has a detrimental impact in Hawaii on both commercial production and germplasm conservation. Although tolerance but not genetic resistance to PRSV has been reported in the Carica germplasm, PRSV-resistant plants have been achieved by genetic
Tracie K. Matsumoto, Francis T.P. Zee, Jon Y. Suzuki, Savarni Tripathi, James Carr, and Bruce Mackey
Boling Liu, Hongzhou Fang, Chaorong Meng, Ming Chen, Qingdong Chai, Kai Zhang, and Shijuan Liu
with lines, which are known as the window-leaved plants ( Krulik, 1980 ). Thus, this micropropagation protocol could facilitate in the propagation of H. turgida for commercial cultivation, as well as germplasm conservation. Literature Cited Amoo, S
Angela Baldo, Larry Robertson, and Joanne Labate
Cultivated tomato varieties are genetically extremely similar. We identified 764 Unigenes with potential single nucleotide polymorphisms (SNPs) among more than 15 cultivars from public expressed tomato data. By sequencing regions from 53 of these Unigenes in two to three cultivars, we discovered an unexpected wealth of nucleotide polymorphism (62 SNPs and 12 indels in 21 Unigenes). This included a high proportion of predicted nonsynonymous nucleotide (17 of 33 SNPs in exons) and nonconservative amino acid (6 of 16 nonsynonymous SNPs) changes. We hypothesize that five of these regions are associated with introgressions from wild relatives. Identifying polymorphic, expressed genes in the tomato genome will be useful for both tomato improvement and germplasm conservation.
Antonieta N. Salomão and Rosângela C. Mundim
The effects on germination of two lots of Carica papaya seed of dehydration at 25 °C, followed by exposure to -20 °C or -196 °C, were evaluated with and without gibberellic acid (GA3) treatment. In the absence of GA3 treatment, dehydration increased subsequent germination only in seed lot 1 when moisture content (m.c.) was reduced from 59% to 6.0% and 5.3%. In seed lot 2, dehydration followed by exposure to -196 °C increased germination compared with dehydration alone. Treatment with GA3 enhanced germination rate in all treatments. Dehydration to 5.3% (lot 1) or 6.9% and 6.8% m.c. (lot 2), followed by exposure to subzero temperatures and treatment with GA3, were the most favorable combined treatments to enhance papaya seed germination. The results suggest that papaya seed presents an orthodox behavior, permitting germplasm conservation in conventional and cryogenic genebanks.
Don J. Durzan and M.D. Durzan
Prospects for the establishment of joint-ventured agribusiness in developing countries are a function of international agreements, local risk conditions, business networks, and banking systems that are willing to support the innovative transfer, protection, assessment, and commercialization of biotechnology. The integration of biotechnology will occur only if truly convincing practices emerge that enhance biodiversity and the competitiveness of sustainable production, utilization, and marketing cycles. Integration also depends on agreements on intellectual property rights, plant protection, trade and tariffs, price stabilization, and non-trade-distorting policies. These policies deal with broad issues in research, pest and disease control, environmental quality, germplasm conservation, resource retirement programs, and even with crop and disaster insurance. Measures derived from these policies will apply to novel processes and to organisms that have been genetically engineered and approved for release into the environment. For developing countries, much more attention will have to be paid to biological diversity and sustainable balances among intercropped agriforest and horticultural production systems. Balances should be compatible with regional and local customs and practices before genetically engineered “green goods and services” are introduced in the marketplace. Recombinant DNA technologies are currently better-suited to deal on a “gene-by-gene” basis, with commodity surpluses and material conversions involving more concentrated and industrialized processes than with field plantations of genetically engineered, complex, and long-lived crops that may require considerable adaptive plasticity. In most countries with developing economies, the integration of recombinant DNA technology represents a “special problematique” involving politico- and socioeconomic and environmental factors. Barriers to transfer and integration may involve evolving international agreements, public acceptance, resource over-exploitation, environmental degradation, rapid insect and disease resistance, contaminated water and food supplies, reduced quality of life, labor quality, corruption, crime, farmers' rights, germplasm conservation, and lack of protection of intellectual property, among other factors. Hence, the timing and mode of transferring biotechnology needs considerable impact assessment on a case-by-case basis.
Mario Crespo, James Nienhuis, Jan Tivang, and Paul Skroch
Knowledge of relative genetic distance among genotypes is useful in a breeding program because it permits organization of germplasm resources. Genetic distance (GD) was estimated among 113 faba bean, Vicia faba L. genotypes, which included three botanical varieties from different geographical areas around the world. The genotypes included 87 accessions from Bolivia, 14 accessions from the Middle East and North Africa, five accessions from Australia, and seven commercial varieties from Europe. Twenty-three RAPD primers were scored yielding four to 13 polymorphic bands resulting in a total of 165 bands. Our objective was to determine genetic relationships among accessions and cultivars as measured by RAPD markers. The genetic relationships were estimated using the ratio of discordant to total bands scored. A multidimensional scaling (MDS) plot indicated four clusters corresponding to: i) European commercial cultivars; ii) the Middle East, North Africa, and Australian accessions; iii) the Bolivian highland landraces; and iv) the Bolivian collection maintained in a valley environment. A permutation test confirmed the four clusters (P < 0.01). Sampling variance results indicated that a CV of 10% could be obtained with as few as 148 bands between groups. Selection and drift appears the main cause of divergence of two populations in the Bolivian faba bean collection. The results of this study indicated that RAPDs are a powerful tool for evaluation of germplasm conservation methods in faba bean.
