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  • Author or Editor: Harrison Hughes x
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Incomplete vascular connection between roots and shoots of various in vitro plantlets has been implicated in the poor survival of acclimatized plants. In this study, the anatomy of the stem-root transition region of in vitro and acclimatized grape (Vitis sp.`Valiant') were studied by light microscopy. Grape plantlets were micropropagated on MS medium supplemented with 5μM BAP for multiplication and 0.4 μM NAA for rooting. Roots developed directly from stem tissues after two weeks in rooting media. Subsequently in vitro rooted plantlets were acclimatized in the greenhouse for 6 weeks. Continuation of xylem vessels were observed in the stem-root transition region of the in vitro plantlets. No anatomical differences were observed in stem-root transition regions between direct rooting in vitro and those acclimatized ex-vitro for 6 weeks. Therefore, poor survival of in vitro propagated grapes are not due to incomplete vascular connection between roots and shoots.

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Isozymes have been used since the 1960's to identify species and cultivars in many different genera in the plant and animal kingdom. Each species has a unique banding pattern for its various isozymes with the number of detectable isozymes dependent on factors such as the number of genes coding for the enzyme, the number of alleles of each gene, the quarternary structure of the enzyme and the possible formation of intergenic enzymes. Alstroemeria is an important cut flower currently ranked 4th in production in the U.S. The cultivars that are available to the growers have largely been developed in England and the Netherlands. The origin of these cultivars has not been well documented. As a consequence, cultivar development in the U.S. cannot easily resynthesize new cultivars from the original parents used in Europe. We are currently using isozymes to characterize some of the species which are thought to have been the progenitors of the commercial hybrids. These isozyme systems are then used to screen available hybrids for determination of the parental origin of the hybrids. This information could be used to narrow the choice of parents to be used in a breeding program for the development of the U.S. hybrids.

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Abstract

Callus from salpiglossis anthers was derived from sporophytic tissue and differentiated into flowering plantlets in vitro.

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Abstract

Octoploid strawberry, Fragaria × ananassa Duch., (2n = 56), pollinated by Potentilla anserina L. (2n = 28) and P. fruticosa L. cv. Golddrop (2n = 14) gave high achene set but germination was low and seedling lethality high in both cases. Most offspring from P. anserina died by 6 weeks with 1% survival of germinating seed at 34 weeks; offspring from P. fruticosa pollination showed gradual mortality with 7% surviving at 34 weeks. Surviving offspring from P. anserina pollinations were either 28 chromosome tetrahaploids (5 plants) or 56 chromosome octoploids (4 plants). Surviving offspring from P. fruticosa pollinations included tetrahaploids (2 plants), octoploid (1 plant), or 35-chromosome pentaploid intergeneric hybrids (9 plants). Tetrahaploids are weak with small leaves and two that have flowered are pollen and pistil sterile.

Open Access

Propagation of Winecups [Callirhoe involucrata (Torrey & A. Gray)] for use as a landscape ornamental has been impeded by a lack of understanding of the seed dormancy and a practical method for overcoming it. As with many members of the Malvaceae family, C. involucrata produces hard seed. In the populations tested, it accounted for 90% of an average sample. Impermeability, however, is not the only limiting factor to germination. Three disparate populations of seed, representing two different collection years have been investigated using moist pre-chilling, boiling water, leaching, gibberellic acid, hydrogen peroxide and mechanical and chemical scarification methods. Scarifying in concentrated sulfuric acid stimulates germination of some seed fractions and causes embryonic damage in others, suggesting variation in seed coat thickness. Similar results were obtained using a pressurized air-scarifier; the hard seed coat of some seed fractions were precisely scarified while others were physically damaged using the same psi/time treatment. Placing seed in boiling water increases germination from 4%, 7%, and 18 % to 23%, 25%, and 77% in the three populations, respectively. Leaching for 24/48 h in cold (18 °C) aerated water or for 24 h in warm (40 °C) aerated water showed only a minor increase over the control. Pre-chilling at 5 °C for 30, 60, and 90 days showed no improvement over the control. Gibberellic acid-soaked blotters improved germination at 400 ppm to 20%, 10%, and 41%; at 500 ppm germination was reduced. Soaking seed for 24 h in a 3% concentration of hydrogen peroxide did not effect germination; at a 30% concentration germination was reduced. The considerable variation in seed dormancy expression may be a function of differences in environmental factors during development or seed age.

