. and Clematis maritima L., primary phloem fiber and collenchyma are displaced outward by plant development, which led to disrupting the mechanical integrity, but not in semiself-supporting Clematis recta L. ( Rowe et al., 2004 ). Modulus of
seedlings ranged from 6% to 93%. For intraspecific grafts of Chinese chestnut, few unions were formed and 6% to 10% of the trees survived after 6 months when side veneer graft cuts were made through phloem fibers in rootstock stems. Because grafting success
emergence. Roots arising from the cambium and phloem regions in Vaccinium corymbosum L. hardwood cuttings were reportedly impeded by a continuous layer of lignified pericyclic fibers and by the epidermis ( Mahlstede and Watson, 1952 ). In some instances, a
limitations given the tightly knitted cellulose/hemicellulose fiber structure ( Cosgrove and Jarvis, 2012 ). Studies using a variety of techniques have estimated the pore size of cell walls to be generally ≤10 nm ( Albersheim et al., 2010 ; Carpita et al
The effects of growth-retarding chemicals on stem anatomy were compared on poinsettia (Euphorbia pulcherrima Wind. `Annette Hegg Dark Red'). Micrographic examinations revealed that secondary walls of nonsclerotic phloem fiber cells were either completely or greatly reduced by retardant treatment. Wall thickening of phloem fiber cells was eliminated by paclobutrazol foliar sprays at 25 mg·liter-1. Fiber cell development was reduced, but not eliminated, by sprays of chlormequat and ancymidol at standard rates, while the triazole uniconazole at 10 mg·liter-1 permitted only limited fiber wall thickening. Chemical names used: (2-chloroethyl)-trimethyl ammonium chloride (chlormequat); α -cyclopropylα- (4-methoxyphenyl) -5-pyrimidine methanol (ancymidol); (E)-(p -chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl-1-penten-3-ol (uniconazole): and (R*,R*)- β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)- 1 H-1,2,4,triazole-1-ethanol (paclobutrazol).
Abstract
Succinic acid 2,2-dimethyl hydrazide (Alar) 2 was applied as 3 weekly foliar sprays at concentrations of 0, 1000, and 2000 ppm to ‘Sovereign’, an Fj cultivar of Tagetes erecta L., grown in a complete nutrient supply under long and short day photoperiods. Plants were sampled for anatomical study one week later. Treated plants grown under long days had thicker leaves and a larger root diameter. In short days, the capitula of treated plants were one-half the size of the untreated ones. The amount of phloem fibers in treated plants was less and cortical and pith cells were shorter in both photoperiods. Alar affected cell wall formation and the phloem fibers in the stems were thinner walled and less sclerified.
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.
Uniconazole was applied as a foliar spray at 0, 90, 130, 170, or 210 ppm to rooted stem cuttings of `Spectabilis' forsythia (Forsythia xintermedia Zab.) potted in calcined clay. Uniconazole resulted in higher total leaf chlorophyll (chlorophyll + chlorophyll,) concentration and a decreased ratio of chlorophyll a: b. Stomata1 density of the most recently matured leaves increased linearly with increasing uniconazole concentration 40, 60, and 100 days after treatment (DAT). The number of stomata per leaf (stomata1 index) increased linearly with increasing concentration of uniconazole throughout the initial 100 DAT. Uniconazole suppressed stomata1 length at all sampling dates and the level of suppression increased with increasing concentration of uniconazole from 20 to 100 DAT. Stomata1 width was suppressed by uniconazole at 40 DAT. Leaves developed after uniconazole application had higher levels of net photosynthesis when measured 55, 77, and 365 DAT. Stomata1 conductance for uniconazole-treated plants was higher compared to nontreated control (0 mg·liter-1) plants when measured 49, 55, 77, and 365 DAT. Initiation of secondary xylem for stem tissues of uniconazole-treated plants was suppressed and expansion of xylem vessel length and width was less. Secondary phloem tissues of stems from uniconazole-treated plants contained larger numbers of phloem fibers having smaller cross sectional areas than phloem fibers of controls. Chemical name used: (E)-1-(p-Chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-01 (uniconazole).
Kenaf (Hibiscus cannabinus L.), native to east Africa, is an annual herbaceous member of Malvaceae cultivated primarily for its bast fibers. One of many potential uses of kenaf is that of a growth medium component. Kenaf stems (xylem plus phloem) were ground and sieved to 2 to 5 mm diameter particles. The particles were combined at various volumetric percentages with other components (perlite, vermiculite, calcined clay) in 70% Sphagnum pest moss which received standard preplant fertilization. To avoid growth suppression, the kenaf must be enriched with nitrogen (soaked in NH4NO3 solution for 5 days). Impatiens and tomato bedding plant shoot growth was proportional to both the N concentration of the soak solution and the percentage of N-soaked kenaf in the medium. The N soak solution should be £ 2000 mg N/liter with 30% kenaf or £ 4000 mg N/liter with 10% kenaf. Physical properties (bulk density, total porosity, air porosity and container capacity) of kenaf media were similar to those of a commercial peat-lite. The optimal medium for bedding plant production was 70% pest + 15% calcined clay + 15% kenaf soaked in 2000 mg N/liter. The N-soaked kenaf served successfully both as a medium bulking component and as a slow-release N supply.
Graft compatibility was investigated for 15 Chinese chestnut (Castanea mollissima Bl.) cultivars, nine American chestnut [C. dentata (Marsh.) Borkh.] selections, six Japanese chestnut (C. crenata Sieb.) cultivars, and two putative Japanese hybrids on two known rootstocks of Chinese chestnut. Intraspecific grafting of Chinese chestnut resulted in 80% success after two growing seasons. An unusual anatomical structure of the chestnut stem had a significant effect on graft success. The phloem fiber bundles related to graft failure are described in the study. Interspecific grafts of seven American and five Japanese chestnut selections resulted in ≥70% success. The putative Japanese hybrids had a significantly lower success rate (<50%) regardless of rootstocks. A marked graft incompatibility was found in one Japanese/Chinese and two American/Chinese combinations. Graft incompatibility related to morphological abnormalities at the graft union was also observed in interspecific grafts. Comparisons of cambial isoperoxidase isozymes between successful and unsuccessful grafts did not support the hypothesis that peroxidase isozymes are indicators of rootstock-scion compatibility. The results suggest that genetic incompatibility is not a major cause of graft failure in Chinese chestnut.