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- Author or Editor: N. Mays x
Somatic embryogenesis from leaf midrib explants of Dendranthema grandiflora Tzvelev. `Iridon' cultured on modified Murashige and Skoog basal medium (MSB) containing 1.0 mg 2,4-D and 0.2 mg BA/liter was influenced by light and sucrose concentration. Somatic embryos formed directly from explants when cultured on medium containing 9% to 18% sucrose and incubated first in the dark for 28 days, followed by 10 days in light, and then returned to the dark for 14 days. Embryogenesis did not occur in continuous darkness and was drastically reduced when explants were incubated in light only. The most embryos were formed on medium containing either 12% or 15% sucrose; lower concentrations stimulated shoot and root development. Light also mediated embryogenesis from leaf explants of 'other cultivars. White-opaque or occasionally light-green cotyledon-stage somatic embryos germinated on MSB medium without growth regulators but containing 3% sucrose. Twelve of the 23 cultivars evaluated produced somatic embryos, but plants were recovered from only five. Regenerated plants were phenotypically similar to parent plants in growth habit, leaf morphology, and flower color. Chemical names used: N- (phenylmethyl)-1 H- purine-6-amine (BA); (2,4-dichlorophenoxy) acetic acid (2,4-D).
A tissue culture laboratory exercise illustrating regeneration of whole plants from leaf segments of chrysanthemum by organogenesis is described. Using simple, common media, shoots can be generated in 5 weeks and rooted after an additional 3 weeks. Acclimatization of plants can be accomplished in a simple mistbed in the greenhouse. The exercise is adaptable to depict genotype differences among cultivars, optimization of shoot induction, effects of growth regulators, and experimental design. Callus is typically not formed during shoot formation; however, co-cultivation of leaf segments with a virulent strain of Agrobacterium tumefaciens produces callus with a strain of disarmed A. tumefaciens harboring NPTII construct affects regeneration of plants resistant to kanamycin.
Stolons of `Raleigh', `Floratam', and FX-332 St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] were sampled from the field between October and March in two consecutive years to evaluate accuracy of an electrolyte leakage (EL) method for predicting freezing tolerance. Lethal temperatures of stolons estimated using EL were compared to those obtained by regrowth tests in the greenhouse. Mean lethal low temperatures for regrowth and EL methods over 12 sampling dates were `Floratam', –4.5C (regrowth) vs. –4.4C (EL); FX-332, –4.2C (regrowth) vs. –4.9C (EL); and `Raleigh', –6.0C (regrowth) vs. –5.4C (EL). A positive correlation (r = 0.81) was observed between EL-predicted and regrowth lethal temperatures for `Raleigh', which exhibited some acclimation during the first sampling year. The EL technique consistently predicted a lower lethal temperature for `Raleigh' than for `Floratam', which corroborates field observations concerning freezing tolerance of these two cultivars.
Little is known about intraspecific variability in St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] freezing tolerance and the physiological factors that may influence survival. Stolons of field-grown `Raleigh', `Floratam', and FX-332 St. Augustinegrass were sampled between October and March in 1990 to 1991 and 1991 to 1992 to measure freezing tolerance, nonstructural carbohydrates, and water content. Stolons were exposed to temperatures between 1 and -8C in a freezer, and regrowth was evaluated in the greenhouse. Generally, freezing tolerance of `Raleigh' > `Floratam' = FX-332. `Raleigh' exhibited >60% survival in December and January, while survival of `Floratam' and FX-332 was <20%. `Raleigh' was the only cultivar that acclimated, as indicated by a 75% increase in survival between October and December 1990. Starch and sucrose were the primary storage carbohydrates extracted from stolons, but neither was correlated with freezing tolerance. A negative (r = -0.80) correlation was observed between `Raleigh' survival and stolon water content between January and March 1991. Reduced water content in `Raleigh' stolons during winter months may contribute to acclimation.
Orchards established on weathered, acidic mineral soils in the Ozark Highlands must be managed to meet tree nutritional requirements. However, a common characteristic of Ozark Highland soils is a relatively low soil organic matter (SOM) concentration, a condition that can have detrimental effects on orchard productivity. Organic orchard management poses specific challenges to managing competitive under-tree vegetation and supplying appropriate supplemental nutrition to maintain tree growth and cropping. In Mar. 2006, an experimental apple orchard was established to evaluate the effects of under tree, in-row groundcover management system (i.e., shredded paper, wood chips, municipal green compost, and mow-blow), and nutrient source (i.e., non-fertilized control, composted poultry litter, and pelletized organic commercial fertilizer) on SOM, carbon (C), and nitrogen (N) concentration, and soil C and N sequestration over time in an organically managed orchard in the Ozark Highlands region of northwest Arkansas. Soil organic matter, total C, and total N concentrations (soil weight basis) and contents (area basis) in the top 7.5 cm increased in all groundcover management systems from 2006 to 2011. The greatest differences were observed with municipal green compost treatments. Significant interactions between groundcover management treatment and nutrient source were only observed for SOM concentration, whereas nutrient source did not affect total C and total N concentrations or contents. Soil C sequestration rates were 0.9, 1.0, and 2.8 Mg·ha−1 per year under the shredded paper, wood chip, and green compost treatments, respectively, whereas total C content did not change over time under the mow-blow treatment. The green compost treatment was the only treatment that had significant total N sequestration occur (0.25 Mg nitrogen/ha/year). Results of this study indicate that organic cultural methods can significantly augment near-surface soil C and N contents, which will likely increase productivity, of apple orchards in the Ozark Highlands over a relatively short period time after establishment. This study has implications for orchards in similar soils or environmental circumstance and for both organic and conventional management systems.