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Feeding preferences of Coptotermes formosanus Shiraki were evaluated on 60 field-collected pecan Carya illinoinensis (Wangenh) cultivars. The Moneymaker cultivar of C. illinoinensis was most preferred by C. formosanus, and the degree of feeding on this cultivar was significantly different (P < 0.05) from all other cultivars tested. Creek was the least preferred cultivar, but the degree of feeding was not significantly different from other cultivars. There was a trend for lower consumption by C. formosanus on commercially versus native cultivars. In a multiple-choice test, the Desirable pecan cultivar, was significantly (P less than 0.05) more preferred than southern yellow pine (Pinus palustris), chinaberry (Melia azedarach), and the pecan cultivar, Barton, respectively. The significance is that Formosan termites fed on both pecan cultivars and southern yellow pine which is a commercially important wood. They also fed on chinaberry, which is a commonly used tree in landscape. Coptotermes formosanus were significantly (P less than 0.05) more attracted to green leaf material from the Creek cultivar as compared to the other 50 cultivars tested. However, the Creek cultivar was the least preferred in the consumption test. This suggested that Formosan termites may be attracted to pecan trees and chemicals associated with the wood. It is evident that Formosan termites feed on various types of pecans in agro-ecosystems, this may be attributed to leaf characteristics as well as other factors such as random foraging and swarming behavior. These results further demonstrate that pecan cultivars are at risk to C. formosanus feeding.

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Experiments were conducted with lettuce at the field and in the glasshouse at the Hatfield Experimental Farm, University of Pretoria. The objectives of the study were to evaluate the performance of selected crisphead lettuce cultivars in relation to yield and quality performance and to investigate which level of nitrogen can produce high quality transplants. In the lettuce cultivar trial, fifteen crisphead lettuce cultivars were grown, during March to May 2004. The experiment was laid out as a randomised complete block design with four replications. At harvest, the centre 20 plants were cut for yield determination and five uniform plants were then cut longitudinally for head quality characteristics. For each cultivar, compactness and uniformity were also evaluated and the number of days to maturity was recorded. Among the cultivars tested, the best yielding cultivars were Dual Purpose (46.8 t•ha-1), Great Lakes (45.8 t•ha-1), Mohawk (44.3 t•ha-1) and Victory (43.9 t•ha-1). Poor yielding cultivars were Taina (30.5 t•ha-1), Cannon (31.5 t•ha-1), Summer Time (32.1 t•ha-1) and Classic (33.2 t•ha-1). Del Rio was the best disease resistant cultivar, producing 100% marketable heads. All cultivars tested had good compactness and uniformity with the exception of Great Lakes 659. Early-maturing cultivars were ready 60 days after transplanting. Seeds of the lettuce cultivar ‘Aviram’ were sown, in the nitrogen nutrition of lettuce transplant’s trial. Two days after seeding, the seedlings were fertigated every second day by floating the trays in the plastic-lined tubs containing nutrient solution at 0, 30, 60,90 and 120 mg•L-1 N until field capacity was reached. Transplants produced with 0 N grew poorly, regardless of the sampling date. Nitrogen at 120 mg• L-1 improved the response of shoot growth, plant height and leaf area, but adversely affected root growth. In general, relative growth rate was improved while net assimilation rate was reduced as N level increased. Root: shoot ratio decreased with applied N. The largest values of root: shoot ratio were obtained with 0 N. Both specific leaf area and leaf area ratio increased with applied N. Leaf mass ratio improved, while root mass ratio was reduced as N levels increased. At 35 days after sowing, leaf tissue N increased from 0.43 to 4.15 mg•kg-1 with N applied. Only 25% of the plants produced without N could be pulled from the seedling trays, whereas 90% could be pulled when 90 mg•L-1 N was added. This work suggested that at least 90 mg•L-1N, supplied via floatation irrigation was required to produce a transplant with sufficient roots for ease of pulling. Applying 90 mg•L-1 N, resulted in improved root and shoot growth, resulting in high quality transplants. / Dissertation (M Inst Agrar (Horticulture))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

The battle of wheat against pests and pathogens can be strengthened by genetically engineering the wheat plant for disease tolerance, e.g. by enhancing the expression of chitinase and â-1,3-glucanase genes. In order to obtain this long-term goal, an efficient tissue culture system, as well .as an optimal transformation procedure, was produced. Fourteen spring and winter hard-red South African wheat (Triticum aestivum L.) cultivars were compared for their regeneration and transient anthocyanin expression efficiencies. Embryonic and non-embryonic callus, as well as plantlets were obtained from all the cultivars using a modified MS basal medium supplied with 5 mg/L BAP. The modified ML3 medium could not sustain callus or plantlet development from any of the cultivars. The cultivars exhibiting the most vigorous growth were 'Betta' Dn2 and 'Gamtoos' (spring wheat), and 'Palmiet' Lr29 and 'Tugela' (winter wheat). These cultivars are, therefore, the most suitable for tissue culture establishment. The particle bombardment system was efficiently optimised using the anthocyanin reporter gene cloned into the pHP 687 vector. It was found that the optimal distance between the micro-carrier assembly and target material should not exceed 13 cm. A helium pressure of 1 400 kPa produced the highest percentage of anthocyanin expression, the most foci per embryo/callus and the least amount of tissue damage. The age of the target material was found to be an important determining factor during bombardment and, thus, the age of target material should not exceed 3 weeks. The cultivars most suitable for transformation were 'Palmiet', 'Palmiet' Dn1, 'Palmiet' Dn2 and 'Palmiet' Dn5. Bombardment with small particles, namely 1 µm tungsten and 1 µm gold, resulted in efficient penetration of the target cells and relatively little tissue damage. This, in tum, enabled the bombarded tissue to express a high percentage of anthocyanin. If was further found that the cultivar bombarded is receptive towards the particles used. The material subjected to selection after bombardment should contain a large amount of cells transiently expressing anthocyanin. Plantlets could not be recovered from the material bombarded with anthocyanin since the applied selection procedure was too strict. Material bombarded with chitinase and J3-1,3¬glucanase are differentiating more efficiently and appears to survive the strict selection pressure. / Dissertation (MSc)--University of Pretoria, 2010. / Genetics / unrestricted