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Abstract

Various histological criteria were employed in studying the chronological and morphological development of the apex of field-grown plants of Brassica oleracea var. italica, cv. ‘Coastal’. Time of differentiation was based on changes in the size and configuration of the apex. The earliest evidence of reproductive differentiation was 5 weeks after sowing or at the time of macroscopic appearance and unfolding of the eighth true leaf. First order floral stalks began to appear at 7 weeks or at the time of macroscopic appearance of the 14th true leaf. Thus, the time interval for the transition from a vegetative to a reproductive apex appears to be approximately 2 weeks, under field conditions. By 9 weeks after sowing, or after the macroscopic appearance of the 22nd true leaf, second order floral stalk initiation and hence inflorescent head formation predominated.

Abstract

Callus tissue of ‘Seyval’ (Seyve-Villard 5-276) (Vitis sp.), a French hybrid grape, formed adventitious embryos when transferred from a medium with 2,4-dichlorophenoxyacetic acid (2,4-D) to a medium containing 1-napthaleneacetic acid (NAA). Embryos began to turn green and develop into apparently normal vines when placed on a medium free of hormones and vitamins in the light. Histological evidence indicated that plants derived from callus originated from embryo-like structures and not from plantlets or excised buds. Secondary embryoids formed on primary embryoids, and tertiary embryoids occasionally formed on secondary embryoids. More than 50 vines and several hundred adventitious embryoids were obtained from approximately one cubic centimeter of callus.

Abstract

Continuous gamma irradiation during polyembryogenesis was tested to determine if the number of embryos could be reduced in ‘Marukinkan’ (Fortunella japonica Swingle), a polyembryonic Citrus relative, and effectively increase the number of F₁ hybrids in crosses. The number of embryos in untreated plants was 10.9, and this number was reduced with increasing exposure rate to 2.4 at 500R/day. The percentage of monoembryonic seeds in untreated plants was 1.1, and this was raised with increasing exposure rate to 34.0% at 500R/day. Cytological and histological observations of polyembryogenesis showed that early adventive embryonic cell divisions were retarded severely by gamma-rays (500R/day), and most of them could not develop beyond the stage of small globular proembryos consisting of 1 to 4 cells. These proembryos finally disappeared, but the fertilized embryo generally survived, probably because of a division earlier than those of adventive embryos and a vigor afforded to fertilized cells.

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).

Abstract

Bush type snap beans (Phaseolus vulgaris L.) with resistance to the root-knot nematode, Meloidogyne incognita (cotton strain) are being developed by using PI-165426 as the resistant parent. PI-165426 (resistant), ‘Black Valentine’ (susceptible) and F₅ breeding line B3864 (resistant) were inoculated with second-stage larvae. There were no significant differences in larval penetration of roots. Root tips showed slight swellings at infection loci of resistant and susceptible plants. Necrosis was evident in the resistant lines 4 days after inoculation. Histological studies of early infections showed that resistance was due to absence of adequate giant cell development and to hypersensitive reaction within the infected portion of the root. When soil temperature was changed from 16 to 28°C, galling, female development, and egg mass production in the resistant plants were increased.

An interspecific hybridization program involving five species of Impatiens was initiated to delineate incompatibility barriers. With the exception of one cross, no viable hybrid seed was recovered. Fluorescence microscopy revealed foreign pollen tubes to reach ovules in all crosses, although not all ovules were approached. A histological study involving I. auricoma Baill. and I. walleriana Hook f. ensued to confirm the presence of hybrid embryos. Developing I. walleriana × I. auricoma and reciprocal hybrid embryos were compared to self embryos. Development of hybrid embryos was delayed as early as five days post-pollination. I. walleriana × I. auricoma embryos continued to develop for 8 days post-pollination, but did not reach a size greater than a 5-day self embryo. Excessive endosperm was observed in the hybrid. I. auricoma × I. walleriana embryos continued to enlarge up to ovary abortion but did not reach a size greater than a 7-day self embryo and little to no endosperm developed. Disintegration of ovules included disorganization and collapse of the endosperm, and vacuolization and loss of turgidity of the embryo.

