Tubers of Russet Burbank were surface disinfested and 3 mm diameter by 3 mm deep wounds were made with cork borer. The holes were inoculated with 20muL of 104 macroconidia/ml suspension of (Fusarium sambucinum) or 20muL of 104 sporangia/ml suspension (Pythium ultimum) and incubated under mist. For infection studies, the inoculated tubers were exposed to 0--48 h of mist at 4--20ºC, dried and stored at 16ºC and 95% RH in growth chamber with forced air for 15 d (F. sambucinum), whereas stored at 12ºC and 95% RH for 30 d (P. ultimum). For lesion expansion studies tubers exposed to 24 h wet at 16ºC were stored in growth chambers at 4, 8, 12, and 16ºC for 15--90 d. At the end of storage tubers were cut and the volume of diseased area was measured. Models explained 94.2% of the variation in infection and 99.7% in lesion expansion for F. sambucinum . Whereas, models explained 96.7% of the variation in infection and 99.6% lesion expansion for P. ultimum. (Abstract shortened by UMI.)

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Call number: LD2668 .T4 1985 L33 / Master of Science

The potential of hot water dipping, vapour heating or ultraviolet irradiation to eliminate the use of chemicals for control of sprouting and post-harvest diseases of the potato (Solanum tuberosum L.) was examined. The microorganisms on which these treatments were tested were the fungal dry rot (Fusarium solani) and the bacterial soft rot (Erwinia carotovora pv. carotovora), two major post-harvest pathogens of potatoes. The study focused on short-term storage (three months) at 8$ sp circ$C or 18$ sp circ$C, which are representative of storage temperatures used by producers in northern temperate and semi-arid tropical regions, respectively. / Response surface methodology was used in experimentation to facilitate analysis of data and identification of optimal operating conditions for the treatments. The following parameters were used to assess tuber quality after the treatments and 3-month storage: firmness, color and structure. / It was found possible to obtain 100% control of sprouting and diseases for the three-month storage without resorting to the use of chemicals. This was achieved without significantly altering the quality attributes of the tubers under certain conditions of hot water, ultraviolet radiation or combinations of these two with storage at 8$ sp circ$C for three months. Although 100% control was not possible for the storage at 18$ sp circ$C, treated tubers performed much better than the controls. Vapour heat (50-70$ sp circ$C) was much less effective at controlling sprouting and was therefore not tested on the pathogens. / A numerical model of the heat transfer phenomenon in the tuber was also developed. It was used to predict the transient temperature distribution in the tuber. The model was solved using the line-by-line technique and model simulations were validated against experimental data.

Much research has proven that computer controlled vegetable storage can achieve better storage conditions than traditional control systems. During the last 10 years, the use of microcomputer-based environmental control systems has become commonplace. However, to take full advantage of this computerization of the control process, it is not enough only to program the control functions that are performed by normal analog equipment. New and better control strategies must be developed. Recent advances in computer technology have made possible the development of expert systems; a branch of artificial intelligence. One of the advantages of developing such a system is that it provides a reasoning tool which approaches the level of proficiency human experts exhibit in that field. The application of new control methods using expert systems has been extensively demonstrated for greenhouse environments. However, the application of expert systems for the control of vegetable storage is still to be investigated. In the first phase of this project, the development and implementation of a sophisticated control software, using a conventional algorithm-based programming language, were achieved. Throughout the three years of experimentation in an industrial potato storage, the software proved to be appropriate for the control of storage environmental parameters (temperature and relative humidity). During the second phase, the application of an expert system for the on-line control of potato storage was explored. The development of a rule-based expert system, that could replace the conventional algorithm-based control routines was achieved. The integration of the expert system into the control software will result in a highly efficient control software, which can easily be maintained and improved as new knowledge emerges. The use of an expert system will also render possible the representation of heuristic knowledge in the form of rules, which was not possible with the use of conven

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Please read the abstract in the section 00front of this document. Also note that an abstract is provided for each chapter as well / Thesis (DPhil (Entomology))--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

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