson, C. D.; Davis, J. M.The inciting agent of pitch canker disease in Pinus species is the necrotrophic fungal pathogen Fusarium circinatum (teleomorph Gibberella circinata). Pitch canker disease has been identified in the southeastern United States, as well as in California, Mexico, Japan and South Africa. The disease is episodic in nature and can reach epidemic proportions with potentially devastating consequences for both managed and natural forests. Symptoms of pitch canker disease include discolored lesions (cankers) on stems and branches that generate profuse amounts of resin (pitch). Infected shoots eventually desiccate due to reduced water transport caused by pathogen development in vascular tissues. As with most diseases of pine, pitch canker disease is not well understood with respect to mechanisms of fungal pathogenicity, disease development, and disease resistance. To gain insight into the processes associated with disease development, we used a method called differential display of messenger RNA. This method was coupled with gene expression array analysis to identify genes from the pine host and from the fungal pathogen that are regulated differently during the disease state compared to the freeliving states of host and pathogen. The functions of these genes appear to be associated with plant defense and desiccation, however many genes of unknown function were also identified. The next goal of these studies is to identify genes that are associated with resistance, and to compare and contrast the gene expression programs that are associated with resistance vs. susceptibility. The large-scale screening of loblolly pine clones for resistance to pitch canker disease, which was carried out as part of the ADEPT project (Allele Discovery of Economically-important Pine Traits), is a major step toward this goal. Analysis of the screening study data revealed that resistance was heritable on the clone mean basis. A mixed linear model was used to predict genotypes that are highly resistant or highly susceptible to pitch canker disease. Ultimately it is hoped that association genetics approaches - such as those utilized in the ADEPT project - will identify host genes and alleles that condition pitch canker disease resistance. The genes identified by differential display serve as candidate genes for evaluating this approach.Item Representatives(2003)Item Registration List(2003)Item Evaluation of an Open-Nucleus Model for Forest Tree Breeding(2003) Lstiburek, M.; Mullin, T. J.Open-nucleus breeding was evaluated by stochastic simulation. Methodology was developed for unrestricted migration rate between two tiers (main and elite). Genetic progress in the breeding population was iteratively maximized for a wide range of restrictions on diversity varying from strong family selection to balanced within-family selection. The model assumed genetic parameters typical for growth traits in conifers and accounted for inbreeding depression. Comparison was made with a single population without hierarchical structure assuming constant testing effort. A seed orchard was established in each breeding cycle as a selected subset of the breeding population. The extra gain achieved by assigning better mates into the elite population was counteracted by increased group coancestry (relatedness) among seed orchard selections. The size of elite tier was found to have little importance in this study. When more effort was concentrated into elite crosses, potential for inbreeding in the seed orchard crop increased.