Tomato species and cultivars, Lycopersicon esculentum L. cv. Ailsa Craig and Solairo, differing in drought resistance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content when exposed to soil drying treatment (SD). Under SD treatment, the reduction in plant height, leaf length and leaf area has been attributed to the decrease in leaf water potential and relative water content. Stomatal conductance of Solairo cv. was more sensitive to SD treatment than Ailsa Craig cv. and ABA content was found to be higher in it's xylem sap. There is a strong relationship between soil moisture content and stomatal conductance, ABA content and leaf water potential for both cultivars.

MicroRNAs are short single stranded RNA molecules derived from longer precursors with a hairpin like structure. MiRNAs are taken up into a complex, which can then target mRNA for degradation. Mi.RNAs have been shown to play a role in plant development and stress responses. A novel tomato miRNA has been discovered in our group before I started my project. The secondary structure of the miRNA is unusual as it contains a 600nt intron which is spliced out. We discovered that the miRNA is differentially expressed within the leaves exhibiting a wave like pattern from the base of the leaf to the tip. There are similarities of the expression of this miRNA to sink-to-source transition suggesting that this miRNA may have a role in development from young leaves to mature leaves. The expression of this miRNA is highly increased when the tomato plant is grown in light conditions, and the longer un-spliced version of this miRNA is accumulated at a higher level in plants grown in dark conditions. Therefore we concluded that light controls the splicing of this miRNA. Furthermore looking at the wave-like expression of the miRNA within the leaves and the changes in expression with plants grown in light and dark conditions, it seems plausible that the miRNA is involved in the sink-to-source transition of leaves. Following this hypothesis several constructs of the miRNA have been produced which will be transformed into tomato to test this hypothesis. The discovery of this miRNA and the study of it so far have revealed many avenues of possible investigation. This miRNA seems to be integrally involved in plant growth and development. Further study would show how this miRNA functions in the plant, which may shed light on sink-to-source transition.

This study aimed to investigate and develop integrated crop management systems in organic glasshouse tomato production. The different management strategies that were used were tomato hybrid choice, grafting onto pest and disease resistant rootstocks, different fertiliser input types applied at several N-levels, steam disinfection of the soil substrate, chitin soil amendments and Milsana foliar disease control treatments. Four different experiments investigated the effects of these factors, as well as interactions between them, on the severity of a foliar disease Powdery mildew (Leveillula taurica), a soil-borne disease Corky root rot (Pyrenochaeta lycopersici) and nematodes infestation (Meloidogyne spp.). Tomato plant growth and yield parameters were also recorded in order to distinguish how the management practices that control plant pathogens affect growth and yield. Tomatoes are an important and significant source of nutrients and secondary metabolites which give a range of health benefits since many of the tomato micro constituents show antioxidative properties and have been linked with reduced risk of various forms of cancer and heart diseases. However, there is some evidence that the quality of tomato fruit is affected by hybrid choice, fertility management practices, grafting onto resistant rootstocks and the ripening stage at harvest. Therefore, tomato samples harvested from different trusses and at different ripening stages were analysed for quality parameters namely sugars, dry matter content and total antioxidant concentration. Of the two hybrids used in this experiment, Belladona plants grew slightly faster than 984 and produced many small fruit, while 984 plants produced fewer but bigger and heavier fruit. However, Belladonna and 984 did not show significant differences in their hydrophilic antioxidant activity although 984 fruit had higher sugar and dry matter content than Belladona fruit. Grafting onto the different rootstocks had beneficial effects on plant growth and reduced nematodes and corky root rot severity, but there were no significant effects on fruit antioxidants. The rootstock He-man F1 whilst shown to be more resistant against nematodes than R-5872 F1, was merely tolerant against corky root rot infection. On the other hand, the two rootstocks used had different effects on yield parameters. Grafting onto R-5872 F1 resulted in production of a larger number of smaller fruits, whilst grafting onto He-man F1 resulted in fewer, but bigger and heavier fruit.

