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Abstract

A phenotypic and sexual analysis of Fragaria vesca ‘Albo-Marginata’ determined that the leaf variegation was of chimeral origin. Stable periclinal chimeras were established in vitro from runner tips. Plants were transferred to proliferation media containing 0.5 μm IBA, 0.3 μm GA3, and BA at either 0, 1.3, 4.4, or 13.2 μm. Whereas the histogens of field-grown runner plants remained stable, more than 90% of the plantlets propagated in vitro varied from the original explants. Most variants were albino or were green, but some were mericlinal chimeras. Histological evidence indicated that many shoots were adventitious, arising from basal callus tissue or petioles. Chemical names used: 1H-indole-3-butanoic acid (IBA); gibberellic acid (GA3); N-(phenylmethyl)-1H-purin-6-amine (BA).

Open Access

Effects of heat stress on viable and nonviable axillary meristem development and subsequent lateral branching in 'Improved Mefo' chrysanthemum [Dendranthema ×grandiflorum Ramat. (Kitamura)] were studied. Plants grown at 33 °C day/27 °C night produced more nonviable buds than did plants grown at 23 °C day/18 °C night. A negative linear relationship {y = 28.7 + [-0.66 (x days)], r 2 = 0.70} between timing of exposure to high temperatures and the number of nonviable buds was observed. Histological examination 28 days after exposure to 33 °C/27 °C revealed that plants showed both normal and abnormal bud development. Abnormal bud development occurred as a consequence of premature differentiation of axillary meristematic tissue into nonmeristematic parenchyma tissue immediately after separation of axillary from apical meristems.

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The relationship between cell division, nonstructural carbohydrates and fruit size was investigated using 5-year-old `Encore' peach [Prunus persica (L.) Batsch]. The trees, which were trained to two opposing scaffolds, were selected for uniformity based on tree size and floral bud density. One-year-old shoots ranging in size from 20 to 30 cm were tagged from throughout the canopy. At anthesis, one entire scaffold was thinned of 75% of its flowers, leaving 25% in the mid-section of each shoot. The opposing scaffold served as the control. Samples were taken at three intervals for histological analysis: Anthesis, 30 days, and 45 days after full bloom. Nonstructural carbohydrates were analyzed on samples taken at five intervals: Anthesis, 10, 20, 30, and 45 days after full bloom. Volumetric size increased 29% by 30 days after full bloom, and 64% by 45 days after full bloom. Final fruit size (volumetric) was increased 8% by harvest.

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Two lines of tabasco pepper (Capsicum frutescens) were previously identified that differ significantly in ease of fruit detachment force. Greenhouse-grown plants of these lines, `McIlhenny Select' and `HP', were investigated for differences in cell organization in the fruit-receptacle area and the separation zone at different developmental stages. Histological examination indicated that fruit of `HP', which requires greater force to separate, exhibited a larger region of sclerified cells within the fruit-receptacle area. In contrast, fruit of `McIlhenny Select', the line that detaches easier, had fewer sclerified cells in this region. Cell sclerification increased for both lines with increasing fruit maturity. The fruit-pedicel separation zone in both lines is distal to the sclerified region and is composed of parenchymatous fruit tissue. The separation zone for `HP' includes at least 10 additional distal cell layers in the fruit septal region than `McIlhenny Select'.

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Propagation of Curcuma roscoeana in vitro was done successfully by culturing 0.5 × 1.0 mm shoot tips from young buds onto modified MS (1962) + 0.25 mg·L–1 kinetin. The bud-derived new plantlets could be multiplied on a new medium. Stem explants 10 mm in size, measured from base of the plantlets longitudinally cut in half, were the most suitable culture explants providing 2.8 new healthy plantlets/cultured explant. Explants from 4, 6, and 8 weeks old plantlets were more suitable than those of 2 weeks old when grown on agar or in liquid medium. From a histological study, it was found that new buds developed from preexisting meristems. The buds, like root initiation, could also occur directly from initial culture explants, not through callus. The plantlets obtained could successfully be transferred into growing pots, having a 95% survival rate.

