Ngoc-Thang Vu

Growth, Physiology, and Abiotic Stress Response to Abscisic Acid in Tomato Seedlings

The effect of abscisic acid (ABA) on growth, abiotic stress tolerance, and physiology of tomato seedlings was investigated. To examine the effect of ABA concentration on growth and abiotic stresses, six ABA concentrations (0, 10, 50, 100, 150, or 200 mg·L-1) were applied by foliar spraying once a day for 10 days. The effect of ABA application number was also studied by using different timing at one ABA concentration (100 mg·L-1) once a day for 1, 3, 5, 7, and 9 days. The effect of ABA on physiology of tomato seedlings was examined by using two concentrations (50 and 100 mg·L-1) as compared to the control (non-ABA). Foliar application of ABA decreased the growth characteristics of tomato seedlings in a concentration-dependent manner; however, no statically significant difference was observed between the 50 and 100 mg·L-1 treatments. Furthermore, although growth parameters decreased statistically with increasing number of ABA treatments, there was no difference between the 3 and 5 application treatments. Application of ABA enhanced stress tolerance (cold and drought) of tomato seedlings by delaying the starting time of wilting point in drought conditions and reducing the relative ion leakage and chilling injury index in low temperature in all treatments. The transpiration rate decreased significantly, while stomatal diffusive resistance increased significantly with increasing ABA concentration. The relative water content decreased significantly during the period without irrigation. However, relative water content increased with increasing ABA concentration. The ABA enhanced drought tolerance of tomato seedlings by delaying the start time of wilting point from day 3 in the control to day 5 and 7 in the 50 and 100 mg·L-1 treatments, respectively. Integrating this result data, we can determine the ABA’s ability to maintain of seedling quality at low temperature and water deficit condition.

Enhanced Graft-take Ratio and Quality of Grafted Tomato Seedlings by Controlling Temperature and Humidity Conditions

This study was conducted to enhance graft-take ratio and quality of grafted tomato seedlings by controlling temperature and humidity during the healing and acclimatization processes. Three temperature levels (20℃, 23℃, and 26℃) were carried out to determine optimum temperature on four rootstocks. In addition, twelve combinations of three relative humidity levels (70%, 80%, and 90%) and four temperature levels (17℃, 20℃, 23℃, and 26℃) were set up to evaluate the effect of relative humidity and temperature on the graft-take ratio of grafted seedlings. In the other hand, five relative humidity periods (H0, H1, H2, H3, and H4: 90% relative humidity for first 0, 1, 2, 3 and 10 days and afterwards relative humidity was reduced to 70%, respectively) were examined effect of relative humidity periods on the graft-take and quality of grafted seedlings. The higher graft-take ratios (84.0~87.4%) were showed at 23℃ compared to 20℃ and 26℃ in all rootstocks. Graft-take ratios decreased and number of diseased plants increased at high temperature. The graft-take ratios increased with increasing relative humidity in all temperature levels on the 3 rd and 7 th day after grafting. However, increasing relative humidity significantly increased percent of diseased plants. The graft-take ratio reduced at (26℃) and (17℃) temperature under all relative humidity conditions. The graft-take ratio increased with increasing period of 90% relative humidity. Maximum graft-take ratios were observed in H2 and H3 treatments. Graft-take ratio decreased with increasing 90% relative humidity for 10 days (H4). Diseased plants had not been found in H0, H1, H2, and H3 treatments. Seedling quality was improved through increasing fresh and dry weight of root, compactness, and root morphology of tomato seedlings in H2 and H3 treatments. Therefore, high relative humidity (90%) for first 2 or 3 days and afterwards reduced low relative humidity (70%) at 23℃ condition during healing and acclimatization promoted the graft-take and quality of grafted tomato seedlings.

