Year: 2016
Type: article
Abstract: Seedling development is a period of dynamic change within the overall vegetable plant and crop development period.For example, leaf area, stem length, and above-ground biomass can increase several fold within 1-3 weeks of emergence, possibly signaling high rates of carbon fixation on a per gram fresh weight basis and prescribed patterns of primary growth.Still, while general patterns of seedling development are familiar and the influence of individual major environmental factors on it are well chronicled, a reliable, accessible, and highly repeatable approach to describe the efficiency with which seedlings convert growth factors into biomass and partition it is unavailable.We hypothesized that plant and environmental data could be integrated into a single "seedling vigor" value allowing for more direct and consistent comparisons of seedling growth within and across experiments.We tested this hypothesis in a greenhouse experiment involving the simultaneous tracking of seven parameters of seedling growth (aboveground biomass and growth pattern) in twenty-three commercial tomato varieties and four environmental variables through 18 d after seeding.A formula created for the test used the plant and environmental data in calculating seedling vigor values and the experiment was repeated twice over a four-month period in the spring.Minimum and maximum seedling vigor values differed 79-to 575-fold among cultivars in runs 1 and 2, respectively, although relative variety vigor values were generally consistent between runs.These results demonstrate: 1) that varieties iii differ in their primary growth capacities under identical growing conditions and 2) that calculations of vigor like the one demonstrated here can reliably differentiate these capacities and help standardize reports including them.Normal seedling development, perhaps especially root-shoot communication and root and shoot level (carbon) partitioning, is severely disrupted in the process of grafting.In fact, grafting requires two steps that are very likely to alter normal seedling developmental patterns and, possibly, subsequent vegetative and reproductive growth.The first stage of grafting is to prepare seedlings of at least two varieties to exacting specifications, a process that can be made more efficient and reliable by a greater understanding of factors influencing vigor, as described earlier.Later stages involve cutting and connecting portions of the two seedlings then facilitating the single plant's healing as a newly-made physical hybrid.Employing whole ungrafted seedlings as controls, experiments exposing newly-grafted plants to various temperature and light conditions during healing offer two benefits.First, they strengthen understanding of abiotic influences on whole seedling growth through roughly 40 days after seeding (an under-studied period).Second, comparing control and grafted-plant values, these experiments help determine when and to what extent grafted plants reach normal developmental milestones and vascular capacity.The latter outcome requires an appropriate protocol for assessing seedling/grafted plant vascular capacity, a focus of a portion of this program.Vegetable seedlings are fully or partially mechanically defoliated immediately before grafting and their stems are severed before being 'splinted' to provide stability during healing.Collectively, the process: a) nullifies investments seedlings made in leaf and root production before grafting; b) disrupts water relations, growth regulator balances, and other aspects of physiology; c) requires more or less immediate reestablishment of fully functional vascular connections between root and shoot, a prerequisite for further vegetative growth and, later, iv fruiting under potentially stressful conditions; and d) delays the readiness of grafted plants for use in commercial production relative to standard ungrafted plants, also causing grafted plants to be more costly to produce than ungrafted ones.Overall, newly-grafted plants are expected to require photosynthetically-derived energy to heal and resume growth.However, it is also reasonable to expect them to have a diminished photosynthetic capacity and, possibly, tolerance to even moderate light and temperature levels.Regardless, it is important to document light and temperature effects on healing and regrowth, especially using approaches uncommon in much of the horticultural literature.Therefore, a quantitative method to monitor healing was developed then used to test the effects of pre-and post-grafting light levels on healing.Dye movement used to visualize transgraft union, root to shoot water movement and stem elongation were used to track plant condition.Both were greater in newly-grafted plants exposed to extended periods of light versus dark soon after grafting.Follow-up studies including a total of ten temperature-light intensity combinations as treatments during the healing period were completed.Plants exposed to moderate to high light levels (i.e., 150-300 μmol/m 2 /s) of light and moderate temperatures achieved the largest aboveground dry weight and compactness.These results suggest that, in practice, the benefits of promoting photosynthesis beginning immediately after grafting exceed the benefits of protecting against potentially damaging effects of light exposure, provided moderate temperatures can be maintained.The data also call for follow-up experiments regarding, for example, the effects of wavelength, duration, and other components of irradiance on core aspects of healing and shortterm regrowth.Interest in grafted plants stems partly from the expectation that their root systems are better able to acquire nutrients and water, resist abiotic and biotic stresses, and display more vigor that the root systems of the scion cultivar.If true, the optimal cultural, nutrient, and irrigation v management plans of grafted and ungrafted plants and their responses to individual combinations of growing factors are likely to differ.In another experiment, grafted plants representing three rootstock-scion combinations (3 rootstock, 1 scion) and ungrafted plants of the same scion variety were grown in open field, conventionally-managed plots containing one of two fertilization treatments (pre-plant fertilization only, pre-plant fertilization with standard fertigation).The fertilization treatment-grafting interaction was not significant.Yield tended to be higher in plots containing grafted versus ungrafted plants, regardless of fertilization treatment.˚Brix was higher in fruits from ungrafted versus grafted plants, while trends in pH and titratable acidity were inconsistent.These results support the emerging hypothesis that grafted plants are more productive than ungrafted ones under a range of soil conditions but that fruit chemical characteristics may also be altered by grafting.
Author: Bizhen Hu
Institution: The Ohio State University
Language: English
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2735857498