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Development of Cornus florida L. pollen was monitored using standard paraffin histological techniques and light microscopy. Terminal buds (putative floral buds) were collected over a 6 weeks from mature landscape trees located on The Univ. of Tennessee Agricultural Campus, Knoxville. Examination of samples taken at 3- to 7-day intervals revealed variations in development representing 1- to 2-week differences between florets in a single inflorescence, florets on the same tree, and florets from different trees. Floral initiation occurred before 19 July in the 2 years of this study. Pollen development followed typical angiosperm stages: tapetal cells were multinucleate, pollen tetrads were tetrahedral, and meiosis occurred late in the developmental period. Pollen grains appeared morphologically mature by early September in both years.

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Dissected white ash seeds were placed on a MS basal medium containing 10 μM TDZ and 1 μM 2,4-D. Adventitious buds formed directly and indirectly on cotyledons and hypocotyls that were in contact with the medium. Histological observations after 7 days from initiation indicated early divisional events originated directly in subepidermal layers on adaxial portions of the cotyledons. As these cells divided, the growth ruptured the epidermis. Bud-like structures were seen at 3 weeks. After transfer to a secondary medium containing 3 μM TDZ, 1 μM BA, and 1 μM IBA, some of adventitious buds elongated. Efforts (gibberellin, etiolation, ABA, and silver nitrate treatments) to increase the number of elongated buds have been unsuccessful. Excised adventitious shoots were rooted under mist and established in the greenhouse.

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-28-0097. We gratefully appreciate the assistance of Raoul Machiavelli with statistical analyses and the technical assistance of Cheryl Crowder and the staff of the Louisiana State Univ. Veterinary School Histology Laboratory, Baton Rouge. Appreciation is also

Free access

Abstract

Uniform, actively growing apple seedlings, 10-15 cm high, were sprayed with 1000 ppm succinamic acid 2-2 dimethyl hydrazide (Alar). The apical portion of treated and control seedlings was collected at the following intervals after treatment: 3, 27 hr; 3, 6, 8, 14 days; 5 weeks. Sections through the apex were prepared, stained and examined microscopically for mitotic figures. As compared with controls, the frequency of mitotic figures in the stem apex of treated plants progressively decreased through 3 days, thereafter the number of figures increased to 69% of that in untreated plants on the 14th day. In the rib meristem frequency of mitosis declined slightly at 3 hr, then progressively until the 3rd day, after which the number of figures increased progressively to the 14th day when it was 28% of that in untreated plants. Only a temporary decrease in mitotic activity occurred in young leaf primordia during the first 6 days. Five weeks old treated seedlings were examined for histological abnormalities associated with extreme shortening of internodes.

Open Access

Abstract

The disorder known as Jonathan spot commonly observed on ‘Jonathan’ apples actually consists of 2 spot types which must be distinguished in order to define the affecting factors and to resolve the confusing and contradictory evidence in the literature. The spots which occur in the epidermal tissues without definite relation to lenticels are considered as Jonathan spot. Those which occur directly around the lenticels are defined as lenticel spots.

Histologically, the epidermal tissues afflicted with Jonathan spot showed a significant radial compression of the collenchyma cells in the 4 to 7 subepidermal tiers; whereas, such modification was not always apparent in tissues affected with lenticel spot. For the latter, some degree of rupture of the epidermis and the 3 to 5 subepidermal collenchyma tiers was usually noted. Jonathan spot development was inhibited by high temperature (70°F). It was favored by delayed harvest, yet none was observed until the fruit was stored at low temperature for several months. Conversely, lenticel spot often was present at harvest time and its development was accelerated at high temperature and inhibited at low temperature. High relative humidity (90%) enhanced lenticel spot development, whereas, humidity level had no effect on Jonathan spot.

Open Access