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Fringed gentian, Gentiana thermalis (O. Kuntze) Iltis is an attractive wildflower, that may be used as a fall flowering ornamental. This species has received limited attention in terms of seed viability and germination. Seeds were subjected to a tetrazolium viability test that involved imbibition for 24 hours at 22C. No embryos in any line tested were stained. However, imbibition at 3C for up to 4 weeks followed by staining at 22C resulted in significant levels of positive viability, as indicated by embryo staining. A germination study indicated that stratification was necessary for germination, with 6 weeks chilling giving better results than 0 or 3 weeks. However, the number of seeds germinated was less than expected, given the results of the tetrazolium test.

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Freezing is the major abiotic stress that limits geographic distribution of warm season turfgrasses. Prior studies have indicated variation in freezing tolerance in saltgrass clones. Therefore, this study examined freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these clones were evaluated for time of leaf browning in the fall with the intent to determine if there was a correlation between this trait and freezing tolerance. Rhizomes were sampled during 2004 and 2005 midwinters from clones established in Fort Collins, Colo., and then subjected to a freezing test in a programmable freezer. Saltgrass freezing tolerance was highly influenced by the climatic zone of clone origin in both years of the experiment. Clones with greater freezing tolerance turned brown earlier in fall in both seasons. Ranking of zones for the average LT50 (lethal temperature at which 50% of rhizomes died) was: zone 4, most northern (−17.2 °C) < zone 5 (−14.4 °C), < zone 6, most southern (−11.1 °C) in 2004, and zone 4 (−18.3 °C), < zone 5 (−15.7 °C) < zone 6 (−13.1 °C) in 2005. Clones from northern areas tolerated lower freezing temperatures overall. This likely indicates that freezing tolerance is inherited. Large intraspecific variation in freezing tolerance may be effectively used in developing cold hardy cultivars.

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Previous studies have shown that liquid medium additions on established cultures enhance shoot growth and proliferation. In the present report, the growth and multiplication of apples and grapes were evaluated after the addition of liquid media to established cultures. Grapes and apples were micropropagated on agar solidified nutrient medium with 5μM BAP, and 4.4μM BAP, 1.4μM GA, 4.9μM IBA, respectively. A liquid overlay of similar medium was added after 4 to 6 weeks in both cultures. Improved growth, number of shoots, and a reduction in callus growth were observed in both species as compared to shoots transferred to fresh solid media. The number of micropropagated apple shoots and their height increased significantly by 35% and 69% respectively. Proliferation of grape shoots increased by 198% while callus growth decreased by 64% when compared to cultures transferred to fresh solid media.

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After 6 months of growth in 200,400, and 500 mm NaCl, cultured cells of Distichlis spicata showed a decreased cell volume (size) despite maintenance of turgor pressure sometimes 2-fold higher than that of the control. Tensile strength, as measured by a nitrogen gas decompression technique, showed empirically that the walls of NaCl-stressed cells were weaker than those of nonstressed cells. Breaking pressures of the walls of control cells were ≈68 ± 4 bars, while that of the walls of cells grown in 500 mm NaCl (-25 bars) were 14 ± 2 bars. The relative amount of cellulose per cell remained about constant despite salt stress. However, glucuronoarabinoxylans were more readily extractable, presumably because of a decrease in cross-linkage with phenol substances. Therefore, we suggest that cellulose microfibrils are not the only determinants that confer tensile strength to the primary cell wall, but rather subtle changes in the matrix polysaccharides are likely responsible for this event.

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Stevia (Stevia rebaudiana Bert.) leaves produce stevioside and rebaudioside that can be used as a natural source of low-calorie sweetener which is heat-stable. Because of low fertility, this plant is often vegetatively propagated for field production. This study was conducted to optimize tissue culture procedures for propagating selected clones and explore the feasibility of producing the sweetener compounds by callus cultures. Shoot proliferation was best in Murashige and Skoog (MS) medium supplemented with 0.1 mg/l naphthaleneacetic acid (NAA) Plus 10 mg/l kinetin. Kinetin as a cytokinin source was better than benzyladenine (BA) especially when NAA was present. Callus production fronm leaf disc cultures was most prolific when a combination of 0.1 mg/l NAA and 3 mg/l BA was used in MS medium. The relative sweetener contents of callus cultures are currently being-analyzed.

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