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Daniela Salvini, Silvia Fineschi, Roberta Pastorelli, Federico Sebastiani and Giovanni G. Vendramin

Twenty populations of the species aggregate Rubus fruticosus were collected throughout European natural forests and analyzed by chloroplast microsatellites (SSR). Results showed high genetic diversity (h T = 0.73) and haplotipic richness (17 haplotypes were detected), and the presence of several unique alleles. The value of genetic differentiation between populations was low for unordered alleles (G ST = 0.29) and for ordered alleles (N ST = 0.30), revealing the absence of phylogeographic structure of the haplotypic diversity. This can be mainly ascribed to the mechanisms of seed dispersal, mostly mediated by animal ingestion, which are responsible for a efficient gene flow through seeds. Rubus L. species are characterized by the ability to colonizing disturbed, but also intact forest communities, rapidly propagating though suckering and hybridizing with native species. Our results suggest that efficient seed dispersal can counterbalance the effects of vegetative propagation, maintaining a high genetic diversity.

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Diane Ragone

150 accessions of breadfruit [Artocarpus altilis (Parkinson) Fosberg and A. mariannensis Trècul] and interspecific hybrids from 18 Pacific island groups were analyzed for isozyme variation. Six enzyme systems (ACO, ADH, IDH, MDH, ME, PGM) produced well-resolved bands Each accession was scored for presence or absence of bands for each enzyme system. Breadfruit is clonally propagated and numerous diploid and triploid cultivars are grown in the Pacific islands. Diploid cultivars of A. altilis from Melanesia and western Polynesia showed the highest variation. Few diploid cultivars were found in eastern Polynesia. Seedless, triploid cultivars showed identical banding patterns for all enzyme systems. The narrow genetic variation in triploid cultivars indicates that they are the result of repeated vegetative propagation of a naturally occurring triploid. In contrast, these cultivars exhibit great morphological variation due to somatic mutation, maintained through human selection. A. mariannensis and hybrid cultivars showed greater variation and were identifiable by unique banding patterns for ADH and MDH.

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Diane Ragone

150 accessions of breadfruit [Artocarpus altilis (Parkinson) Fosberg and A. mariannensis Trècul] and interspecific hybrids from 18 Pacific island groups were analyzed for isozyme variation. Six enzyme systems (ACO, ADH, IDH, MDH, ME, PGM) produced well-resolved bands Each accession was scored for presence or absence of bands for each enzyme system. Breadfruit is clonally propagated and numerous diploid and triploid cultivars are grown in the Pacific islands. Diploid cultivars of A. altilis from Melanesia and western Polynesia showed the highest variation. Few diploid cultivars were found in eastern Polynesia. Seedless, triploid cultivars showed identical banding patterns for all enzyme systems. The narrow genetic variation in triploid cultivars indicates that they are the result of repeated vegetative propagation of a naturally occurring triploid. In contrast, these cultivars exhibit great morphological variation due to somatic mutation, maintained through human selection. A. mariannensis and hybrid cultivars showed greater variation and were identifiable by unique banding patterns for ADH and MDH.

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Steve McCulloch

Briggs Nurseries, Inc. has used micropropagation as method of vegetative propagation for over 20 years. Genetic stability and uniformity of plants that are produced and sold is of the utmost concern to the commercial plant propagator. Genetic stability may be accomplished by ensuring that all shoots formed in vitro are of axillary origin and by reducing shoot proliferation rates through the use of lower cytokinin concentrations in the culture medium. Excision and removal of callus during transfer is also necessary to ensure that shoots develop from axillary buds. Various factors that may influence genetic variability and its frequency of in vitro derived plants will be discussed with an emphasis on how to reduce them. Three sources of variation with tissue culture derived plants will also be reviewed (Swartz, 1991): a) source plant variability, b) genetic changes in vitro, and c) epigenetic or physiological adaptation.

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M.M. Jenderek, K.A. Schierenbeck and R.M. Hannan

Maintenance of garlic (A. sativum L.) germplasm collections is based on year-to-year vegetative propagation of individual accessions. Several accessions are phenotypically similar, often originating from the same region of the world, but have been collected by different people at different times. These accessions are currently maintained as separate and unique samples, but may represent genetic duplication in the collection. In order to identify genetic duplication in the USDA collection, 45 garlic Plant Introduction accessions from the garlic USDA germplasm collection were analyzed for RAPD marker polymorphism. The samples originated from 20 countries worldwide. RAPD bands were generated by 20 decamer primers, using 100-ng DNA template, and 38 PCR amplification cycles. Polymorphism between accessions was defined as presence or absence of particular bands at given loci. However, a few distinguishing RAPD markers were established for selected accessions, identifying additional molecular markers to wholly assess the similarities or polymorphism of the garlic collection units is necessary.

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Zhen-Xiang Lu, Gregory L. Reighard, Andrew P. Nyczepir, Thomas G. Beckman and David W. Ramming

Two F1 hybrid Prunus rootstocks, K62-68 and P101-41, developed from a cross of `Lovell' [susceptible to both Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood] and `Nemared' (resistant to both root-knot nematode species), were selfed to produce two F2 seedling populations. Vegetative propagation by herbaceous stem cuttings was used to produce four or eight self-rooted plants of each F2 seedling for treatment replications. Eggs of M. incognita and M. javanica were inoculated into the potted media where plants were transplanted, and plants were harvested and roots examined for signs and symptoms associated with root-knot nematode infection ≈120 days later. Segregation ratios in both F2 families suggested that resistance to M. incognita in `Nemared' is controlled by two dominant genes (Mi and Mij) and that to M. javanica by a single dominant gene (Mij). Thus, Mij conveys resistance to both M. incognita and M. javanica.

