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Yong Cheong Koh and Fred T. Davies Jr.

The leaves of vegetative stolons of greenhouse grown Cryptanthus `Marian Oppenheimer' (wide leaf clone) were cultured in modified MS media to induce adventitious shoot formation via callus formation. The best callus induction medium was basal MS medium with 10 μM NAA, IBA and BA. Pure green (843), maroon (3), striped (2) and albino plantlets were obtained. Most of the albino plantlets were stunted, tightly clumped together and impossible to score. The medium which produced the highest average number of non-albino plantlets was basal MS medium with 0.3 μM NAA, IBA and BA All non-albino plantlets were rooted in MS medium with 5.4 μM NAA and transplanted ex vitro with a survival rate of 96.7%. The maroon plantlets became green two weeks after transplanting. Histological studies revealed that C. `Marian Oppenheimer' (wide leaf clone) has two tunicas (L1 and L2) and a corpus (L3). Callus on the leaf explant arose mainly from the L2 and L3. Apparently C. `Marian Oppenheimer' (wide leaf clone) is a GWG periclinal chimera.

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Michael Marcotrigiano and Susan P. McGlew

In an effort to accelerate breeding programs and to study somaclonal variation, a micropropagation system was devised for cranberries (Vaccinium macrocarpon). Using a factorial design, explants taken from greenhouse grown plants were placed on Anderson's medium containing different concentrations of 2ip' GA3, and IBA, with 4 cultivars tested over 3 subcultures. In other experiments, explant source, macro and micro salt formulations, and rooting treatments, were studied. Optimal multiplication and shoot quality occurred when single node explants taken from greenhouse grown plants were placed on Anderson's media containing 150 uM 2iP, 1.0 uM IBA and no GA3. Histological examinations indicate that initial response is axillary bud proliferation but upon subculture adventitious shoot formation may be possible. Proliferated shoots could be rooted ex vitro in plug trays under plastic tents and without hormone treatments. Optimal rooting occurred under high light conditions in a 1:1 (v:v) peat:sand mix. Plants were easily transplanted into the field in spring and will be evaluated by comparison to conventionally propagated material.

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Takuya Tetsumura and Hisajiro Yukinaga

When cultured in vitro, roots of four Japanese persimmon (Diospyros kaki L.) cultivars formed adventitious shoots on MS medium with 10 μm zeatin and 0.01 μm indole-3-acetic acid, although their organogenetic capacities varied. Histological study revealed that the origin of the adventitious shoots was the pericycle. The regenerated shoots grew well on the shoot proliferation medium (MS with 5 μm zeatin). Final rooting percentages of shoots regenerated from roots of three of the four cultivars were greater than those of shoots that originated from shoot tips and that had been subcultured >50 times. Shoots regenerated from `Jiro' roots rooted 10 days earlier, had more roots than those from shoot tips, and maintained higher rooting ability over ten subcultures. Rooted `Hiratanenashi' shoots regenerated from roots survived better after acclimatization than those from shoot tips. No obvious variants were observed either in vitro or in the field. The trees regenerated from roots flowered within 4 years. These findings suggest that partial rather than true rejuvenation was responsible for both the early flowering and the juvenile characteristics, i.e., the enhanced rooting ability, observed in the regenerated plants. Chemical name used: 6-(4-hydroxy-3-methylbut-2-enylamino) purine (zeatin).

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Tekalign Tsegaw, S. Hammes, and J. Robbertse

Potato (Solanum tuberosum L.) treatment with paclobutrazol resulted in short and compact plants having dark green and thicker leaves, and wider stem and root diameters. Investigating the underlying anatomical modifications in response to the treatment was the objective of the study. Plants of potato cultivar BP 1 were treated with 0, 45.0, 67.5, and 90.0 mg paclobutrazol per plant as a foliar spray. A month after treatment leaf, stem and root materials were taken from the control and plants treated with 67.5 mg paclobutrazol, and histological observations were made using light microscope. Leaves of treated plants showed an increased chlorophyll a and b contents, thicker epicuticular wax layer, elongated and thicker epidermal, palisade and spongy mesophyll cells. paclobutrazol increased stem diameter by about 58% due to induction of thicker cortex, larger vascular bundles, and wider pith diameter associated with larger pith cells. Widening the cortex and the induction of more secondary xylem vessels in response to paclobutrazol treatment increased the root diameter by about 52%. Paclobutrazol treatment remarkably increased the accumulation of starch granules in the stem pith cells and cortical cells of the stem and root. This study is similar to the other relevant studies in reporting an increased leaf thickness, and stem and root diameters; however, most of the underlying anatomical modifications described above have not been reported previously.

