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T. P. Straathof and R. G. Goldy

Abstract

Seed from three octoploid (2n = 8x = 56) Fragaria species [F. × ananassa Duch., F. chiloensis (L.) Duch., and F. virginiana Duch.] and three diploid (2n = 2x = 14) species (F. vesca L., F. viridis Duch., and F. daltoniana J. Gay) were placed in vitro on water agar (WA) and ex vitro on 1 sand : 1 sphagnum (v/v) mix. Seed of the octoploid species germinated best regardless of medium. Octoploid species also exhibited better establishment on modified Boxus proliferation medium than the diploids. Five in vitro germination media were tested for F. vesca and F. × ananassa. Fragaria × ananassa germinated best when WA, or WA + sucrose (Su) + 0.1, or 0.05 strength Boxus proliferation nutrients (Nu) was used as the germination medium. Fragaria vesca showed no difference in germination on Su or Nu. However, establishment of F. vesca on proliferation medium was improved if Nu was included in the germination medium. Data indicated that selection for diploid genotypes with good in vitro establishment is possible.

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Ing-Jiun Tom Wu, G.L. Wheeler, and F.H. Huang

Scarification treatments (a control, a 10-minute vacuum, or a 1.5-minute ultrasound), different media (modified Norstog and Van Waes) and growth regulators [benzyladenine (BA) at 0, 1, 1.5, or 2 mg·L-1 and 6-(r,r-dimethylallylamino)-purine riboside (2iPR) at 0, 1, 1.5 or 2 mg·L-1] were used in combination to increase seed germination of Cypripedium calceolus var. parviflorum. Seeds treated with ultrasound had higher germination (58.0%) than those treated with vacuum (27.4%) or controls (19.2%). Germination rates increased with 2iPR level and reached a maximum between 1.5 and 2 mg·L-1. Seeds on Van Waes medium, which were not transferred to fresh medium after germination, had a severe browning problem causing many protocorms to die. Those on Norstog medium continued to grow into seedlings with less browning. Germination rates of Calopogon tuberosus × Calopogon `Adventure' and Liparis liliifolia were determined on the different media and growth regulator treatments. Multiple shoots of Calopogon developed from single seeds on media containing growth regulators. Flower buds formed in vitro on Calopogon in media containing 1 mg·L-1 or higher BA 5 months after germination. L. Iiliifolia seeds in Norstog medium had a higher proportion of germination than those in Van Waes medium.

Open access

G. E. Short, R. Loria, and M. L. Lacy

Abstract

‘Miragreen’ garden pea seeds from individual seed lots were sorted into bleached, partially-bleached, and non-bleached categories. Seeds were either soaked for 48 hours in aerated water at 22°C, coated with thiram fungicide, or received no treatment. Seeds were planted in Conover loam soil where damping-off and seedling rot were primarily caused by Pythium ultimum Trow and Fusarium solani (Mort.) Sacc f. sp. pisi (Jones) Snyd. & Hans. No differences in germination in vitro were found among bleached, partially bleached, and non-bleached seeds. However, seedling emergence in the field was greater from untreated non-bleached seeds (69%) than from untreated bleached seeds (30%); emergence from partially bleached seeds (58%) was intermediate. Regardless of degree of bleaching, all seedlings were a normal green color after emergence, and appeared equal in vigor. Pea yields from untreated bleached seeds were less than from untreated non-bleached seeds, apparently because pea-emergence damping off was so much greater with bleached than with non-bleached seeds. No yield differences occurred with fungicide-treated seeds. Soaking partially bleached seeds for 48 hours in aerated water at 22°C prior to planting in April was as effective in improving emergence in artificially infested soil as coating seeds with thiram. However, when seeds were planted in mid-June, the thiram treatment gave higher seedling emergence than the soaking treatment. In general, high yields were achieved by early planting of seeds and minimum root rot.

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Marìa Andrade-Rodrìguez, Angel Villegas-Monter, and M. Alejandra Gutièrrez-Espinosa

Polyembryony is an important characteristic for citrus that allows them to be propagated clonally through seed. Even when it is genetically controlled by a quantitative trait, the environment in which the seed is developed can affect it. The aims of this investigation were to evaluate polyembriony in two citric rootstocks in two harvest cycles and embryo germination of polyembrionic seeds. Embryos of 300 seeds of Citrus volkameriana and C. amblycarpa were counted and measured in Summer-Fall and Winter 1998 and 1999, respectively; embryo of 50 seeds of both rootstocks were germinated in vitro. The number of embryos per seed was 1.9 and 1.6 in C. volkameriana and 4.7 and 5.7 in C. amblycarpa. In C. volkameriana, we observed 42% of monoembryonic seeds during summer-fall and 67% in winter, whereas in C. amblycarpa 5.0 and 4.1% were detected, respectively. Only embryos that were larger than 1 mm long germinated. Even when germination takes similar time (5 to 6 days), further growth is faster in larger embryos (5 to 10 mm) than smaller ones. Therefore, size of embryos would need to be considered for propagation purposes.