Thesis (M.Sc. (Agriculture)) --University of Limpopo, 2009 / The purpose of the study was to assess nitrogen variability in tomato using the Remote Sensing Technique. The assessment was carried out through three growth stages (seedling, 50% flowering, and 50% fruiting stage). The GreenSeeker optical sensor unit that records NDVI values and total leafy nitrogen analyzer, “The Primacssn Nitrogen Analyzer,” was used in this study for data collection. Fertilizers were applied to the soil (Urea - 46% N, Superphosphate) every two weeks in the pots only for the treated experiment, and no nitrogen application for the untreated experiment. Tomato cultivars Flora Dade and Roma VF were used during the experimentation. The mean NDVI values for cultivars Flora Dade and Roma VF were 0.83 with N application. This value was 0.81 without N-application. The mean N-content for cultivars Flora Dade and Roma VF were 3.30 g/plant with N application. This value was 2.94 g/plant without N-application. The cultivar Flora Dade with N applied had higher N-content (3.38 g/plant) than the cultivar Roma VF with 3.22 g/plant when no N is applied across the three growth stages. The number of fruits’ means values at 50% fruiting stage for cultivars Flora Dade and Roma VF were 8.9 fruit per plant with N application. These mean values were 5 fruit per plant without N application. It was also evident that plants likely to have lower N content (untreated) had delayed maturation unlike those with nitrogen applied (treated), which had rapid/early maturation. Untreated plants took an average of 120 days till maturity, whereas the treated plants took an average of 100 days till maturity. Ground measurement of NDVI by the GreenSeeker sensor in this study showed potential for assessing nitrogen variability in tomato. / National Research Foundation

Thesis (M.Sc. (Crop Science)) --University of Limpopo, 2012 / Organic tomatoes are increasingly popular with larger market acceptance since organic farming uses limited or no artificial chemicals. Application of organic fertilisers such as cattle manure has potential to boost organic tomato productivity particularly under low input farming systems. However, information is required on the optimum level of manure application on different tomato cultivars to help emerging tomato farmers in South Africa. The objective of this study was to determine the relative response of yield and yield components among selected determinate and indeterminate tomato cultivars using different levels of cattle manure. Two separate field experiments were conducted at the University of Limpopo during 2007 and 2008 using a split plot design with three replications. Two sets of tomato cultivars were included in which one set consisted indeterminate types (Money Maker, Ox Heart and Sweetie) and the other determinates (Roma and Floradade). Cultivars were assigned as the main plot treatments with six rates of manure (0, 10, 20, 30, 40 and 50 in gram per plant) applied as the subplot treatments to each set. Results indicated significant interactions (P ≤ 0.01) between indeterminate tomato cultivars and levels of manure applied for fruit yield and fruit size in both experiments. Plant height showed variation from 78 to168 cm in Experiment I and 87 to 176 cm in Experiment II. During Experiment I fruit number varied from 23 to 91 per plant and 23 to 97 in Experiment II. Significant differences were detected among determinate cultivars on fruit yield varying from 7928 to 3 4705 kg per hectare during Experiment I and 3 169 to 2 9840 kg per hectare during Experiment II. Overall, the best level of manure for maximum fruit yield and greater fruit size was achieved at 40 g per plant in the indeterminate cultivar Sweetie. Conversely, the best level of manure for maximum fruit yield was achieved at 30 g per plant in determinate cultivar Roma. Thus, to achieve maximum yield, tomato growers could apply 600 and 800 kg per hectare manure on the determinate and indeterminate tomato cultivars, respectively. / the National Research Foundation (NRF)

Bibliography: leaves 133-152. / xi, 152 leaves : ill. (some col.), col. map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Studies biological relatedness of strains of tomato leaf curl virus and cross-interaction with the replication-associated protein requireed for DNA replication. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1997