• Describe the role of grafting in human history. • Distinguish between the use of seedling and clonal rootstocks. • Describe how natural grafting can affect tree performance. • Describe how the rootstock and scion heal together during grafting. • Define how specific genetic, environmental, and management factors and polarity affect graft success. • Determine what kinds of plants can be grafted. • Define graft incompatibility— its symptoms, causes, and control. • Describe important ways the rootstock (root system) influences the scion (shoot system) and vice versa. 11 Principles of Grafting and Budding

A History of Grafting

The effects of cocultivation with Agrobacterium tumefaciens, regeneration and selection conditions on the transformation efficiency of citrange (Citrus sinensis L. Osbeck×Poncirus trifoliata L. Raf.) have been investigated. Factors such as cocultivation period, preculture of explants, use of acetosyringone or feeder plates during cocultivation, cocultivation on a medium rich in auxins, postcultivation in darkness, and different kanamycin concentrations for selection were assessed. A 3-day cocultivation on a medium rich in auxins improved transformation frequencies, since it increased the number of dividing cells competent for transformation, at the cut ends of the explants. Exposure of explants to darkness for 4 weeks on selection medium resulted in further callus development and increased the regeneration frequency of transgenic shoots. Furthermore, this treatment drastically reduced the number of regenerated escape shoots. A transformation efficiency of 41.3% was achieved using the optimized transformation procedure.

Agrobacterium-mediated transformation of citrange: factors affecting transformation and regeneration

High efficiency Agrobacterium-mediated transformation and regeneration of citrus

Publisher Summary This chapter discusses various closteroviruses Closteroviruses not only share similarities in particle morphology and biochemistry, but several members of the group seem to have common biological properties such as semipersistent mode of transmission by their aphid vectors and induce similar ultrastructural changes in their respective hosts Members of this group have a moderate host range, but some of them cause extremely important economic diseases Of the 10 typical closteroviruses, six are described, and purification methods for three are presented that enabled their partial characterization With certain similar sized viruses such as beet yellow virus (BYV), carnation necrotic fleck virus (CNFV), and probably beet yellow stunt virus (BYSV), cytopathology, serology, and amino acid composition indicate close relationships, with a variation nearing that assumed among different strains of some other elongated plant viruses The RNAs of BYV and CNFV are about twice the size of chlorotic leaf spot virus (CLSV) and heracleum latent virus (HLV), and it is possible to visualize the origin of the heavier genomes via dimerization of the half-size units Infectivity is associated with normal sized BYV particles and centrifugation of formaldehyde-treated RNAs indicated that the heavy sized RNAs are intact and resist treatment believed to dissociate noncovalent links among segments of RNA

The Closteroviruses: A Distinct Group of Elongated Plant Viruses

Micropropagation of Woody Plants

Improvement of shoot-tip grafting in vitro for virus-free citrus.

Murashige et al. (1972) developed a technique for grafting the small apical shoot of citrus to the top of a decapitated seedling grown in vitro. A few of these grafted plants, when indexed, were found freed of exocortis and stubborn pathogens. Also, Temple tangors derived by shoot-tip grafting in vitro (STG) were relatively thornless, flowered and fruited early, and appeared identical to the parent plants. Navarro, Roistacher, and Murashige (1975) improved the technique by testing various media formulas, different ways of placing the scion tip on the decapitated epicotyl, different rootstocks, light intensities, and different sources and sizes of the scion shoot-tip on graft success. Suc-

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Recovery of Citrus Selections Free of Several Viruses, Exocortis Viroid, and Spiroplasma citri by Shoot-Tip Grafting in vitro

Virus and viruslike diseases are the most serious threats facing the Spanish citrus industry today. Tristeza in 1972 affected 82,000 hectares of citrus (Guardiola, 1974), and is now the most dangerous citrus disease in Spain. Because of tristeza, sour orange can no longer be recommended as a rootstock and such tristeza tolerant stocks as citranges and Cleopatra mandarin are being substituted. However, since nearly all trees in Spain may have exocortis (Planes et al., 1968) the use of citranges may lead to another serious problem because of their susceptibility to exocortis. Xyloporosis (cachexia) is widely distributed in Spain (Planes et al., 1973) and its presence may diminish the effectiveness of Cleopatra mandarin as a rootstock. Psorosis and psorosis-related viruses are present in much of our citrus and presumably add to decline and stunting of trees, thereby increasing economic loss. Similarly, impietratura is present in several varieties and is an important factor in diminishing

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The Citrus Variety Improvement Program in Spain

/pdf/effect-of-size-and-source-of-shoot-tips-on-psorosis-a-and-2z2vxh67xr.pdf

T. Murashige

Papers

Improvement of shoot-tip grafting in vitro for virus-free citrus.

Recovery of Citrus Selections Free of Several Viruses, Exocortis Viroid, and Spiroplasma citri by Shoot-Tip Grafting in vitro

The Citrus Variety Improvement Program in Spain

Effect of Size and Source of Shoot Tips on Psorosis-A and Exocortis Content of Navel Orange Plants Obtained by Shoot-Tip Grafting in vitro