Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

A commercial extract of kelp, Ascophyllum nodosum (L.) LeJolis, was applied as a foliar spray on third and fourth cutting alfalfa (Medicago sativa L.) in fertilized and nonfertilized plots. Kelp treatments alone had no effect on alfalfa yield and quality, on tissue levels of nitrogen, phosphorus, and potassium, or on populations of potato leafhopper (PLH), Empoasca fabae (Harris). For the fourth cutting, fertilizer and kelp*fertilizer effects were observed. Yield and tissue levels of potassium were higher and PLH numbers were lower in fertilized plots. In fertilized plots, kelp temporarily reduced numbers of PLH adults one week after kelp treatment, followed by lower numbers of PLH nymphs. In nonfertilized plots, PLH adult levels were initially higher, followed by increased numbers of nymphs. The number of fungal leaf spots on the top five leaves was lower on fertilized plants than on nonfertilized plants, on kelp-treated plants in nonfertilized plots, and on plants treated with the insecticide dimethoate compared to nontreated plants. Extracts of kelps, A. nodosum and Durvillea potatorum (Labill.) Aresch., were applied to cantaloupe (Cucumis melo L.) plants grown under three nutrient regimes. Kelp treatment lowered the tissue concentration of total nitrogen in one instance, but had no effect on nitrogen deficiency symptoms which were present in all plants. Kelp treatment slightly reduced phosphorus and increased boron and magnesium concentrations in plant tissue. Both kelp sprays increased dry root weights; A. nodosum also increased dry shoot weights and root:shoot ratio; D. potatorum decreased root rot. These kelp effects were most prominent in plants receiving the mid-level nutrient concentration. / M.S.

The application of seaweed concentrates to plants has been shown to enhance growth and improve yield parameters. How these natural products elicit their beneficial responses is still unclear. While many of the growth responses have been attributed to cytokinins, it is obvious that this group of plant hormones cannot account for all the beneficial effects incurred from seaweed use. This study was therefore initiated to investigate the effects of a commercial seaweed concentrate (Kelpak) on several aspects of plant growth and development. Tentative determination of plant growth regulators in the seaweed concentrate (SWC) using bioassay systems, indicated the presence of compounds with gibberellin- , abscisic acid- and auxin-like properties. Tentative identification of the auxins present in the SWC and Ecklonia maxima using High Performance Liquid Chromatography revealed the presence of tryptophan, indole-3-acetamide, indole-3- acetic acid, indole-3-carboxylic acid and indole-3-acetaldehyde. The effect of SWC on the growth of nodal potato explants cultured in vitro was examined. 0.2% SWC significantly accelerated shoot growth and development. When applied at a concentration of 0.4% the number of axillary shoots per node increased. This treatment also stimulated the development of potato tubers on the shoots. The SWC was also shown to enhance the growth of tomato (Lycopersicon esculentum Mill.) roots cultured in vitro. Filtration of the SWC indicated a promotory filtrate phase and an inhibitory cell wall phase. ' The application of the SWC to nematode-infested roots, cultured in vitro, reduced the degree of infestation In susceptible roots but induced host/parasite compatibility in a resistant variety. One of the most pronounced effects noted with seaweed application was the promotion of adventitious roots on several species of garden plants. The application of similar dilutions to Eucalyptus cuttings increased the average root mass but had little effect on the number of roots initiated per cutting. The rooting factors, purified by HPLC, were tentatively identified as indole-3-acetamide, indole-3-acetic acid, indole-3-carbo. xylic acid or indole-3-acetaldehyde by co-chromatography with authentic standards. Finally, the effect of seaweed concentrate on the growth of tomato plants grown in nematode-infested soil was investigated. SWC applied as a soil drench, improved plant vigour, significantly increased shoot and root fresh weights and resulted in a marked reduction in the number of nematode galls per unit length and per unit weight of root. Plants treated with a foliar spray of SWC were invariably the first to produce ripe fruit. Total yield was improved by over 10%. Ashing the SWC indicated that the active constituents are possibly of an organic nature. Filtering the SWC confirmed earlier reports that promotory and inhibitory compounds are present in the concentrate. Chromatographic separation of the SWC into 10 Rf zones indicated the presence of several components with growth regulatory properties. It was found that the same fractions that improved plant growth also reduced nematode infestation. The significance of these findings and the possible relationship between the endogenous plant growth regulators in Ecklonia maxima and the effect of the SWC on plant growth is discussed. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1990.

A preliminary experiment was conducted to determine the effects of salinity and moisture stress on the pathogenicity of root-knot nematodes (RKN) in turfgrass plants. The results indicated that RKN infection adversely affected both visual and functional parameters of bentgrass. Salinity and moisture stress further exaggerated the damage caused by RKN. Under well-watered conditions, the effects of SWC and RKN infection on bentgrass plants were studied. Applications of Swe at 0.5 liter ha⁻¹ and 1.0 liter ha⁻¹ effectively enhanced bentgrass growth under both RKN-free and RKN-infected condition. It was shown that RKN caused less damage to SWC-treated plants than to non-treated plants. In addition, a soil drench of 0.5 liter ha⁻¹ and 1.0 liter ha⁻¹ at 10 day intervals was required to enhance bentgrass growth under RKN-free and RKN-infected conditions, respectively. The effects of seven SWC treatments on the growth of nematode-free and RKN infected bentgrass plants were tested under three irrigation regimes. Rooting and leaf moisture parameters, quality and clipping yield were all improved to some degree by SWC applications. High dosage SWC treatments, applied as a soil drench at one liter ha⁻¹ every 10 days, were most effective in improving plant growth. Application of SWC was more beneficial to RKN-infected plants than RKN-free plants, and to abiotically stressed plants than to abiotic stress-free plants. In a separate study, seaweed application was also shown to enhance both top growth and root growth of lance nematode (Hoplolaimus galeatus) or RKN infected bentgrass grown under drought or salinity stress condition. With SWC application, almost all of the symptoms caused by nematode infection and the abiotic stress were partially overcome. In addition, root development, leaf water status and clipping yield were all improved. It was apparent that soil drench SWC treatments were more effective in enhancing bentgrass growth than foliar Swc treatments. Application of SWC slightly reduced the number of nematodes per unit of fresh root (for RKN) and per unit weight of soil (for lance nematodes). Protein extracted from SWC-treated or non-treated ryegrass plants under different stress conditions indicated that SWC altered plant protein synthesis, possibly by inducing selective gene expressions. / Ph. D.