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David I. Yates, Brandi L. Earp, Foster Levy and Elaine S. Walker

To improve the success of vegetative propagation of Sciadopitys verticillata, stem cuttings were subjected to three treatments designed to minimize the accumulation of a latex-like sap at the cut ends of stems. A 24-hour soak in water before a hormone dip significantly enhanced rooting success and root mass. The water soak pretreatment was more beneficial to hardwood cuttings compared with softwood cuttings. Cuttings from shade-grown source trees showed the highest rooting success, but source tree age, height, and place of origin were not important factors. The water-insoluble latex-like sap had strong antibacterial activity against 3 of 11 bacterial species tested, but activity was not related to bacterial Gram reaction or the bacterial natural environment. In contrast, pine resins and latexes from selected angiosperms showed no antibacterial activity. The antibacterial component of the Sciadopitys latex-like sap was heat stable and therefore probably not protein based.

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Chieri Kubota, Haruna Maruko and Toyoki Kozai

For vegetative propagation of sweetpotato, single or multi-node leafy cuttings are used as propagules. A quantitative understanding of leaf development is important for predicting the number of propagules produced after a given production period under various environmental conditions. For plant production in a relatively closed structure, controlling CO2 concentration is necessary, but effects of CO2 concentration on cutting production rates of sweetpotato are not well-investigated. Single-node cuttings each with a fully expanded leaf (the initial leaf blade length was 66 mm) were grown under one of three levels of CO2 concentration (400, 800, and 1200 μmol·mol-1), 250 μmol·m-2·s-1 PPF, 16 h/day photoperiod, and 29 °C air temperature. The plant dry weight increased faster in the higher CO2 concentrations. Changes in the number of harvestable cuttings during the production period was defined by changes in the number of leaves reaching a leaf blade length (LBL) longer than a given standard length (LS). The number of harvestable cuttings increased almost linearly with time after the LBL of the first leaf reached the LS, regardless of CO2 concentration. The effect of CO2 concentration on cutting production rate (number of harvestable cuttings per day) was varied with different LS. For example, at LS = 20, 30, and 40 mm, the cutting production rate increased slightly at higher CO2 concentrations, while at LS = 60 mm, it decreased significantly at higher CO2 concentrations. This indicates that, under the present experimental conditions, increasing CO2 concentration increased the number of small leaves that might not be usable as cuttings (propagules). Environmental control is necessary in vegetative propagation to increase the number of propagules and the biomass usable as propagules, thereby minimizing energy and resources needed for the propagule/transplant production process.

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Jennifer A. Gargiulo and Michael E. Kane

The genus Cryptocoryne (Araceae) contains some of the most commercially important amphibious species used in the aquarium plant trade. However, seed production is rare and vegetative propagation by rhizome division is extremely slow. Procedures for in vitro establishment, axillary shoot proliferation and plantlet acclimatization of Cryptocoryne Becketti Thwaites ex Trimen were determined. Surface sterilized rhizomatous shoot tips were established on a medium consisting of Linsmaier & Skoog mineral salts and organics supplemented with 87.6 mM sucrose, 2.2 μM benzyladenine (BA) and 0.57 μM indole-3-acetic acid (IAA) solidified with 0.8% TC® Agar. Effects of medium supplementation with factorial combinations of BA (0 - 25 μM) and IAA (0 - 10 μM) on axillary shoot proliferation from single node explants were determined after 28 days. Maximum axillary shoot proliferation (`l-fold increase) occurred on medium supplemented with 25 μM BA and 1.0 μM IAA. Excellent microcutting rooting (100%) was achieved by direct sticking in Vergro Klay Mix A. Greenhouse acclimatization of rooted microcuttings was 100%.

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S.C. Myers and A.T. Savelle

`Guardian' peach rootstock has shown improved survivability in areas where root-knot nematode and peach tree short life are a problem. Many peach rootstocks are typically propagated from seed. Availability of seed may vary and the long-term genetic uniformity of rootstock material may be difficult to maintain due to out-crossing during seed production. A reliable, successful vegetative propagation method would potentially increase the rate at which material could be made available and more closely ensure genetic uniformity. Production of liners was compared between rooted cuttings and seed of mature `Guardian', `Lovell', and `Nemaguard' peach trees. Seed were stratified under uniform conditions, planted at initial germination, and seedling emergence recorded 30 days after planting. Terminal softwood and semi-hardwood cutting were treated with KIBA and rooted under intermittent mist in a greenhouse. Rooting percentage was equal to or greater than percent seedling emergence. Optimum results were obtained with semi-hardwood cuttings taken in July and August. Rooted cuttings transplanted to the field produced liners of equal or greater quality than liners produced from seed. Seedlings exhibited variability in growth in the nursery area. Rooted cuttings had fewer lateral branches in the lower 15 cm of rootstock where trees were T-budded with certified, virus-indexed buds of `Cresthaven' peach.