Open access

G. E. Evans and H. P. Rasmussen

Abstract

Comparative studies of clonal anatomy revealed visible differences in medullary ray cell diam in juniper cultivars with different chromosome numbers. Histological studies, made at 10-day intervals for 60 days after grafting showed no differences in developmental sequence but only differences in rate at which each stage occurred. Callus tissue form ation began 10 - 20 days after grafting; first in ‘Fountain’ and last in ‘Pfitzeriana Kallay’. Isodiametric cells from uninjured cambia appeared by the 20th day except with ‘Pfitzeriana Kallay’ scions. By an alternating series of radial and tangential divisions, these cells overwalled the injured graft surfaces, but was less pronounced in closely fitted grafts. Overwalling cells did not occur in ‘Pfitzeriana Kallay’ until 30 days after grafting. By 40 - 50 days, overwalling cells began, by radial divisions to produce organized cells which filled voids between graft partners and crushed intervening callus. Mixing of newly formed cells between stock and scion cambia occurred 50 - 60 days after grafting. These cells assumed the spindle-shape of typical tracheids and were oriented into a “cambial bridge.” New, normally oriented xylem subsequently formed from this new cambial tissue. In typical grafts, most new tissue arose from the understock prior to the 50th day after grafting. At 60 days, contribution from stock and scion were equivalent. Adjacent walls of mixed graft tissue were found to be unmodified and appeared as paired structures each with a middle lamella and secondary wall thickenings. Abnormally large numbers of pits were observed at the graft union.

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Kay P. Gersch, Carl E. Motsenbocker, and Gregory A. Lang

-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

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J.T.A. Proctor, T. Slimmon, and P.K. Saxena

Ginseng is an herbaceous perennial that grows in the understorey of deciduous hardwood forests and is also cultivated for its highly valued root. The primary method of propagation of ginseng is by seed which requires the breaking of dormancy by stratification, a process which takes 18–24 months. Investigation of factors controlling the growth and development of ginseng plants is a prerequisite to the development of a more efficient system of ginseng propagation. We have recently modulated the morphogenetic potential of geranium roots and stimulated de novo development of shoots and embryo-like structures which later formed whole plants using thidiazuron (TDZ). Our objective was to investigate the morphological changes in seedling and mature ginseng plants induced by TDZ, particularly in relation to root and shoot morphogenesis and economic yield. Applications of TDZ (0.22 and 2.20 ppm), either as foliar sprays or soil watering to greenhouse-grown seedlings over 18 weeks (2 weeks after sowing to 20 weeks when plants were harvested) induced similar effects. These responses included increased stem length and diameter, and shoot and root weight (economic yield). Single foliar applications of TDZ at 62.5 and 125 ppm to 3-year-old field-grown ginseng plants 3 months before harvest increased root biomass (economic yield) by 19% to 23%. Roots of TDZ-treated seedlings and 3-year-old field-grown plants developed thickened secondary roots on the upper part of the taproot. The root-like structure of these secondary roots was confirmed by histology. In addition, TDZ treatments induced adventitious buds on the shoulder of 3-year-old roots. These buds developed into shoots to give multi-stem plants following a period of dormancy, which was overcome with GA3 (gibberellic acid) treatment before planting.

