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Mayashree Chinsamy, Manoj G. Kulkarni and Johannes Van Staden

Abiotic stresses negatively affect the rate of nutrient mobilization in soils resulting in poor crop performance. Vermicompost-leachate (VCL) is an organic liquid produced from earthworm-digested material. It improves soil fertility as a result of the presence of proteins, vitamins, and micro- and macroelements. However, the effects of VCL on plant growth under temperature and water stress are not yet fully studied. To assess the growth performance under low, optimum, and high temperatures, 1-month-old well established tomato seedlings were treated with and without VCL (1:10 v/v) under various temperature regimes (10, 15, 20, 25, and 30 °C). In the second trial, tomato seedlings were tested in a greenhouse with and without VCL (1:10 v/v) at different watering regimes (15, 30, and 45 mL of Hoagland’s nutrient solution) to evaluate the effect of water stress. In comparison with the control seedlings, VCL treatment significantly improved stem thickness, leaf area, and shoot/root both fresh and dry weight of seedlings at 30 °C. At this temperature, VCL-treated seedlings showed a significant increase for all examined physiological parameters (total chlorophyll, total sugars, and proline). Number of leaves, stem thickness, and shoot/root length and fresh weight of VCL-treated tomato seedlings irrigated under a low watering regime were significantly greater than the control. Total chlorophyll, total sugars, and proline content were significantly elevated at the high watering regime but declined in the low watering regime with VCL treatment. Both increasing and decreasing trends of compatible solutes and photosynthetic pigments indicated osmotic adjustment to stress conditions. VCL can be a suitable soil amendment product to improve overall soil fertility and, more importantly, growth of tomato plants even under temperature and water stress conditions.

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Dave I. Thompson, Neil O. Anderson and Johannes Van Staden

Polyploidy represents a useful tool for increasing marketability of floriculture crops. The efficacy of 250 μM colchicine [0.01% (w/v)] as a means of inducing polyploidy in six South African Watsonia species (W. borbonica subsp. ardernei, W. humilis, W. laccata, W. lepida, W. pulchra, and W. vanderspuyiae), as determined through high-resolution flow cytometry, is reported. Exposure to colchicine during imbibition and as 24-, 48-, or 72-h pulse treatments for in vitro-germinated seeds resulted in seedlings with increased ploidy, reaching a maximum of 60% induction after the 72-h pulse treatment. The greatest proportions of induced individuals from both the pre- and post-germination exposure treatments were of mixed ploidy. These mixoploids were induced in five species. Non-chimeric tetra- and octaploids were produced in low frequencies only for W. vanderspuyiae during radicle-pulse exposure of 24 and 48 h. Increasing colchicine exposure at radicle emergence manifested as aberrant phenotypic expression and was typified by a reduction in leaf length and rooting capacity in vitro coupled with overall slowed growth. In vitro regeneration and multiplication is easily achievable for the genus and should allow for the capture and refinement of desirable polyploid tissues.

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Manoj G. Kulkarni, Glendon D. Ascough and Johannes Van Staden

Smoke shows promising results in stimulating germination and vigor. The biologically active butenolide compound isolated from smoke has potential to become a valuable tool in horticulture. ‘Heinz-1370’ tomato (Solanum lycopersicum) seedlings showed a positive response to smoke and were therefore tested with smoke-water and butenolide for growth, yield, and nutritional composition. Smoke-water (1:500, by volume) treatment showed the maximum height, number of leaves, and stem thickness from 57 to 78 days after sowing. The percentage of plants with fruit from 85 to 95 days after sowing was much higher with the application of smoke-water and butenolide solution than in the control. The total number of marketable fruit was significantly greater (P ≤ 0.05) for smoke-water–treated (1:500, by volume) tomato plants (168) than for the control (124). Butenolide and the lower concentration of smoke-water (1:2000, by volume) yielded more fruit, but was not significantly (P ≥ 0.05) different from the control. In spite of achieving a greater number of fruit, smoke treatments did not significantly (P ≤ 0.05) change the size, weight, and nutritional composition (ascorbic acid, β-carotene, lycopene, and total soluble solids) of fruit. The harvest indices of smoke-water– and butenolide-treated plants significantly improved (P ≤ 0.05), suggesting the possible use of smoke technology for tomato cultivation.

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Glendon D. Ascough, Johannes van Staden and John E. Erwin

Genetic modification and manipulation offers the possibility of introducing novel traits into existing plants, thereby increasing marketability. Polyploid induction has in the past produced plants that are more compact and have larger flowers, leaves, and fruit, making them more desirable to consumers. The effect of pulse treatments (0, 24, 48, and 72 h) of colchicine (25, 50, 125, and 250 μm) or oryzalin (30, 60, 90, and 120 μm) on in vitro-grown Watsonia lepida N.E. Brown shoots was investigated. Explant survival was higher and more consistent with oryzalin treatment compared with treatment with colchicine. More mixoploids than tetraploids were produced with both compounds. The optimum treatment for producing tetraploids was 120 μm oryzalin for 24 h. Of the 30% explants that survived this treatment, 33% were found to be stable tetraploids.

