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Effects of different bio-fumigants on the control of root-knot nematodes (Meloidoygne javanica).

Paskwavaviri, Netsai Sharon — 2018-01-01T00:00:00Z

Title: Effects of different bio-fumigants on the control of root-knot nematodes (Meloidoygne javanica). Authors: Paskwavaviri, Netsai Sharon Abstract: Root-knot nematodes are one of the major economically important pests causing yield losses of up to 80% in many regions of the world including Zimbabwe. Control of nematodes has been mainly based on use of synthetic nematicides and these have negative impacts on the environment, as a result there is growing interest in alternative methods of management that are economically viable and non-polluting such as Bio-fumigation. An In vitro experiment was carried out in the 2018/19 growing season at Horticulture research Centre to investigate the use of different bio-fumigants (Brassica juncea, Brassica carinata, purple stem Cleome gynandra and green stem Cleome gynandra) at varying rates of 3, 5 and 10grams on the control of root-knot nematodes. The experiment was laid out as a 4×3 plus 1 factorial arranged in a Compete Randomised Design (CRD) with 13 treatments replicated 4 times. Nemacure®400Ec at 0.5ml/10mls water was used as a positive control. 100 juveniles of Meloidogyne javanica pure culture was obtained from Tobacco Research Board and were exposed to the different treatments and data was collected on the number of dead juveniles and number of eggs. Results show that there was significant interaction (p≤0.01) on the effects of bio-fumigants and rates on nematode mortality Brassica juncea at 10grams recording the highest juvenile mortality when compared to other bio-fumigants. There was no interaction (p≤0.09) between bio-fumigant type and rates on number of nematodes eggs. However, there was significant (p≤0.01) difference on the effect of the individual factors on number of nematode eggs recorded. Brassica juncea recorded the least number of nematode eggs followed by Brassica carinata, purple Cleome gynandra and green Cleome gynandra respectively. There was significant (p≤0.03) difference on the efficacy of different bio-fumigants rates on number of nematode eggs with 10grams recording the least number of eggs. Volatile compounds (ITCs) Isothiocynates produced from the hydrolysis of glucosinolates in plant tissue could have contributed to juvenile mortality and reduction in number of eggs recorded. It can therefore be concluded that use of Brassica juncea at 10grams as a bio-fumigant could be an alternative way of controlling root-knot nematodes.

Genotype × environment interaction studies on the performance, adaptability and stability of pre- release flue-cured tobacco hybrid lines in Zimbabwe

Chikwature, Nyasha — 2018-01-01T00:00:00Z

Title: Genotype × environment interaction studies on the performance, adaptability and stability of pre- release flue-cured tobacco hybrid lines in Zimbabwe Authors: Chikwature, Nyasha Abstract: The nature and magnitude of the genotype × environment interactions is important to identify superior and stable genotypes under target environments. This will assist to maximize specific adaptation and to speed up the distribution of new cultivars to growers. Eleven pre-release flue cured tobacco hybrid lines were evaluated for yield and quality in four different tobacco growing regions thus, Kutsaga and Rusape representing the slow growing areas, Trelawney representing the medium growing areas and Tengwe representing the fast growing areas . The thrust of this study was to assess the stability and adaptability of these hybrid lines. KRK 26R was used as a positive check line because it is a cultivar that is adaptable and stable to a wide range of environments. The hybrid lines were raised with the new float tray system of seedling production and all cultural practises were done following the TRB handbook recommendations. Significant genotype × environment variations were observed among the hybrid lines. For the total saleable yield, environmental high significant difference was observed (P = 0.001), the study revealed that Tengwe had the best yield of 2755kg/ha, while, Kutsaga had the least yield of 1934kg/ha. For the grade index genotypic highly significant difference was observed (P = 0.001) with G9 outperforming all other test genotypes including the check line with an index of 61.74, while, G1 least performed with an index of 51.0. For the top grades proportion Genotype × Environment interaction was found and GGE biplot procedure was followed and results indentified the stability and adaptability of the performance of the hybrid lines. The GGE biplots indentified that G7, G8 and G11 as the high quality and stable genotypes. G1, G2 and G5 least performed and had low stability. It was observed that Kutsaga that is located in the slow growing areas as the ideal testing environment for these set of hybrids that were under test.

Analysis of phenolic compounds in Carica papaya, Zingiber officinale, Ipomoea batatas and Myrothamnus flabellifolius using RP-HPLC-UV/VIS-DAD, and in vitro evaluation of antifungal activity on plant pathogenic fungi of economic importance

