Thesis (M.A. Agricultural Management (Plant Production)) -- University of Limpopo, 2015 / Tomato (Solanum lycopersicum L.) production had been ranked as the most important commodity in terms of job and wealth creation within the auspices of the National Development Plan (NDP) framework in Limpopo Province. However, soil-borne diseases including plant-parasitic nematodes preclude the successful monoculturing of this commodity and therefore inducing instability in job creation. Generally, after growing a tomato crop for one season in commercial tomato-production systems, the land is being fallowed for 3-5 years under natural grasses. Attempts are being initiated to ensure that during the 3-5 years the land be occupied by an economic alternative crop in order to level off job instability as broadly articulated in the NDP framework. The production of sweet stem sorghum (Sorghum bicolor L.) for ethanol production during the 3-5 years fallowing period could potentially be attractive to commercial tomato-producing famers. Preliminary agronomic evaluations demonstrated that sweet stem sorghum var. ndendane-X1 had attributes to fulfil the identified need. However, the degree of nematode resistance of the variety to Meloidogyne incognita race 2 and M. javanica, which are dominant in Limpopo Province, along with the compatibility of var. ndendane-X1 to phytonematicides used in tomato production had not been documented. The objectives of the study were, therefore, to determine whether sweet stem sorghum var. ndendane-X1: (1) had any degree of nematode resistance to M. incognita race 2 under both greenhouse and microplot conditions, (2) had any degree of nematode resistance to M. javanica under greenhouse conditions, and (3) would be compatible with phytonematicides used in suppression of population densities of xiv Meloidogyne species in tomato production under field conditions. In the greenhouse trials, seeds were sown in 20-cm-diameter plastic pots and each seedling inoculated with 0, 600, 1 000, 1 400, 1 800 and 2 200 eggs and second-stage juveniles (J2s) of M. incognita race 2 or M. javanica. Treatments were arranged in a randomised complete block design (RCBD), with 10 replicates (n = 60). In the microplot trial, seeds were sown in 30-cm-diameter plastic pots and buried 75% deep in a 0.30-m intra-row and 0.25-m inter-row spacing. Treatments, namely, 0, 200, 600, 1 000, 1 400, 1 800 and 2 200 J2s of M. incognita race 2 were arranged in RCBD, with 14 replications (n = 98). In a Meloidogyne-infested field trial, seeds were sown at 0.2-m inter-row and 0.3-m intra-row spacing, with treatments 0, 2, 4, 6, 8 and 10 g nemafric-BG phytonematicide/plant, arranged in RCBD, with 13 replications (n = 78). The degree of nematode resistance was measured using host-status and host-sensitivity, which provide information on reproduction of the target nematode and plant damage due to nematode infection, respectively. Nematode reproduction was measured through the reproductive factor (RF), which is a proportion of final nematode population density (Pf) to initial nematode population density (Pi), summarised as RF = Pf/Pi. In all nematode resistance trials, RF was equivalent to zero, which implied that var. ndendane-X1 was a non-host to both M. incognita race 2 and M. javanica. Additionally, in both greenhouse and microplot trials, sweet stem sorghum var. ndendane-X1 did not suffer any significant damage due to infection by Meloidogyne species. Using nematode-plant relation concepts, sweet stem sorghum var. ndendane-X1 was resistant to M. incognita race 2 and M. javanica under greenhouse and microplot conditions. Under field conditions, nemafric-BG phytonematicide reduced eggs and J2s of Meloidogyne species in root and soil samples xv by 76-85% and 24-65%, respectively, without nematode effect on plant growth, suggesting that nemafric-BG could be integrated with nematode resistance in var. ndendane-X1 to manage nematode population densities. In conclusion, pilot projects where sweet stem sorghum var. ndendane-X1 could be used during the 3-5 years fallowing period in a tomato-sweet stem sorghum crop rotation system should be established to assess: (i) the economics of the proposed cropping system, (ii) the effect of the cropping system on soil-borne diseases, including plant-parasitic nematodes, and (iii) the effect of the cropping system on soil health.

Lycopersicon esculentum Mill. cv. Rodade was developed in South Africa for the fresh produce market. This cultivar is also of major importance for South African tomato breeding programmes because of its resistance to bacterial wilt. In this study, aspects of the effects of 6-benzyladenine on adventitious shoot formation by both L. esculentum cv. Rodade and Lycopersicon peruvianum Mill. were studied in vitro. These included the regeneration of adventitious shoots, the effects of different incubation times, the uptake and metabolism of BA and the effect of auxin on the metabolism of BA in both leaf and callus tissue of the two species. Adventitious buds could be regenerated on all tissue types except for callus tissue of L. esculentum. A stepwise increase in the percentage shoots produced was observed indicating a period of induction wherein incubation on a medium containing BA is beneficial to the production of shoots. Leaf tissue was more responsive to BA treatments than callus tissue of both species. The main route of BA metabolism in both species is from BA to [9R]BA and [9R-MP]BA. Callus tissue of L. esculentum cv. Rodade however converted BA to the 3- and 9- glucosides of BA rather than to metabolically active forms of the cytokinin. The auxin, indole-3-acetic acid, played a definite role in the conversion of BA to [3G]BA and [9G]BA in leaf tissue of the tomato cultivar tested, but had no effect in callus tissue of this species. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1993.

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