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Manoj G. Kulkarni, Glendon D. Ascough and Johannes Van Staden

The ecologic significance of smoke-related seed germination is now well recognized. Consequently, smoke solutions and a pure butenolide, the active compound from smoke that stimulates germination of a number of plant species, show great potential for enhancing the growth of vegetable crops. Achieving maximum production and better and faster growth of the seedlings has always been a priority for vegetable growers. This study therefore highlights the effects of foliar application of smoke-water and a butenolide on seedling growth of okra [Abelmoschus esculentus (L.) Moench] and tomato (Lycopersicon esculentum Mill.). Treating okra seedlings with smoke-water (1:500 v/v) showed a significant (P < 0.05) increase in shoot/root length, shoot fresh/dry weight, number of leaves, total leaf area, and stem thickness compared with the control treatment. Treatment of okra seedlings with smoke-water significantly (P < 0.05) increased the absolute growth rate (AGR) per week. However, the seedling vigor index (SVI) did not improve as a result of no change in root fresh weight. On the other hand, foliar application of smoke-water and butenolide showed a pronounced effect on the seedling growth of tomato. Most of the growth parameters examined for both the treatments were significantly (P < 0.05) increased, resulting in a significantly (P < 0.05) higher SVI and AGR than the control. This study indicates that the foliar application of smoke-water or butenolide may be a useful and inexpensive technique for enhancing seedling growth of vegetable crops.

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Michael W. Bairu, Manoj G. Kulkarni, Renée A. Street, Rofhiwa B. Mulaudzi and Johannes Van Staden

A study was done to investigate the effects of some physical and chemical factors on growth and development of Aloe ferox ex vitro and in vitro. The effects of light, temperature, and smoke–water on seed germination, ex vitro seedling growth requirements, and effect of germination medium and cytokinins on shoot induction and multiplication in vitro were investigated. The highest germination percentage of A. ferox seeds was recorded between 15 and 30 °C. Seed germination was inhibited at 10 and 35 °C. There was a nonsignificant increase in germination percentage (78%) for seeds that were germinated under constant dark conditions. Smoke–water-treated seeds showed significant improvement in percentage germination (80%) over the control (66%) at 25 °C with a 16-h photoperiod. Seedlings of A. ferox subjected to alternating temperatures (30/15 °C) or being irrigated three times weekly at 25 °C showed better seedling growth. In an in vitro experiment, seedlings germinated in distilled water and one-tenth strength Murashige and Skoog medium had superior shoot induction competence compared with the other germination media. The cytokinins meta-Topolin (mT) and meta-Topolin riboside (mTR) at 5 μm gave significantly higher shoot multiplication rates compared with the control and benzyladenine (BA)-treated plants. A higher abnormality index was recorded for BA-treated plants. The findings of this study will be beneficial for commercial propagation of Aloe ferox.

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Georgina D. Arthur, Adeyemi O. Aremu, Manoj G. Kulkarni and Johannes Van Staden

As a result of the growing concerns about the adverse effect of chemicals on the environment, agricultural practices involving organic and environmental-friendly compounds are gaining acceptance globally. Tomatoes remain one of the most popular and widely grown vegetable crops. However, their growth requires a high supplement of nitrogen–phosphorus–potassium (NPK) fertilizer. The effectiveness of vermicompost leachate (VCL) as a potential replacement for the three elements (N, P, and K) during the growth of greenhouse tomatoes was evaluated. Morphological appearance of the tomato seedlings was remarkably enhanced when Hoagland’s nutrient solution (50%) was supplemented with VCL (1:10 v/v). In the absence of both P and K, the addition of VCL significantly (P = 0.05) increased various growth parameters such as shoot length, leaf number as well as shoot and root fresh weight compared with the control tomato seedlings. The detrimental effect of N deficiency on the growth of tomato seedlings was not alleviated with the addition of VCL to the nutrient solution. The photosynthetic pigment content in P-deficient and VCL-supplemented tomato seedlings was significantly higher than the untreated control. The presence of VCL alleviated the detrimental effects caused by deficiency of P and K during the growth of the tomato seedlings. Overall, the use of VCL was beneficial with either complete nutrient solution or in the absence of P and K. Findings of this study suggest that VCL could serve as a potential substitute for P and K deficiency.

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Mack Moyo, Manoj G. Kulkarni, Jeffrey F. Finnie and Johannes Van Staden

Marula [Sclerocarya birrea (A. Rich.) Hochst. subsp. caffra (Sond.) Kokwaro (Anacardiaceae)] is used in many African countries as a food crop and is also in demand for industrial purposes. The fruit pulp has high vitamin C levels and the nuts have a high protein and oil content. The fruit pulp is commercially used in the production of an alcoholic beverage (Amarula Cream) and the oil is gaining importance in the cosmetic industry. Although attempts are being made to domesticate this high-value indigenous tree, there is very limited information available on aspects of seed germination. Our study investigated the role of light, temperature, cold stratification, and after-ripening on seed germination of S. birrea. Temperatures between 25 and 35 °C favored germination of opercula-removed seeds under continuous dark conditions. White light completely inhibited seed germination with the inhibitory effect being reversed when seeds were transferred to dark conditions. This photoinhibitory effect on opercula-removed seeds was lost after 12 months of seed storage at room temperature in the dark. Cold stratification (5 °C) of intact seeds for 14 days significantly improved germination (65%) as compared with nonstratified seeds (32%). Pregermination treatments (acid scarification, boiling water, dry heat, soaking, and plant growth regulators) of S. birrea seeds did not promote germination. Seeds of S. birrea can be considered orthodox because they tolerated desiccation without significant loss of viability. Both intact and opercula-removed seeds readily imbibe water suggesting physiological rather than physical dormancy. The highest germination percentage was recorded under constant dark conditions at 25 °C for opercula-removed seeds exposed to an after-ripening period of 12 months. This study indicates that after-ripening, light conditions, and cold stratification are critical factors for germination of S. birrea seeds.