Call number: LD2668 .T4 1958 Y8

Call number: LD2668 .T4 1965 S623 / Master of Science

Call number: LD2668 .T4 1966 N156 / Master of Science

Thesis (PhD(Agric) (Horticulture))--Stellenbosch University, 2008. / Lack of winter chilling is a major problem in producing temperate-zone fruit in warm climates. Delayed foliation and protracted bud burst and flowering are the main problems necessitating artificial means to break dormancy. In South Africa (SA), most apple production areas receive insufficient winter chilling, and an annual application of rest breaking (RB) agents is included as standard practice. The most used RB agent in SA was dinitro-o-cresol (DNOC) but its use was discontinued. Hydrogen cyanamide (HC) became the replacement. It has been effective in apple, but variable effects on fruit set, blossom, yield and fruit quality have been reported. Thidiazuron (TDZ) has also shown the ability to break dormancy in apples. Another important practice in apple production is chemical thinning (CT). However, results are highly influenced by the type of chemical, weather conditions, cultivar and blossom pattern. With the increasing efficacy of RB and by identifying its effects on vegetative and reproductive development, it will be possible to determine more effective chemical thinning treatments. The objective of this study was to determine appropriate RB treatments for apple trees in a warm winter climate, identifying their effect on vegetative and reproductive development and the influence on CT efficacy. The research was performed in the Elgin area (34°S, 300 m) SA, over a period of three years, on ‘Golden Delicious’ and ‘Royal Gala’. In evaluating the effect of different HC concentrations and oil, no synergistic or antagonistic effects were observed on budburst and yield. Mineral oil at 4% plus 1 to 2% Dormex® combined were sufficient to break dormancy. Dormex® at 4% (2.08% HC) reduced fruit set and yield. In general, the rest breaking treatments (DNOC, HC and TDZ) enhanced the final vegetative bud burst compared to the control, while reproductive bud burst in 2002 and 2003 was not significantly influenced. The treatments compressed and advanced flowering periods, but this effect was not always evident when the spring was warm. The treatments synchronised flowering on the tree and between the two cultivars. The mixture of 0.245% HC and 4% oil was less effective in terms of increasing bud burst in ‘Royal Gala’ compared to other rest-breaking treatments. The mixture of 0.49% HC and 4% oil effectively compressed and synchronised flowering in ‘Golden Delicious’. TDZ-oil used at the lower rates also increased bud burst and concentrated flowering. However, it appears that after a cooler winter, higher rates could result in an exacerbated bud burst effect with excessive vegetative growth. The rate and timing of TDZ-oil application influenced the reproductive development of apples and therefore fruit quality. In ‘Golden Delicious’ increased fruit set, number of seeds, and reduced fruit russeting appear as beneficial results of TDZ-oil, whereas fruit set and russeting was not affected in ‘Granny Smith’. TDZ-oil, when applied late and at increasing rates, led to an increase in the malformation of calyx cavities, especially when chemical thinning was performed using the cytokinin-like compound benzyladenine. The effect seemed to be cultivar specific, with ‘Golden Delicious’ being the most severely affected. Increased return bloom in response to late TDZ application in ‘Golden Delicious’ and ‘Royal Gala’ appeared to be beneficial.

