Báo cáo khoa học: "Grafting of oaks with variegated"

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Original article Grafting of oaks with variegated leaves Z Borzan Faculty of Forestry, Department of Forest Genetics and Dendrology, 41001 Zagreb, PO Box 178, Croatia Summary — Among 1-year Quercus robur L seedlings, several plants were selected, differing from others in the population by their variegated leaves. Such plants could be useful in arboriculture, if we could fix the appearance of variegated leaves and solve the problems of vegetative propagation. This paper discusses the cytoplasmic inheritance of oak leaf variegation and describes the methods of grafting. Grafting and callusing of grafts in a mixture of sawdust and moss enables the production of an average of 32% firmly joined grafts at the end of the first growing season. Quercus robur L / leaf variegation / vegetative propagation Greffage de chênes aux feuilles bigarrées. Plusieurs plants d’un an de Quercus robur Résumé — L présentant des feuilles bigarrées ont été sélectionnés. Ces plants pourraient être utilisés en horti- culture, si les problèmes de fixation du caractère bigarré et de multiplication végétative sont résolus. Cet article discute de l’hérédité cytoplasmique du caractère bigarré et présente une méthode de greffage. Le greffage et la cicatrisation de la greffe dans un mélange de sciure et de mousse per- mettent d’obtenir 32% de greffes fermement adhérentes aux porte-greffes à la fin de la première sai- de végétation. son Quercus robur L / feuilles bigarrées / multiplication végétative INTRODUCTION the device grafting method used by by Borzan and Littvay (1989). In addition to our own selected oaks, we have collected Among the pedunculate oak numerous variegated samples from the Kilmacurragh seedlings in nurseries, individual spec- our Institute in Ireland. This paper discusses imens with differently variegated leaves the foliar variegation of pedunculate oak noticeable. We have selected 50 are leaves based on the available literature genotypes since 1987, with the aims of and presents the results of their vegetative monitoring foliar changes throughout the season and propagating the best variants propagation.
MATERIALS AND METHODS course of the 2nd and 3rd year, some of them changed to green leaves, indicating a loss of variegation. The behavior of figurative patterns of foliar var- A small number of plants (5) showed iegation of 50 selected pedunculate oak seed- lings has been monitored in the nursery since the same type of variegation on all leaves 1987. both in the 2nd and 3rd year (fig 2a, b, c). Scions from 5 of our own oaks and 4 from Two of them had second-flush leaves with trees at the Kilmacurragh Institute in Ireland (ta- larger variegated surfaces (fig 2b, c), thus ble I) were kept in the refrigerator (+ 5 °C) and differing from those of the first flush. grafted. Grafting was carried out in March 1991, using a home made grafting device fixed to a ta- Most of the plants (20) remained varie- ble and powered manually. The device cut a in the second and subsequent years gated groove on the root-stock and a cog on the scion but with only occasional variegation of their in the shape of the Greek letter Ω (fig 1). Joined leaves. Some produced green leaves in root-stocks and scions were kept for 14 days in the first flush and variegated ones in the a box completely covered by a mixture of wet, second (fig 2d), while others did the oppo- fine and coarse sawdust (75%) and moss (25%) at a stable temperature of 27 °C and an air hu- site. Among the latter group, 1 plant pro- midity of 70-80%. After 14 days, the callused duced only white leaves in the first flush and flushed grafts were taken out, planted in and green in the second. Soon after the containers, put in the shade in a heated plastic appearance of green leaves on that plant, house and protected both from spring frosts and the white leaves fell, after becoming strong sunlight. The remaining grafts were re- brownish. turned for further callusing for another 7 days. RESULTS Among 50 selected 1-year-old seedlings withdifferently variegated leaves in the
is much easier to perform regular "omega" 5-year-old plants had a One of the cuts on thicker scions. The plants with strongly variegated side branch though no short and thin shoots gave poorer results. variegated leaves occurred on the main Some grafted genotypes that were expect- stem. The variegated branch also had a ed to have variegated leaves produced certain number of completely green only green leaves throughout the season. leaves. These results support our previous find- Generally, the spring types of variega- ings (Borzan and Littvay, 1989) when we attractive than the summer tion are more concluded that it was possible to graft pe- ones, showing brighter white and yellow dunculate oak successfully and to recom- colors. In summer, individual variegated mend device grafting as a simple and low- parts of the spring leaves dry, especially if cost method. the plants are exposed to the sun. TableI shows the results of grafting. Out of the 113 plants grafted on 27 March DISCUSSION 1991, 36 had developed normally by mid- August, ie, 32% were considered fairly successful. Variegation was defined by Schultz (1936) (quoted by Rieger et al, 1976) as "... the depended primarily Grafting success in- occurrence, within tissue, organ, upon the thickness of the scion, because it or one