E.J. Sacks and D.A. St. Clair
We have developed a method for cryopreserving Lycopersicon esculentum pollen to facilitate the timing of crosses and for long-term germplasm conservation. Gelatin capsules containing pollen were wrapped in tissue paper and placed in air-tight glass tubes with anhydrous calcium sulfate desiccant. Tubes containing pollen were stored at –80C. In one experiment, we stored the pollen of LA359 and T5 at –80C for 37 days. Pollen predesiccated overnight at 4C then stored at –80C, pollen put in a tube with desiccant then immediately stored at –80C, and fresh pollen were compared by pollinating 10 flowers of LA359 with each of the six pollen treatments and counting the number of seed per fruit. Average seed counts ranged from 127 for fresh, T5 pollen to 172 for predesiccated LA359 pollen. In another experiment, cryopreserved pollen of UC82B and VFNT Cherry was given from 0 to 6 cycles of freezing and thawing. Ten flowers of LA359 were pollinated with each of the 12 treatments. Average seed counts ranged from 125 to 152. The data from both experiments suggest that cryopreservation of tomato pollen to facilitate efficient plant breeding is feasible.
Anfu Hou, James R. McFerson, and Warren F. Lamboy
Molecular DNA markers based on the RAPD (random amplified polymorphic DNA) assay are gaining use in germplasm assessment. RAPD markers are simple, relatively inexpensive, and highly informative. We used five primers to assess 26 Brassica oleracea breeding lines from the IVF and nine accessions from the PGRU. The test array included eight subspecies of B. oleracea. We generated 90 RAPD markers and were able to unambiguously discriminate among all 35 test entries, but could not separate subspecies within B. oleracea. Genetic similarity between subspecies ranged from 0.629 to 0.738. Average similarity within accessions was 0.96, confirming the suspected homogeneity of breeding lines. Nevertheless, significant genetic diversity was found among kohlrabi, broccoli, and cabbage accessions. Similarity analysis of breeding lines and hybrids confirmed their pedigree relationships. Interestingly, B. o. subsp. costata `Couve Nabica' showed closer similarity to B. napus subsp. oleifera `Jet Neuf' than to other B. o. materials and B. o. subsp. italica `Packman' showed higher similarity to some cabbages than to other broccolis. Results provide further evidence that diversity assessment using RAPDs is broadly applicable and useful in germplasm conservation and utilization.
Hongwen Huang and Desmond R. Layne
The pawpaw is the largest tree fruit native to the United States and the only temperate member of the tropical Custard Apple family (Annonaceae). In 1995, Kentucky State Univ. was established as the USDA-ARS-National Clonal Germplasm Repository for Asimina spp. Seedling trees from 400 pawpaw accessions representing 70 distinct geographic regions from 17 states are currently being grown at our research farm. In a preliminary study, 18 pawpaw cultivars were assayed in 30 enzyme systems using an isoelectric focusing polyacrylamide slab gel system of pH 4-9. Twelve enzymes produced high resolution without tissue specificity and were further used for evaluation of allozyme diversity of geographic populations. Degree of genetic diversity within populations and differentiation between populations as evaluated by the expected heterozygosity (He), the proportion of polymorphic loci (P), the average number of alleles per locus (A), chi-squared analysis of allele frequency heterogeneity, Nei's standard genetic distance (D), and identity (I) will be discussed. Dendrograms were generated by cluster analysis using the unweighted pair group method to demonstrate the relationships of geographic populations in the 17 states evaluated. The strategy for germplasm conservation and cultivar development through breeding will also be discussed.
Hongmei Ma and Margaret Pooler
Ornamental flowering cherry trees (Prunus species) are popular landscape plants that are used in residential and commercial landscapes throughout most temperate regions of the world. Most of the flowering cherry trees planted in the United States represent relatively few species. The U.S. National Arboretum has an ongoing breeding program aimed at broadening this base by developing new cultivars of ornamental cherry with disease and pest resistance, tolerance to environmental stresses, and superior ornamental characteristics. Knowledge of the genetic relationships among species would be useful in breeding and germplasm conservation efforts. However, the taxonomy of flowering cherry species and cultivars is complicated by differences in ploidy levels and intercrossing among species. We have used simple sequence repeat (SSR) markers developed for other Prunus species to screen a diverse collection of over 200 ornamental cherry genotypes representing 70 taxa in order to determine the genetic relationships among species, cultivars, and accessions. Data were generated from 9–12 primer pairs using an automated DNA genetic analyzer (ABI3770), and subjected to UPGMA cluster analysis. Extremely high levels of polymorphism were exhibited among the materials studied, thus indicating that ornamental flowering cherry germplasm has substantial inherent genetic diversity. This information, combined with traditional morphological characteristics, will be useful in determining genetic relationships among accessions in our collection and for predicting crossability of taxa.