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Mary Jean Welser and Martin C. Goffinet

Grapevine yellows is a destructive, worldwide disease of grapevines that is caused by a phytoplasma, a bacterium-like organism that infects and disrupts the vascular system of shoots. The North American form of grapevine yellows (NAGY) has been observed in New York State since the mid-1970s and in Virginia since the mid-1990s. Symptoms duplicate those of vines suffering from an Australian disease complex known as Australian grapevine yellows (AGY). We sought to determine if infected `Chardonnay' vines have common anatomical characteristics across the three regions. At each geographic site in late summer, 2003–04, leaf and internode samples were taken from younger green regions of shoots and from mature basal regions in the fruiting zone. These were processed for histology. The anatomy of each organ type was compared between locations on the shoot, between geographic locations, and between affected and normal shoots. The phloem was the only tissue universally affected in vines with NAGY or AGY symptoms. In stem internodes, both primary phloem and secondary phloem showed many senescent cells, abnormally proliferated giant cells, and hyperplasia. In affected secondary phloem there was disruption of the radial files of cells that normally differentiate from the cambium into mature phloem cell types. Normal bands of secondary phloem fibers (“hard phloem”) in internodes were weak or absent in affected vines. Leaves also had disrupted phloem organization but near-normal xylem organization in vines with symptoms. Leaves of infected vines frequently showed a disruption of sugar transport out of the leaf blades, manifested by a heavy buildup of starch in chloroplasts of mesophyll cells and bundle-sheath cells.

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Alessandro Abruzzese, Ilaria Mignani, and Sergio M. Cocucci

Apple (Malus domestica Borkh.) trees are often affected by a severe June fruit drop, which is often correlated with competition phenomena involving fruit nutrition. This research was initiated to determine if June drop in `Gloster'/M.9 apple could be correlated with a diminished nutrient availability in developing seeds and fruit. During the test period [30 to 62 days after full bloom (AFB)], the fruit that abscised had a diameter similar to that reached by persisting fruit 13 days earlier. Biochemical parameters related to nutritional status of fruit were measured when an abscission peak occurred 38 days AFB. Persisting fruit (control) and abscised fruit were compared along with fruit that abscise 13 days later. The cortex tissue obtained from the two kinds of abscised fruit showed a higher level of soluble reducing sugars and sucrose and a lower content of K+, acid hydrolyzable polysaccharides, and protein compared to the control. Further, the Ca2+ content was higher in abscised fruit than in controls of the same age, whereas there was no difference when fruit of the same size were compared. Total amino acid level was similar in control and abscised fruit at the same age, but there was a lower amino acid level in abscised fruit of the same size. Histological analysis of cortex tissue indicated that abscised fruit have larger cells with less evident nuclei and thinner cell walls than controls. Compared to control fruit, abscised fruit showed the same average number of seeds and a severe inhibition of seed growth; seeds from both kinds of abscised fruit had the same or higher levels of the parameters measured. No positive correlations were observed between fruit abscission and nutrient content of seeds or fruit.

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Benoît Bertrand, Hervé Etienne, and Albertus Eskes

In order to avoid nematode damage to roots of Coffea arabica L. in Latin America, a common practice is interspecific grafting on C. canephora var. Robusta (Pierre) rootstocks. The performance of two C. arabica cultivars, `Caturra' and `Catimor T5175', was evaluated on four rootstocks: C. canephora var. Robusta (`T3561' and `T3757') and C. liberica var. liberica (Hiern) and var. dewevrei (Lebrun), over 5 years in a trial at 1180 m elevation in Costa Rica. Nongrafted plants of the two Arabica cultivars were used as controls. Mortality of plants grafted on the two C. liberica cvs. was >20% vs. 6% to 13% for plants grafted on C. canephora, and 3% to 4% for the two controls. Analysis of accumulated yields over four harvests showed that the rootstocks limited stem girth and reduced yield 10% to 48%. Yield on the C. canephora rootstock was greater than that on the two C. liberica cultivars. However, grafting did not affect female fertility (peaberries, empty berries) or content of several chemicals, such as caffeine, fat, and sucrose. The two C. liberica rootstocks significantly reduced aroma and bean size. Histological studies revealed symptoms of incompatibility, characterized by more dilated and less distinct growth rings and appearance of plugged vascular connections. The poor performance of the rootstocks may therefore be explained by partial incompatibility. However, growth and productivity were also affected by poor adaptations of C. canephora, C. liberica, and C. dewevrei to the lower temperature at high altitudes and by morphological differences in the root systems. These results emphasize the need to develop better adapted rootstock cultivars from C. canephora var. Robusta.