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Nodal sections of the winter-hardy 'John Franklin' rose cultivar from field-grown plants were cultured on a modified Murashige and Skoog (MS) nutrient medium. Very high levels of contamination from the surface of the initial sections required that plants be grown under greenhouse conditions. Rose plantlets obtained from subsequent subcultures were used for the first time in a radiotracer experiment with $ sp{32}$P to study the kinetics of phosphorus (P) uptake as a function of temperature of the nutrient medium. P uptake increased with time for rooted and non-rooted plantlets in a linear fashion that did not reach an equilibrium value even after 96 hours of exposure. An analysis of variance revealed that the plantlets with roots absorbed significantly greater amounts of P at the 0.01 level compared with non-rooted plantlets at 22$ sp circ$C. P uptake was significantly higher at the 0.05 level, for rooted versus non-rooted plantlets at 33$ sp circ$C. There was no significant difference in P uptake by rooted and non-rooted plantlets at 3$ sp circ$C. Interaction between time of exposures and rooting was found to be significant at 22$ sp circ$C and 33$ sp circ$C at the 0.01 level. The results indicated that the root system, previously thought to be inefficient in the nutrient absorption, played a key role in absorbing P from the nutrient medium at optimum temperature.

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Phenotypic characterizations demonstrated that diversity among 19 naturalized North American and 5 commercial Kura clover ( Trifolium ambiguum M.B.) rhizobial strains was limited. Growth chamber and field evaluations indicated the superiority of North American isolates, increasing foliage accumulation by 30% when compared to commercial inoculant strains. Nitrogen fertilization, however, produced greater accumulations in all evaluations. Genetic diversity among 128 isolates from the lower Caucasus was significant. Nodulation specificity of rhizobia from the lower Caucasus was demonstrated to be more complex than what was reported in the literature, as plants of different ploidy levels and even of different species were, in some cases, nodulated by the same isolate. Specificity of a given rhizobial strain varied depending on the isolate. This study identified naturalized North American rhizobial isolates that are more efficient than currently used commercial strains and increased the genetic diversity of Kura clover rhizobia currently available.

Lowland rice production is expanding throughout South-East Asia necessarily onto soils of poorer nutrient status with a resulting decrease in yields. An understanding of the nutrient status of the rice rhizosphere is essential for the development of appropriate management practices to increase rice yields. Phosphorus (P) deficiency is one aspect of rice nutrition. Increased rice root respiration and P uptake efficiency, and an increase in H$ sp{+}$ released from roots and enhanced solubility of calcium phosphates are two possible mechanisms of tolerance to low P levels. These mechanisms were evaluated but could not be used as single tests to differentiate among cultivars for tolerance to P deficiency. Phosphorus reactions in the soil may be confounded by the chemistry of iron (Fe). Iron and P interactions in the rice rhizosphere were investigated using a Philippine paddy soil. Root loss of oxygen (O$ sb2$) into the rhizosphere caused the oxidation of Fe$ sp{2+}$ and the concurrent release of H$ sp{+}$. Root release of H$ sp{+}$ from cation-anion uptake imbalances also contributed to the acidification of the rhizosphere. Accumulation of Fe$ sp{3+}$ was found next to the root plane. Depletion of acid-soluble P coincided with the zone of acidification. Rice plants were able to utilize the acid-soluble P fraction during growth.

