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Results of two studies are reported here, a greenhouse study and a field study. In the greenhouse study, dry matter yield and nitrogen (total and 15N) uptake of leaves, stems and roots of tomato plants (Lycopersicum esculentum Mill., cv. Columbia) subjected to saline stress by NaCl were studied. The integrated effects of responses of these tissues to salinity on the whole plant basis and levels of Na⁺, Cl⁻ and K⁺ accumulation in these tissues were also studied. The treatments consisted of low (control, 0.3 bar), medium (4.3 bars), and high (8.3 bars) salinity. The saline treatments were prepared by adding NaCl to nutrient solution in sand culture. The plants were 80 days old at the start of the treatments and each was in a pot containing 1.8 kg of quartz sand. The ¹⁵N was provided to plants by adding K¹⁵NO₃ to the pots and the 15N treatment continued with the saline treatments up to 30 days. The plants were harvested at each 5-day interval during the treatment period. Dry matter production and nitrogen (total and ¹⁵N) uptake were significantly lower for saline treatments as compared with the control. Differences in dry matter production and ¹⁵N uptake on whole plant basis appeared in the latter part of the treatment period between the two saline treatments. For most of the parameters studied, the leaves were found to be affected most by salinity, the roots were intermediate in their response and the stems were the least affected by salinity. The effect of salinity on the studied parameters were attributed to osmotic effects and specific ion effects of Na⁺ and/or Cl⁻. A field study with two cultivars--Columbia and Pearson was conducted at the Safford Agricultural Center. Three N treatments were used: 0 kg N/ha, 84 kg N/ha and 168 kg N/ha and two treatments consisting of two water sources--river water with an EC of 1.15 dS/m and more saline well water of EC of 2.21 dS/m. Columbia had a significantly higher yield of tomatoes than Pearson for both water types. The N treatments had no effect on tomato yield apparently due to high residual N remaining in the field from the previous crop. Commercially acceptable fresh market yields were approached with both varieties and waters in spite of moderate salinity and sodium under heavy textural soil conditions, high temperatures and the presence of certain diseases in the area.

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The present study was carried out to determine the mechanisms of biological control of <i>Fusarium oxysporum </i>f.sp. <i>lycopersici </i>by <i>Brevibacillus brevis </i>under greenhouse conditions.  Dual culture techniques demonstrated that <i>B. brevis </i>is capable of inhibiting the growth of fungal mycelium and germination of fungal spores due to excretion of antifungal metabolite(s) into the substrate, while reciprocal <i>in vitro </i>tests demonstrated no impacts of <i>F. oxysporum </i>f.sp. <i>lycopersici </i>metabolites on viability of <i>B. brevis.  </i>When live tomato roots were introduced into microcosms containing <i>F. oxysporum </i>f.sp. <i>lycopersici </i>and <i>B. brevis,</i> however, the fungal pathogen showed a competitive advantage over controls without <i>B. brevis </i>in terms of host colonisation.  The steroidal glycoalkaloid α-tomatine, extracted from tomato, inhibited conidiospore germination and growth of <i>Fusarium oxysporum </i>f.sp <i>lycopersici,</i> but had no detectable effects on viability of <i>B. brevis.</i> The effects of preinoculation of tomato (<i>Lycopersicon esculentum, </i>variety Moneymaker) roots with <i>B. brevis </i>in presence and absence of <i>F. oxysporum </i>f.sp. <i>lycopersici</i> on the induction of defence enzymes was examined.  Varying activities of phenylalanine ammonia lyase (PAL), peroxidases (POX) and chitinases were observed in different treatments at different time points, suggesting that the genes encoding these enzymes play a role in defence against Fusarium wilt.  Although no direct evidence of induction of these enzymes by <i>B. brevis </i>alone was observed, plants which were preinoculated with the bacterium showed enhanced induction of PAL, POX and chitinases at different time points following subsequent inoculation with <i>F. oxysporum </i>f.sp. <i>lycopersici.</i> Complex interactions between the tomato plant, <i>B. brevis </i>and <i>F. oxysporum </i>f.sp. <i>lycopersici </i>occurred and changed with time, as indicated by variations in metabolites at different sampling times.

The auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) has a pleiotropic phenotype including a lack of lateral roots and reduced gravitropic response, apical dominance, vascular development, and fruit growth. The dgt mutation reduces the auxin sensitivity of only a subset of auxin responses while levels, metabolism, and transport of auxin appear normal, suggesting that the Dgt gene encodes a component in an auxin-signaling pathway. This dissertation reports isolation and characterization of the Dgt gene. Delineation of three microsyntenic regions in the Arabidopsis genome containing genes homeologous to genetic markers near the Dgt gene allowed isolation of additional ESTs from the corresponding tomato region, significantly reducing the mapping distance to the dgt locus. Further analysis determined that the Dgt gene encodes a cyclophilin (LeCYP1), a previously unidentified component of auxin signaling. Each known dgt allele contains a unique mutation in the coding sequence of LeCyp1. In addition, the wild-type Dgt gene can complement dgt mutant plants. Cyclophilins characteristically have peptidylprolyl cis-trans isomerase (PPIase) activity, but it is unclear whether that activity is necessary for all of their biological functions. Each allelic dgt mutation reduces or nullifies PPIase activity of LeCYP1 fusion proteins in vitro. Immunoblot analysis indicates that all three dgt mutations are null mutations. Phylogenetic comparisons of tomato and Arabidopsis cytosolic-type cyclophilins could not identify any single Arabidopsis member as orthologous to LeCYP1/DGT. Five T-DNA insertion mutants were analyzed to determine if mutations in Arabidopsis cytosolic-type cyclophilins phenocopy the pleiotropic dgt phenotype. Overall seedling growth and morphology appear normal in the mutants, however, their gravitropic response is slow. The lack of exact phenocopy may be due to the redundant nature of Cyp genes in Arabidopsis, which has over twice as many Cyp genes as tomato. In tomato, the cyclophilin inhibitor cyclosporin A (CsA) inhibits auxin-induced adventitious root initiation and expression of two early auxin response genes, LeIAA10 and 11, that are also affected by the dgt mutation. Taken together, these results suggest that the cyclophilin encoded by the Dgt gene plays an important role in auxin signal transduction. / Graduation date: 2004

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1984. / Vita. Abstract. Includes bibliographical references (leaves 40-42). Also available via the Internet.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 45 p. : col. ill. Vita. Includes abstract. Includes bibliographical references (p. 39-42).