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Call number: LD2668 .T4 1951 T83 / Master of Science

In a series of greenhouse experiments, isolates representing serotypically distinct subpopulations of Rhizobium leguminosarum bv. trifolii recovered from root nodules of field-grown subclover Trifolium subterraneum cv. "Nangeela"), were evaluated for their symbiotic effectiveness potential, their effect on regrowth potential of subclover, and for their competitive abilities to form nodules. Isolates from the nodule dominant serotypes AS6, AS6-21, and AS21 were shown to be suboptimally effective at fixing nitrogen gas (N₂) relative to RT162X95, a highly effective commercial inoculant strain. Although the majority of isolates representing the minor nodule occupying serotypes AS27, AG4, and AP17 were also shown to be of moderate effectiveness, isolates ADS14 and RW11 of serotype AS27 were equally as effective as RT162X95. Subclover regrowth was influenced by the severity of the first harvest. Plant-isolate combinations possessing superior N₂-fixing capabilities were more adversely affected by severe clipping than were the less effective combinations. Isolate 88FL3,5, a mediocre N₂-fixing member of the nodule dominant serotype AS6, was not universally more competitive at forming nodules than other isolates. Although 88FL3,5 formed more nodules than many of the other isolates when mixed in equal numbers with each of them separately, isolates ADS14 and ADS16 significantly outcompeted 88FL3,5 even though they represented a minor nodule occupying serotype, AS27. The nodule occupying successes of 88FL3,5 or ADS16 could be overcome if their respective competitor had a numerical advantage ranging between 10:1 and 25:1. Since the soil-borne population of 88FL3,5 has been shown to outnumber other subpopulations of rhizobia in the same soil by at least 10:1, it is not surprising that it can occupy the majority of nodules on field-grown plants even in the presence of more competitive types. Why the highly effective and highly competitive members of serotype AS27 are rarely recovered from nodules of field-grown Trifolium subterraneum L. is a question that merits further study. / Graduation date: 1992

A total of 43 Rhizobium leguminosarium bv. trifolii isolates were obtained from soil samples of two ball clover (Trifolium nigrescens) pastures from Iola and Kilgore (Texas) using ball clover as capture plants. The isolates were phenotypically characterized by intrinsic antibiotic resistance (IAR) against a range of concentrations of eight antibiotics, and by the utilization of 95 different carbon sources (BIOLOG system). The rhizobial isolates were also evaluated for their tolerance to salinity, high temperatures and low pH. The isolates showed two different ranges of growth rates: fast-growing (doubling times between 1.4 - 3.7 h) and slow- growing isolates (12.3 - 21.3 h). The numerical analysis of the phenotypic characteristics showed that the 43 isolates could be grouped in 24 different strains. Cluster analysis based on sensitivity responses of IAR, metabolic profiles of BIOLOG and salt, temperature and acidity tolerance levels could distinguish the Rhizobium strains from a Pseudomonas isolate. The analysis also showed that the rhizobial strains isolated from ball clover nodules are different from a commercial R. leguminosarium bv. trifolii strain used as inoculant for this legume.

Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Jan. 14, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Plant Science, [Department of] Agriculture, Food and Nutritional Sciences, University of Alberta. Includes bibliographical references.

Thesis (Ph. D.) -- Lincoln University, 2009. / Also available via the World Wide Web.

Thesis (Ph. D.)--University of Michigan, 1922. / "Reprinted from American journal of botany, vol. XI, no. 3, March, 1924." Bibliography: p. 156-158.

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