Ginseng is a very valuable agricultural species grown for its root, which contains pharmacologically active constituents. One limiting factor for expansion of ginseng production is an efficient method for mass propagation. Currently, seeding is the principal method of propagating ginseng, but the embryo of ginseng seeds at harvest is immature. A stratification schedule consisting of a cool-warm-cool temperature treatment over 18-22 months is required for embryo development and seed germination. An alternative for the efficient production of ginseng is mass propagation through the use of in vitro culture techniques. The objective of this work was to develop a highly efficient system for regeneration of ginseng. The efficacy of three auxins, viz. 2,4-D, NAA and dicamba, were compared for the induction of somatic embryogenesis in American ginseng. Somatic embryos formed on ginseng cotyledonary, zygotic embryo, and shoot explants after 8 weeks of induction by the auxins. Significantly more somatic embryos were induced by culture of any of the ginseng explants on media supplemented with 5 μmol·L^-1 2,4-D than any other auxin treatment. Histological and SEM studies confirmed that the regenerants were somatic embryos. Somatic embryos germinated and developed into normal plants in 3-6 months. The development of a regeneration system for ginseng using somatic embryogenesis is a necessary first step for mass propagation and the improvement of American ginseng.

Northeastern U.S. grape growers have become more knowledgeable about many aspects of grape production, including pruning and training, canopy management, nutritional recommendations, pest and disease management strategies, vineyard floor management, etc. Important to all these aspects is a firm understanding of vine structure and development. Yet, there is no current publication on vine growth and development that growers and researchers can consult to gain an understanding of the organs, tissues, and developmental processes that contribute to growth and production of quality vines in the northeastern U.S. climate. A concerted effort is underway to secure enough information on how vines are constructed, grow, and develop in the northeast so that a publication useful to a wide audience can be produced. Our objective is to consolidate information already on hand that can help explain the internal and external structures of grapevines that are pertinent to the needs of northeast growers, to add information that is lacking by collecting and examining vine parts, and to work toward integrating vine structure with vine physiology and viticultural practices. Over the past decade, organs of various native American, French hybrid, and vinifera varieties have been collected from vineyards at Cornell's experiment stations and from growers' vineyards in the Finger Lakes and Lake Erie regions. Much quantitative data on vine development have been collected and interpreted. Lab work has included dissections of organs, histological and microscopic examination, microphotography, and the production of interpretive diagrams and charts. A list of the subject matter and examples of visual materials will be presented.

Histological and histochemical examination of floral initiation was conducted to determine the pattern of flowering in Rudbeckia hirta, a long-day (LD) plant. Plants were grown under 8-hour short days (SDs) until they had 14 to 16 expanded leaves. Half of the group of plants was moved to LD conditions consisting of natural daylength plus a 4-hour night interruption. Rudbeckia hirta had a pattern of differentiation in flowering similar to that reported in species requiring one inductive day for initiation. Rudbeckia hirta required 8 LDs for evocation and 18 LDs for completion of initiation. Involucral bracts initiated after 18 LDs, after which the receptacle enlarged and was capped by a meristematic mantle of cells signaling the start of development. Floret primordia did not initiate, even after 20 LDs. Increases in pyronin staining were observed in actively dividing cells of the procambium, leaf primordium, and corpus of the vegetative meristems. After 8 LDs, the pith rib meristem stained darkly, a result indicating the arrival of the floral stimulus. An increase in pyronin staining was also observed in the meristematic mantle covering the receptacle after 18 LDs, a result indicating increased RNA levels.

Zygotic and somatic embryos are purported to follow similar developmental sequences, but few investigations have thoroughly compared the two processes. Developing pods of Cercis canadensis L. (redbud) were collected from trees on the Knoxville campus of the University of Tennessee once or twice per week from 28 March to 8 August 1991. At least 10 ovules/sample date were fixed in FAA to evaluate zygotic embryo ontogeny. A minimum of 40 ovules/sample date were aseptically excised and placed on SH medium supplemented with 9.0 μM 2,4-D and 5 mM ammonium ion to initate somatic embryogenesis. Zygotic and somatic embryos were prepared for histological examination using standard paraffin techniques. Somatic embryos developed primarily from cotyledons and epicotyls of zygotic embryos mat were cultured between 6 June and 19 July. Somatic and zygotic embryos were subtended by multiseriate suspensors and progressed through recognizable globular, cordate and cotyledonary stages of development. Cotyledon morphology was similar for both embryo types. However, many somatic embryos failed to differentiate dome-shaped shoot meristems exhibited by their zygotic counterparts.