The flue curing process for tobacco is practiced today in nearly the same manner as when tobacco first became of commercial importance, with no definite procedure being followed. A scientific study has proved that the curing process is accurately defined within narrow limits, and that control rather than art may be more definitely relied upon. Tobacco curing differs from a true drying process in that both physical and chemical changes are involved. Since it is impractical to evaluate the chemical changes because of their complexity, the physical changes were investigated, for they govern both the chemical and physical changes which take place. Drying rate curves for each period of the curing process were obtained over a wide range of constant conditions of temperature, relative humidity, and air velocity. Correlation of these curing curves indicate the narrow limits of the conditions required for satisfactory curing, and the critical points beyond which resulted in poorly cured tobacco. From the results obtained, air conditioning improves the process by (1) reducing the time approximately one-half, thus doubling the capacity of the barns; (2) the production of uniform quality tobacco completely eliminating loss from improper curing; and (3) large reductions in labor and fuel requirements. / Master of Science

Two flue-cured tobacco varieties (Nicotiana tabacum L.) and eight harvesting and curing methods were simultaneously evaluated. Harvesting variables involved the removal of different leaf numbers on different schedules. Curing methods included single or separate barn conventional curing and a bulk curing method. Certain agronomic, physical, and chemical factors were measured. The modified harvesting methods in which the leaves were removed in less than the conventional number of harvests caused a reduction in yield and value, but not in price. Bulk curing also resulted in lower yield and value per acre as well as dollars per hundredweight than conventionally cured leaves, but there were no differences associated with curing leaves from different stalk positions in separate barns. When considering stalk positions, modification of the harvesting methods from the normal method caused a reduction in yield and an increase in filling value for the lower leaves from each harvest section. Bulk curing caused an increase in filling value in comparison to conventionally cured leaves. Leaves from the modified harvest treatments were higher in amino nitrogen and lower in nicotine concentration than normally harvested tobacco. Leaf extracts were less acidic for leaves which were harvested in one day than for normally harvested leaves. With increases in stalk position, the nitrogenous factors and water soluble acids increased, while the pH value decreased. Reducing sugars were highest for midstalk tobacco and decreased in leaves from the extremities. Plants that were harvested three times were not greatly altered in agronomic, physical, or chemical factors from those harvested conventionally, but the bulk curing of the leaves (as operated in 1970) did alter these factors. / Master of Science

Research report presented to SBL, Unisa, Midrand. / There is a dearth of literature on how buyer-supplier relationships are organised in industries in developing countries. In this study, we drew on the existing theoretical framework on buyer-supplier relationships to establish the nature of buyer-supplier relationships in the Zimbabwean tobacco industry. Managers may use these findings as a foundation for further research on how these relationships can be improved and to gauge their current position to enable planning for strategic positioning in global competitive markets.

published_or_final_version / Dentistry / Master / Master of Dental Surgery

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From a cDNA library of potato tuber, cDNAs for the potato carboxypeptidase inhibitors were isolated and characterised by DNA sequencing. One full length clone of each type was used to make plant expression constructs, and these constructs used to transform tobacco. An insect bioassay, conducted using the self crossed progeny from the highest expressing transgenic line, revealed that the expression of potato carboxypeptidase inhibitor in tobacco increased the susceptibility of the plants to attack by Heliothm virescens .A cDNA library of whole Manduca sexta larvae was constructed in XZAP II. Oligos were designed to fit the strongly conserved region of insect haemolymph Q-ypsin inhibitor protein sequences and to a region of published protein sequence from Manduca haemolymph trypsin inhibitor A ( MHTl A ) and these were used to PGR a fragment of a MHTI A cDNA. This fragment was used to screen the cDNA library and a number of clones for MHTI A were isolated, along with cDNAs for a previously unknown related protein. These cDNAs were characterised by DNA sequencing. One of the MHTI A cDNAs was used to make plant and E. coli expression constructs and these were sent, for subsequent bioassays of the resultant transgenic plants and of bacterially expressed protein, to Horticulture Research International. While these assays were seriously flawed, there were strong indications from both the plant and the artificial diet bioassays that MHTI expression did enhance insect resistance. A cDNA library of whole Diabrotica undecimpunctata larvae was constructed in XZAP II. Oligos were designed to fit each of the three strongly conserved regions of protein sequence of mammalian and nematode microsomal aminopeptidases. These were used to PGR fragments from both Manduca and Diabrotica cDNA templates. These PGR products were characterised by DNA sequencing and the Diabrotica PGR products used to screen the cDNA library. Two cDNAs were isolated, neither of which were full length, but which were of sufficient length for protein expressed from them to be likely to be functional as an aminopeptidase. E. coli expression constructs were made from each cDNA and bacterial expression was demonstrated. Pilot work on the feasibility of using antibodies as anti-insect proteins was conducted and the antibodies shown to be reasonably resistant to Diabrotica gut proteases. It was also demonstrated that antibodies could be produced that were active at the extreme pHs (3.5- 11) found in insect guts. While many questions have been left unanswered, this project has successfully demonstrated the viability of such novel approaches to the enhancement of insect resistance in plants by genetic engineering.