Effect of Red LEDs during Healing and Acclimatization Process on the Survival Rate and Quality of Grafted Tomato Seedlings

This study was designed to determine the effect of red LEDs during healing and acclimatization process on the survival rate and quality of grafted tomato seedlings. Red LEDs and no light (darkness) were used for treating three rootstock cultivars, which are ‘B-Blocking’, ‘Kanbarune’, ‘High-power’ in healing room. Results showed that survival rates of grafted seedlings in red LEDs were higher than those in no light treatment. Significant variation on survival rates of rootstock cultivars was observed in no light treatment but there was not significant variation in red LEDs treatment. Light treatment also reduced the percentage of infected plants, except for the ‘Kanbarune’ cultivar. Seedling quality in red LEDs was better than that in no light treatment by improving growth parameters such as plant height, leaf length, leaf width, leaf area, fresh and dry weight of shoot and root. Light treatments and rootstock cultivars did not affect number of leaves, leaf chlorophyll value and T/R ratio of seedlings, but seedlings in red LEDs were significantly more compact than those in no light treatment. Moreover, the root morphology of seedlings such as total root surface area, total root length, and number of toot tips in red LEDs was also greater than that in no light treatment.

Influence of Short-term Irradiation during Pre- and Post-grafting Period on the Graft-take Ratio and Quality of Tomato Seedlings

The objective of this study was to evaluate influence of short-term irradiation during pre- and post-grafting period on the graft-take ratio and quality of tomato seedlings. Irradiation by six light qualities, darkness, white fluorescent lamps (WFL), red LED, far-red LED, blue LED, and natural light, were used to treat seedlings for 10 days before grafting. And Irradiation by five light qualities, darkness, WFL, red LED, far-red LED, and blue LED, were used to treat seedlings for 10 days after grafting, during healing and acclimatization periods. When short-term irradiation was applied before grafting, the graft-take ratios (27.8–66.7%) were considerably low in all light treatments as compared with natural light (96.7%). The graft-take ratio of red LED was not statically different with WFL treatment, but higher than far-red and blue LED treatments. The lowest graft-take ratio (27.8%) was observed in darkness treatment. Changing light intensity before grafting was the cause of reduced graft-take ratios in this study. There was no significant difference among natural light, WFL, and red LED treatments in growth parameters, except for leaf chlorophyll level, leaf width, and fresh weight of root, but decreased in seedlings treated with far-red LED, blue LED, and darkness. Graft-take ratios (68.5–100.0%) were enhanced when short-term irradiation was applied after grafting. The maximum (100%) graft-take ratio was recorded in red LED treatment, but was not statistically different with the WFL treatment. The lowest graft-take ratio was also observed in the darkness treatment. Plant growth responses to red LED were also similar with those to WFL after grafting. However, when short-term irradiation was applied after grafting, the lowest values of plant growth were observed in far-red LED treatment. The plant growth parameters were similar in seedlings treated with darkness and blue LED, but lower than red LED and WFL treatments. The root morphology was improved in seedlings treated with red LED after grafting by increasing total root surface, total root length, and number of toot tips. Seedling quality increased at 35 days after transplanting in the red LED treatment by increased plant growth parameters, especially compactness and root morphology, as compared with other treatments.

Effect of Water Content in the Substrate of the Scion and Rootstock during Pre- and Post-Grafting Period on the Survival Rate and Quality of Tomato Plug Seedlings

This study evaluated the effect of water content in the substrate during pre- and post-grafting period on the survival rate and quality of tomato plug seedlings. Nine combinations of three water levels (high, medium, and low) were set up in the substrate of both scion and rootstock. The water content in the substrate of the scion did not affect the survival rate of grafted tomato seedlings, while the survival rate was statically different among the various water contents in the substrate of the rootstock. The maximum survival rates (100%) were observed in seedlings treated with high water levels in the substrate of the rootstock, and the survival rates declined with decreasing water content in the rootstock substrate. The growth characteristics were not significantly affected by different water content in the scion substrate, while they were statically different among the seedlings treated with various water contents in the rootstock substrate. The growth characteristics decreased with decreasing water content in the rootstock substrate. The highest value of compactness was observed in grafted seedlings, which combined medium water level in the scion and high water level in the rootstock substrate treatment. The root morphology of tomato seedlings was also affected by water content in the rootstock substrate. The total root surface area, total root length, and number of root tips decreased with deceasing water content in the rootstock substrate.