tion and Hoffmannii, for which Henny dividual, of a mosaic phenotype with re- (1982) concluded that their foliar variega- spect to pigmentation... It is a widespread tion is under the control of a single domi- phenomenon caused by several (observed nant nuclear gene. This assumption can inferred) mechanisms: 1. Plastid varia- or only be proved after spontaneous or in- tion and the behavior of plastid variants in duced flowering of these variegated oak somatic divisions of plants; 2. Genic insta- bility and the recurrence of somatic muta- seedlings, when it is possible to perform tions; 3. Instability of the phenotypic ex- controlled crossing. pression of genes as a result of position Second, those with foliar variegations effect; 4. Genetically controlled stickiness produced at each flush (fig 2b, c), with the of chromosomes; 5. Somatic crossing- different leaves of the first flush having a over; 6. Somatic behavior of ring chromo- type of variegation than those of the sec- and dicentric chromosomes; 7. In- somes ond. fection". Stable variegations are most desirable, All of these causes of oak leaf variega- because of their beauty and promise for tions are probably present in our plants, tree improvement work. The slower growth except the last. Variegated oaks change of our specimens of this kind is, at the mo- rapidly up to the age of 3 years. Usually, ment, a disadvantage because at 5 years after the 3rd year, their variegated features they are still too small to be grafted. become increasingly stable, while the sort- Occasionally variegated oaks can also ing of mutated plastids is very intensive be divided into two groups. First, those during the first 3 years, resulting in some with green leaves on the first flush and var- plants eventually having only green iegated ones on the second, or vice versa. leaves. Variegation of this type is quite stable, ie, However, the heritable properties of the foliar variegation appears every year only plastids (the sum total of the extrachromo- on the first-flush leaves or only on the somal genetic information is defined as second flush leaves. The extent of the plastom, after Renner (1929, 1934) (cited variegation on branches varies. Thus, it is in Rieger et al, 1976) ie, their ability to mu- advisable to mark the branches with attrac- tate and to multiply are of importance for tive and extended leaf variegation during a the expression of variegation. Tilney- season and to use them as scions the fol- Bassett (1963) considers variegated plants to assure a greater quantity lowing spring, to be chimeras. plastids in grafted plants. of mutated We have observed 2 main kinds of fo- The nature of this type of variegation is liar variegations among selected peduncu- not clear at the moment. It is probably late oak seedlings. caused by nuclear gene-induced plastom mutation with increased variegation fre- variegations (fig 2a, b, c) which Stable quency only at a certain time during the probably controlled by nuclear most are season (ie, only in a certain tissue layer of genes, causing mutations of 2 kinds. First, cells), for variegation appears repeatedly those with variegated leaves, produced at at a particular time during the growing sea- each flush, having different shades of son, while during the rest of the season the green, yellow, cream or white or combina- plant flushes with only green leaves. tions of these colors evenly distributed Second, occasionally variegated oaks through the whole leaf (fig 2a). Such fea- have foliar variegation as sports. Var- tures resemble the foliar variegation of can iegation of this type could be lost. Such Dieffenbachia maculata cultivars Perfec-
REFERENCES plants have several features. At least during the first part of the season, variegated leaves have large, nicely colored yellow- &jadnr;, Littvay T (1989) Vegetativno razmnoz- Borzan cijepljenjem. green or white-green patterns which may hrasta luznjaka strojnim avanje Sumarski list 113, 557-566 appear every year and remain stable. Of- RJ (1982) Inheritance of foliar variega- ten, white or yellow leaf parts shrivel and Henny tion in two Dieffenbachia cultivars. J Hered burn in full sun. It is advisable to raise them 73, 384 in half shade. However, sports are interest- Rieger R, Michaelis A, Green MM (1976) Glos- ing for possible vegetative propagation. sary of Genetics and Cytogenetics, Classical oaks grow fast- Occasionally variegated and Molecular. Springer-Verlag, Berlin than those with stable variegated er RAE (1963) The structure of Tilney-Bassett peri- leaves. clinal chimeras. Heredity 18, 265-285