The initiation and development of adventitious roots in cuttings are highly complex processes, influenced by both endogenous and exogenous factors. These vary from the environmental factors prior to the striking of the cutting, to the anatomical and physiological factors, within the stem. Encompassed are the nutrient status, physiological age and degree of differentiation of the tissues, and the balance of endogenous rooting inhibitors and/or promoters (including hormones). The role of cytokinins in root initiation and development has been perceived as that of an inhibitor. This investigation considered several aspects of the role played by cytokinins in the process of root development. A qualitative/quantitative analysis of the cytokinin-like activity in stem cuttings of several plants, including both easy- and difficult-to-root species was conducted on a comparative basis. There was no clear correlation between the type / level of cytokinins detected in the cuttings and the relative ease of root formation. Both qualitative and quantitative changes in the compounds exhibiting activity in the soybean callus bioassay were observed over the period of root formation in Impatiens stem cuttings. The effects on root formation in cuttings of exogenously applied auxins and cytokinins were investigated. Auxins generally promoted root number and elongation at relatively high concentrations (10[-4] M), but showed less effect on lateral root initiation and development. At high concentrations, cytokinins strongly inhibited root development, but did promote lateral root growth. In suspension culture, the effect of these hormones differed slightly, with IAA and IBA having no significant effect on root development, but NAA strongly stimulating lateral root initiation. Zeatin (10¯¹¹ M) significantly increased root length and the number of lateral roots produced. The effect of treatment of the stem cuttings with potassium permanganate and centrifugation was examined. While both these treatments have been perceived to increase root production in cuttings, no significant improvement in rooting ability following centrifugation (relative to the control) was observed. Impatiens cuttings centrifuged in the presence of distilled water showed a significantly reduced rooting ability relative to those centrifuged in the dry state. Treatment with an 8-hour pulse in 0.05 % potassium permanganate significantly increased the average root length. These treatments had an effect on the cytokinin levels and distribution in the stem cuttings. Slightly higher levels of cytokinins were associated with the increase in root number and length in both experiments. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

To test the hypothesis that red-osier dogwood cuttings from a more stressful edaphic environment (dry site) would have a greater salinity tolerance compared with cuttings from a less stressful environment (moist site) a greenhouse experiment was designed. Cuttings collected from three sites in southeastern Manitoba varying in edaphic conditions (moisture) were exposed to 0, 25, 50, or 100 mM NaCl in hydroponics. After four weeks of treatment, physiological parameters were measured. No differences in salinity tolerance were observed between the sites; nevertheless, this study supported previous results suggesting that red-osier dogwood can limit the transport of Na+ from the root to the shoot. To determine the presence of barriers to ion movement, the roots of red-osier dogwood exposed to NaCl were sectioned and observed using brightfield and fluorescence techniques. A modified outer cortical layer was observed suggesting the presence of an exodermis, which would be an additional barrier to Na+ and Cl- movement. Furthermore, the maturation of the endodermis and exodermis occurring closer to the root tip could also contribute to limiting the transport of Na+ to the shoot.

Soybean [Glycine max (L.) Merr.] is a tropical to subtropical legume that requires root zone temperatures (RZTs) in the 25 to 30°C range for optimal symbiotic activity. The inability of soybean to adapt to cool soil conditions limits its development and yield in short season areas. In particular, nodulation and nitrogen fixation by this crop species is sensitive to cool RZTs. The isoflavone genistein, which is the most effective plant-to-bacterium signal in the soybean nitrogen fixation symbiosis, has been used to pretreat Bradyrhizobium japonicum inocula. This resulted in increased soybean nodulation and nitrogen fixation in several studies, indicating that genistein preincubated inocula could overcome low RZT inhibition of plant growth and yield. The effectiveness of isoflavones was found to vary among soybean cultivars. Some legume cultivars apparently supply limiting amounts of the flavonoids. The objective of this thesis was to determine how soybean cultivars of different maturity groups would respond to genistein incubation of B. japonicum prior to inoculation. Two field experiments were conducted in 1997 and 1998 involving eleven soybean cultivars of three maturity groups organized in a randomized complete block design. Cells of B. japonicum, treated with genistein or not, were applied onto seeds in the furrow at the time of planting. The results of this study indicated that genistein application increased nodule number and nodule dry matter per plant, increased plant nitrogen content, grain protein and grain yield of all cultivars. There was no interaction between maturity group and genistein application, and there was no correlation between maturity groups and increase in nodulation, total biomass, nitrogen content and yield due to genistein treatment. Thus, responses of soybean cultivars of different maturity groups to genistein treatment are not related to maturity and/or yield potential.

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