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S. Kukkurainen, A. Leino, S. Vähämiko, H.R. Kärkkäinen, K. Ahanen, S. Sorvari, R. Rugienius, and O. Toldi

The occurrence of bacteria in different tissues was studied using field-grown strawberries, in vitro-grown strawberries, wild strawberries, and aseptically germinated strawberry seedlings. Strawberry has a number of endophytic bacteria in its the internal tissue, most of which appear to be nonpathogenic. In the in vitro-grown strawberries, all identified isolates were in the genus Pantoea. In field-grown garden and wild strawberries the most common genera were Pantoea and Pseudomonas. Location of eubacterial inhabitants within strawberry tissue sections was studied by in situ hybridization. Bacteria were detected in flower stalks, leaf stalks, leaves, stolons, berries and aseptically germinated seedlings. The existence of bacteria in seeds and seedlings suggests that bacteria are able to move up to the generative tissue and, ultimately, to the next generation, forming a symbiosis-like chain of plant-bacteria coexistence.

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M. L. Meyer and F. A. Bliss

Kiwifruit (Actinidia deliciosa) is a functionally dioecious plant where fruit size is dependent on number of seeds set. Pollen fertility was estimated in 1990 and 1991 by percentage stainability and percentage germinability in vitro. Profiles of the isozymes AAT, GPI and PGM were used to assess if any large differences in pollen fertility could be attributed to genotypic variation. Based on these three isozymes, eight different genotypes were discovered. Although significant differences were found among vines within orchards and among orchards, all vines can be considered good pollenizers (stainability > 87%). A positive correlation was found in 1991 between percentage stainability and percentage germination.

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M.R. Pooler and R. Scorza

publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.

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Charlotte R. Chan and Robert D. Marquard

The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.

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Michael J. Tanabe and Nicole Wakida

Noni, Morinda citrifolia, is receiving a lot of attention for its potential medicinal effects. Hawaii is an ideal growing environment for this plant, where it has been used for many purposes, including medicinal ones, by ancient Polynesians. Currently, there is a rapidly developing noni industry in the state of Hawaii. Propagation of this plant is almost exclusively by seeds, and germination generally requires a couple of months without preconditioning or about a month if mechanically scarified. We developed an in vitro protocol that significantly improves percent germination rate by altering incubation temperature and the in vitro culture basal medium. Germination time was decreased to 4 days when the embryo was extracted and exposed to 31 °C. A basal medium containing 1/2 Murashige and Skoog (M&S) salts was the most effective in reducing germination time and increasing percent germination. Stem pieces obtained from in vitro-propagated seedlings produced callus when explanted in 1/2 M&S containing various levels of naphthalene acetic acid (NAA). The most effective treatment was 0.5 μm NAA and the least effective treatment was 2 μm NAA. Treatments without NAA did not produce callus. Calli treated with 4.40 μm 6-benzylaminopurine (BA) or 8.80 μm BA were the most effective in promoting caulogenesis. We also demonstrated that the number of first generation seedlings produced from each embryo could be increased by treatment with 8.80 μm BA.

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Michael E. Compton

Several methods have been published on shoot regeneration from watermelon cotyledon explants. The major differences in regeneration protocols include the light environment in which seeds are germinated and the cotyledon region used. The purpose of these experiments was to compare the two main protocols for plant regeneration and develop one general procedure. To fulfill this objective, seeds were germinated in vitro in darkness or 16-hr light photoperiod for 7 days. Cotyledon explants from four watermelon cultivars (`Crimson Sweet', `Minilee', `Sweet Gem', and `Yellow Doll') were prepared from both dark- and light-grown seedlings. Apical and basal halves were obtained by making a cut across the cotyledon width. Apical and basal quarters were made, for comparison, by cutting apical and basal halves longitudinally. All explants were incubated on shoot regeneration medium for 6 weeks followed by a 3-week cycle on shoot elonga-tion medium. The percentage of cotyledons with shoots was 1.7-fold greater for cotyledons derived from seedings incubated in darkness than those germinated in light. Shoot formation was about 10-fold greater for explants from cotyledon basal halves and quarters than apical halves and quarters. According to these results, the best watermelon regeneration protocol should consists of basal explants from in vitro-germinated seedlings incubated in the dark for 7 days.