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Studies on Diplodia and Diplodia-like fungi: VII. Criteria for classification
No full textVariation encountered in cultures resulting from single pycnidiospores of representative isolates of the Phaeodidymous: Sphaeropsidales was analyzed. Spore morphology, ornamentation, and size are proposed as the most stable characters for use in future taxonomic treatments of this group. The genus Diplodia is broadened to include all fungi that produce dark, two-celled spores within a pycnidium
Eutypa armeniacae in apricot: Pathogenesis and induction of xylem soft rot
No full textApricot pruning wounds made at all seasons of the year were susceptible to infection and canker formation resulting from mycelial inoculation with Eutypa armeniacae. Cambial inoculations resulted in comparatively little infection, and inoculations of the inner bark (phloem) were negative. Evidence indicated that the pathogen is inactivated in some infections, and thus sometimes is prevented from forming perennial, girdling cankers. Death of the pathogen did not appear to result from the action of other microorganisms. Invasion of the xylem by E. armeniacae resulted in the formation of gum plugs in some of the tracheary elements, and the development of hyphae in the lumens of vessels, fiber-tracheids, and ray parenchyma cells. The hyphae penetrated cell walls directly or through pits. In advanced stages of infection, the hyphae grew longitudinally within the secondary wall, especially of fiber-tracheids, where, presumably through enzymatic action, they caused the development of soft rot. This soft-rot condition appears to be responsible for the commonly encountered brittle nature of apricot branches killed by this pathogen. The ability of E. armeniacae to cause soft rot was demonstrated histologically, and by its capacity to cause weight loss in inoculated birch wood. The soft-rot phenomenon appears to develop late in the disease syndrone. In vitro studies indicated the ability of the pathogen to produce enzymes that degraded cellulose and xylan. Almond and peach trees were slightly susceptible when wounded tissues were inoculated with mycelia of the fungus
A lysimeter investigation of nitrogen gains and losses under various systems of covercropping and fertilization, and a discussion of error sources
No full textThe net gain or loss of soil nitrogen was studied in lysimeters at Riverside for ten years under four series of treatments: (1) fall applications of cereal straw (5,000 pounds per acre); (2) a mustard winter covercrop; (3) purple-vetch winter covercrop; (4) sweet-clover winter covercrop. In each series, one lysimeter was given no fertilizer, one 100 pounds, and one 200 pounds of nitrogen per acre per year as nitrate. A summer-harvested crop (first barley, later Sudan grass) was grown in all lysimeters. Total nitrogen and organic matter in the soil at the outset and at five-year intervals, amounts of nitrogen removed by cropping and leaching, and amounts added in seed, rain, irrigation water, and fertilizer were recorded
Phytotoxicity of hydrocarbons
No full textBenzene, cyclohexene, cyclohexane, n-hexane, and hexene-1 were applied to young carrot and barley plants as vapors diluted with air, and to Anacharis shoots and root and leaf segments of barley and carrot in aqueous solutions. The tetrazolium reaction and plasmolysis were employed as vitality criteria in the aqueous-solution tests
Nitrification of ammoniacal fertilizers in some California soils
No full textBecause of the manner in which ammonium fertilizers are applied and the tendency of the ammonium ion as well as of free ammonia to be absorbed at the point of contact with soil colloids, localized high concentrations are the rule rather than the exception. A concentration gradient is produced with a maximum along the line of application
Measurement of oxygen diffusion rates with the platinum micro-electrode: I. Theory and equipment
No full textIn 1952, E. R. Lemon and A. E. Erickson introduced a method for measuring the rate of oxygen diffusion to a small platinum wire electrode inserted into the soil. This was considered analogous to measuring the oxygen movement to a plant root that would be in the same position as the wire electrode
Effects of mix composition, fertilization, and pH on citrus grown in U.C.-Type potting mixtures under greenhouse conditions
No full textEffects of mix composition, fertilization, and pH on citrus seedlings grown in several U.C.-type potting mixtures in containers were studied over a 5-year period. The mixtures, consisting of fine sand, sphagnum peat moss, and redwood shavings consistently produced greater growth than did a mix containing clay loam, fine sand, and peat moss. Copper deficiency, often encountered in plants grown in soils and soil mixtures containing peat, could be prevented by the addition of CuSO4 to the mixtures. Availability of other micronutrients to the plants appeared to be influenced primarily by soil pH which could be changed by varying materials used in the added fertilizer solution. When the soilleachate pH was higher than approximately 7.0, plants exhibited more micronutrient deficiency leaf patterns and made less growth