A total of 200 Rhizobium meliloti isolates were sampled from alfalfa (Medicago sativa L.) nodules in five uninoculated fields throughout Arizona. Dominant strains (≥ 20% nodule occupancy at each site) were identified using plasmid profile analysis and intrinsic antibiotic resistance patterns. The major dominant strains and a commercial strain (102F77b) were evaluated for their N fixing effectiveness in a Leonard jar study. All strains were highly effective, and no significant differences were found (p ≥ 0.05) in shoot weight, root weight, nodule weight, acetylene reduction and total N content among the strain treatments. These effective dominant R. meliloti strains indigenous to Arizona soil probably contribute to the state's high alfalfa yield. Furthermore, indigenous strains AZTCYJ, AZSC, and AZY have potential as inoculants for arid lands due to their high effectiveness and unique resistances to extreme abiotic stresses present in arid land soils.

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Forage crops grown in many parts of the Appalachian region are restricted in yields as a consequence of shallow soils, low levels of essential nutrients, toxic levels of aluminum, and low pH. Therefore, the successful growth of alfalfa in these regions is dependent on either changing existing edaphic conditions or modifying the plant physiologically so as to improve nutrient acquisition and utilization. The purpose of the present study was to determine if chemicals reported to possess growth regulatory properties affect nutrient uptake and utilization and how such effects are manifested in the plant. In the first series of experiments, foliar sprays containing 10 mM CaCl₂ with or without tetracosanoic acid (C-24), hexacosanoic acid (C-26), triacontanoic acid (C-30), or dipalmitoyl phosphatidic acid (DPA) were ineffective (p=0.05) in enhancing alfalfa (Medicago sativa, Arc) shoot or root biomass when applied to 21 and 28 day-old plants. DPA treatments also had no effect (p=0.05) on the leakage of Ca²⁺, K⁺, Mg²⁺, and PO₄³⁻ from foliar leaf discs. Foliar treatments containing either 10 mM CaCl₂ + DPA or 10 mM CaC1₂ were effective in increasing shoot biomass in plants grown in solution culture containing suboptimal levels of calcium and phosphate. The increased biomass, however, was attributed to calcium supplementation rather than the effect due to DPA. The second series of experiments evaluated the effect of seed treatments with the growth retardant XE-1019 ((p-chlorophenyl)-4,4-dimethyl-2(1,2.4-triazol-1-yl)-1-penten-3-ol) on alfalfa growth, chlorophyll concentration, ionic leakage, nutrient uptake, and root nodulation. Seed treatments resulted in plants with significantly reduced (p=0.05) shoot and root biomass and thicker greener leaves. Quantitation of leaf chlorophyll indicated that the seed treatments caused significant increases (p=0.05) in both chlorophyll a and b concentrations at initial growth stages. After six weeks, no significant differences in chlorophyll concentrations were detected. XE-1019 had no apparent effect on leaf membrane permeability or transport since no significant differences (p=0.05) were detected in the leakage of Ca²⁺, K⁺, Mg²⁺, and PO₄³⁻ from foliar leaf discs. However, whole plants treated with XE-1019 depleted significantly (p=0.05) higher amounts Ca²⁺, K⁺, Mg²⁺, and PO₄³⁻ from hydroponic solutions on a per centimeter root basis. On a per plant basis, untreated plants absorbed greater quantities of the assayed nutrients. The presence of XE-1019 in the rhizosphere was not deleterious (p=0.05) to the inoculation of the root with Rhizobium meliloti and the subsequent formation of root nodules. Seed treatments with XE-1019 also had no effect on the cultured growth of Rhizobium meliloti strains 102F34a, l02F51a, 102F66d, and 102F77b. / Master of Science