65 Grafting Morphology and Physiology Text Pages: 415 432. Objectives: 1. Be able to describe and explain the terms used in grafting. 2. Be able to describe and summarize the reasons for grafting plants. 3. Be able to describe and explain the sequence of events involved in graft union formation. 4. Be able to describe and explain problems associated with grafting plants. 5. Be able to apply grafting principles to propagation situations. I. GRAFTING MORPHOLOGY AND PHYSIOLOGY A. Introduction B. Terms Used In Grafting 1. Grafting - is the art of joining two or more live pieces of plant tissue together so 2. Stock (also called rootstock or understock) - is the part of a grafted plant that receives a. The stock could be just b. Or the stock could be 3. Scion - is the a. Any plant part can be used, but b. Buds alone can also be
66 4. Budding - is a form of grafting in which 5. Interstock (also called intermediate stock or interstem) - is a piece of stem grafted between a. Use interstock for better growth characteristics b. Note: If an interstock is used, c. Example: 6. Cambium (vascular cambium) - is the meristematic tissue that divides to form a. Cambial tissue is very important since b. Cambial tissue is a 7. Callus - mass of parenchyma cells that 8. Plant responses to wounding: a. Do plants heal themselves? b. The answer is i. plants grow new cells when ii. plant parts grow together during C. Reasons For Grafting 1. Perpetuate plants/cultivars that can be reproduced only by
67 a. Example: b. Producing certain cultivars of shade trees: i. although cuttings from some species can be successfully rooted, the root system is ii. over-wintering softwood cuttings from some tree species is particularly 2. Obtain benefits from certain rootstocks: a. Rootstocks may provide more b. Rootstock may better tolerate c. Rootstock may provide a more desirable i. Malling 27 - dwarf apple rootstock ii. Malling 7a semi-dwarfing apple rootstock iii. Malling 25 - a vigorous apple rootstock d. Rootstock origin: e. Rootstocks developed from seedlings have certain qualities: i. usually lack ii. grow deep iii. have genetic variation, which
68 iv. variability is reduced by v. others - f. Clonal rootstocks are popular since: i. usually provide known ii. growth characteristics of the scion iii. clonal material may be iv. certain problems may v. others - 3. Obtain benefits from certain interstocks: a. Double working - use of an b. Avoid certain incompatibilities, c. Example: 4. Changing cultivars of established plants called a. Necessary in fruit or nut orchards when b. Cross-pollinating varieties or cultivars are added c. Potential problem with three-in-one trees:
69 5. Obtaining plants with special growth habits: a. Usually seen for weeping plants or b. If weeping plants only grow horizontally or c. Shrubs trained to grow on a single stem are d. Trees or shrubs that are grafted onto long stalks or trunks are 6. Repairing damaged trees a. Usually considered when a tree trunk is severely girdled due to i. certain grafting techniques are used to ii. inarching and bridge b. Repair sections of a tree 7. Other reasons to graft plants a. Hasten reproductive maturity of i. woody plants from seeds can take ii. putting a scion from a seedling on b. Hasten plant growth rate - i. some species of grafted trees grow more quickly than
70 ii. examples: c. Study virus problems and virus elimination - d. Study plant developmental and physiological processes - D. Problems Associated with Grafting 1. Graft incompatibility is a situation/problem when 2. Scion rooting - the graft union is planted too deep a. The rootstock roots decrease b. The effect of the rootstock c. Avoid the problem by planting 3. Suckering - the rootstock sends up shoots a. Often the rootstock is b. The rootstock puts more energy into c. Eventually the scion is overtaken, and i. the desired cultivar is lost ii. examples: d. Correct the problem by pruning suckers
71 i. prune as low as possible ii. some chemicals can be applied E. Forming the Graft Union 1. Forming a graft union is a process of a. A foreign piece of wood (the scion) is inserted into the b. In growing together, environmental conditions must be 2. First step - Line up vascular cambiums: a. Reason: A callus bridge is formed by i. the cambial regions should be in close proximity to ii. the closer the cambial alignment, the faster b. Environmental conditions must be favorable for cell growth i. temperature much be within a range for ii. humidity should be high, or the wound should be enclosed iii. disease organisms should be kept out of the wound 3. Second step - wounding response: A necrotic layer forms 4. Third step - callus formation: Both stock and scion produce
72 a. Having optimum environmental conditions for cell growth b. Since the callus tissue is fragile, the scion should be c. Intermingling and interlocking cells provide 5. Fourth step - cellular differentiation: Xylem differentiates, phloem differentiates, and then a. This step means a meristem capable of b. The new xylem and phloem formations are generation steps 6. Fifth step - production of secondary vascular tissues: The new cambium in callus bridge forms new a. This vascular connection enables water and b. New xylem should be formed before c. Scion buds appear d. Why? 7. T-bud grafts - form a union differently a. T-budding process b. Callus from the stock's newest or youngest xylem intermingles and interlocks with
73 c. Cambium of stock is in the tissue flaps d. Note: Most callus cells are formed by rootstock i. the callus bridge can take 2 to 3 weeks ii. a new cambium often takes 8. Chip bud unions - form more rapidly than a. Chip bud process: b. Reasons for quicker graft union formation: i. scion tissue and stock stems are matched ii. cambiums of stock and scions should line up F. Summary c:\plsc300\12notes-7.doc