Two areas of research are reported: an experiment on the effects of warm temperature prestratification treatments on seed dormancy and a new chill unit model. Crabapple seeds (Malus sargentii Rehd.) were allowed to imbibe water and were given warm pretreatments at temperatures of 16, 20, 24 and 28C for periods of 3, 10, 20 or 30 days before cold stratification at 4C for 20, 40, 60, 80 or 100 days. Pretreatments resulted in increased chilling requirements for seedling emergence. A short chilling period (20 days) also altered the leaf area, shoot length, internodal length and root/shoot ratio of the resulting seedlings. The new chill unit model was developed from data from seed experiments and tested with records of 11 years. A three-dimensional model for the transition through apple tree dormancy is proposed. The new model evaluates the effectiveness of different temperatures for the transition between dormancy induction and dormancy release according to physiological time. The standard of measurement for this model is the chill unit (CU), which is defined as the equivalent of one-hour exposure to the optimal temperature during the optimal physiological time for dormancy development. The general pattern of temperature activity for dormancy development is sigmoidal; and temperature effectiveness through the process varies according to length of exposure, temperature cycling and time. The new model permits a more accurate prediction of dormancy development under subtropical conditions than previous models and will predict the amount of leafing that will occur in spring. The prediction efficiency of leafing under subtropical conditions was improved from an r2 of 0.66 for the Utah Chill Unit Model to an r2 of 0.74 for the new model when compared under Mexican conditions.

Dissertation (Ph. D.)--University of Akron, Dept. of History, 2009. / "May, 2009." Title from electronic dissertation title page (viewed 11/27/2009) Advisor, Kevin Kern; Committee members, Lesley J. Gordon, Kim M. Gruenwald, Elizabeth Mancke, Randy Mitchell, Gregory Wilson; Department Chair, Michael M. Sheng; Dean of the College, Chand Midha; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 358-375).

Animal population ecology has become a rapidly expanding natural science over the past decade. This trend is the result of many interacting factors, not least among them being; the maturation of ecology from a more or less descriptive and a priori science to the beginnings of a quantitative, deductive-inductive approach; and, the need for a better understanding of the effect of pesticides and biological agents on the trend of pest populations. Such knowledge is almost completely lacking, although the work in Canada of R.F. Morris, E.J. LeRoux and their associates forms the basis of such a need. Obviously any quantitative study aimed at understanding the dynamics of any animal population, and hence the causes that account for changes in the rise and fall of such a population, must be a valuable addition to knowledge on this subject. [...]

The quantification of population and mortality data for insect pests of apple is necessary if we are to gain fundamental insight in the dynamics of insect populations of the orchard ecosystem. The need to quantify has recently been emphasized (LeRoux, 1964a; 1964b) and the greater application, practical and scientific, or the quantitative results obtained for agricultural and forest insect pests has been demonstrated (LeRoux et al., 1963). [...]

Polyphenol oxidase (PPO) enzymatic extracts were recovered from apple fruit and potato tubers and enriched by an acetone precipitation. The enriched PPO extracts were immobilized by adsorption onto a wide range of inorganic supports, including chitin, alumina oxide, glass beads, Celite, Dowex and Silica gel using selected media, including water, sodium phosphate buffer and a ternary micellar system. The highest immobilization efficiencies and specific activities were obtained when the PPO extracts were suspended in sodium phosphate buffer and adsorbed onto alumina oxide. Biocatalysis of the free and immobilized PPO extracts was investigated in selected organic solvent media, including hexane, heptane, toluene and dichloromethane, using chlorogenic acid, catechin, and the endogenous phenolic compounds from apple fruit and potato tubers as substrate models. In the organic solvent media, the free PPO extracts from apple and potato demonstrated optimal enzymatic activities at 28°C and between 25 to 35°C, respectively, whereas the immobilized extracts both showed optimal enzymatic activities at 30°C. The free and immobilized extracts from apple and potato also showed similar pH values for optimal enzymatic activity in the range of 6.0 to 6.5. The immobilized apple and potato PPO extracts demonstrated a 1.5 to 1.8 and 2.1 to 3.2-fold increases in PPO activity, respectively, compared to those observed with their free counterparts, and the lowest Km values were obtained with chlorogenic acid followed by catechin and the endogenous phenolic compounds. The immobilized and free PPOs from apple and potato also showed higher Vmax values in the hexane medium followed the heptane, toluene and dichloromethane media. The end products of PPO biocatalysis were purified by size-exclusion chromatography and detected at 280 nm for the residual catechin and endogenous phenolic compounds, and at 320 nm for the PPO-catalyzed end products. Spectroscopic scanning