Mwelasi, Phumelela Peace — 2015-01-01T00:00:00Z

Title: Analysis of phenolic compounds in Carica papaya, Zingiber officinale, Ipomoea batatas and Myrothamnus flabellifolius using RP-HPLC-UV/VIS-DAD, and in vitro evaluation of antifungal activity on plant pathogenic fungi of economic importance Authors: Mwelasi, Phumelela Peace Abstract: Agricultural pesticides use is rising in crop protection against plant invaders of which fungi are chief in reducing both yield quantity and quality. Botrytis cinerea, Rhizoctonia solani, Macrophomina phaseolina and Alternaria alternata are polyphagous fungi of economic importance with severe yield and quality losses worldwide. Environmental concerns on pesticide use and their resistance now on a worldwide scale. Extensive studies of plant secondary metabolites have not exhausted their potential use as natural crop proctetants. The antifungal activity of plant phenolic extracts: Carica papaya leaves and bark; Zingiber officinale rhizomes; Myrothamnus flabellifolius above ground parts; and Ipomoea batatas leaves were investigated on the plant pathogenic fungi. Methanol (80%) was used to extract phenolic compounds from dried samples. Qualitative and quantitative analyses of extracts were done through Reversed-Phase High Performance Liquid Chromatograph, Ultraviolet-Visible light Diode Array Detector (RP-HPLC-UV/VIS-DAD) analyses. In antifungal in vitro assays, Potato Glucose Agar (PGA) in petri dishes was incorporated with three concentrations 250 ppm,500 ppm and1000 ppm) of sample plant phenolic compounds and active ingredients of fungicides (as positive controls); the negative controls were incorporated with diluent used to reconstitute plant phenolic compounds. The study was laid in a 7 x 3 factorial treatment in a completely randomized design replicated three times with the two factors being plant phenolic extracts and extract concentration. A 6mm diameter disc of the 7-day old pure fungi culture cultivated on PGA was aseptically inoculated at the centre of the petri dish for each treatment and petri dishes incubated at 20±2°C (B. cinerea) and 26±2°C (R. solani, M. phaseolina and A. alternata). Mycelial growth (diameter) measurements (in mm) were taken at 24hour exposure and stopped upon full colony diameter (85mm) observation in the negative control plates. Quantitative RP-HPLC-UV/VIS-DAD analyses yielded a strong peak at a Retention Time (RT) =1.01min for Ipomoea batatas however this could not be elucidated. Other extracts produced nondescript chromatograms that were not similar to standard phenolic compounds RTs. There were significant differences (ρ ˂ 0.05) in Total Phenolic Content of plant phenolic extracts yields (mgGAE/g), 55.7±2.2, 7.0±3.3, 106.1±12.0, 33.5±3.4, and 41.9±1.5 for C. papaya leaves, bark, Z. officinale, M. flabellifolius and I. batatas respectively. Phytochemical test results were varied amongst plant phenolic extracts, mostly being positive. Antifungal in vitro assays, plant phenolic extract and extract concentraction interacted significantly (all ρ ˂ 0.05) at all the time intervals for all the species except for B. cinerea 96 hours interval where only the plant phenolic extract were significant (ρ ˂ 0.05) whilst there was no significant interaction of the two factors. The interaction of the two factors showed varied results in their inhibition of mycelial growth with differences amongst plant phenolic extracts and fungi species noted. Percentage Mycelial Reduction (PMR) varied amongst phenolic extracts and phytopathogenic fungi. Generally, the phenolic extracts showed less antifungal activity compared to the positive control treatments (fungicides). Carica papaya bark and Z. officinale rhizomes showed the highest PMR against M. phaseolina (30%≤PMR≤40%) at the 1000 ppm concentration. Z. officinale showed the highest PMR (45.3%≤PMR≤ 54.7%) for all the concentrations on A. alternaria. M. flabellifolius showed the highest PMR (26.5%≤PMR≤53.9%) for all the three concentrations on R. solani. Only M. flabellifolius had limited PMR of 0-5.9%, whilst other plant phenolic extracts showed a 0% PMR agaist B. cinerea. The result of PMRs shows that plant phenolic extracts have potential use in vivo as crop protectants however further research may consider reduced fungicide dosages by using both synthetic and plant phenolic extract as mixtures.

Effects of pine bark amended with goat manure as tomato (Solanum lycopersicon L) seedlings growing media using the float system

Madziwa, Munyaradzi — 2014-05-01T00:00:00Z

Title: Effects of pine bark amended with goat manure as tomato (Solanum lycopersicon L) seedlings growing media using the float system Authors: Madziwa, Munyaradzi Abstract: Pine bark is locally available in Zimbabwe and is widely in vegetable seedling production. However, it lacks essential nutrients for seedling growth. Goat manure was used to supplement nutrients when pine bark is used as growing media. The main object of the study was to determine the effect of pine bark amended with goat manure on tomato seedling emergence and seedling quality parameter which were stem diameter and stem length. The study was carried out at the Tobacco Research Board which is located 15 kilometers East of Harare at an altitude of latitude 170 55' S and longitude 310 08' E. The experiment was laid out in a 3 X 3 Factorial in a Completely Randomized Design with three replicates. The experiment had nine treatments with three different growing media which were un-amended pine bark, pine bark amended with goat manure and pine bark amended with Calcium carbonate (CaCO3). It also had three fertilizer rates which were 0 ppm, 75 ppm and 150 ppm float fertilizer. Results from this study showed that the different media and fertilizer combinations had a significant effect (P<0.05) on seedling emergence, stem diameter and stem length. From the results pine bark amended with goat manure significantly increase seedling emergence, stem diameter and stem length compared to un-amended pine bark and pine bark amended with CaCO3. A combination of pine bark amended with goat manure and 75 ppm float fertilizer had a significantly high emergence percentage, stem length and stem diameter compared to other media and fertilizer combinations.