Báo cáo khoa học: "breeding strategy for cork quality"

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Note breeding strategy for cork quality Quercus suber L M MI Roldão d’Alpuim, Florestal Nacional, R do 1300 Lisbon, Estação Borja n°2, Portugal Summary — According to official statistics, cork oak (Quercus suber L) occupies about 670 000 ha, mainly distributed to the south of the Tagus River. This represents about 22% of the country’s forest area, 8% of its total area and produces about 52% of the total cork production which amounts to 307 500 tonnes. In face of its importance, and to avoid a decrease in the area of the species and the quality of cork, it is urgent to introduce effective silvicultural and breeding techniques. The aims of this paper are to analyze the breeding programs for cork oak in which the Forest Research Station (EFN) is involved which are concerned with mass selection, vegetative propagation and progeny tests. These breeding programs must be very specific because of the characteristics of cork oak. Quercus suber / cork quality / breeding strategy / vegetative propagation Résumé — Stratégie d’amélioration génétique de Quercus suber L. D’après les statistiques offi- cielles, le chêne liège (Quercus suber L) occupe une surface approximative de 670 000 ha au Portu- gal. Son aire, principalement répandue au sud du Tage, représente 8% de la superficie totale du pays et 22% de la surface forestière. La production du Portugal représente 52% de la production mondiale soit 307 500 tonnes par an. Compte tenu de l’importance économique de l’espèce et des risques de réduction de la quantité et de la qualité du liège produit, il est devenu urgent de dévelop- per des techniques sylvicoles efficaces et de mettre en place un programme d’amélioration généti- que. L’objectif de cet article est de décrire le programme d’amélioration mené par l’EFN (station de recherches forestières). Il préconise la sélection massale, la multiplication végétative et la mise en place de tests de descendances. Le programme d’amélioration doit prendre en compte les particula- rités du chêne liège. Quercus suber / qualité du liège / stratégie d’amélioration / multiplication végétative INTRODUCTION volucre of the stem and branches, and the speed of its regeneration whenever cork is removed. The physical, mechanical and Cork oak (Quercus suber L) is an ex- chemical characteristics of cork make Q tremely variable Mediterranean species, of suber an economically very important spe- which several varieties have been recog- cies (Natividade JV, 1950; Gois E, 1992). nized. The characteristics which distin- guish this species from all other oaks are is the world’s most important Portugal the thickness attained by the suberous in- both for quality and producing country
quantity but production is not sufficient to of cork, as evidenced by several peeling opera- tions, will be the main criterion. Plus trees will fulfill global market demands (Anonymous, constitute the reproductive population which will 1990a). Some first class quality cork is be the basis of the whole breeding program. therefore imported representing approxi- These trees, once selected, will be represented mately 7% of the raw material used. in clone bancks and will provide the material for In the face of the increasing needs for propagation. cork of high quality and a tendency for clonal and progeny tests will Simultaneously, yields to decrease, it is urgent to introduce be established under different ecological condi- tions. These will allow the investigation of, for ex- proper silviculture as well as improvement ample, intraclonal and interclonal variability as by breeding. well as the genotype-environment interactions. The Forest Research Station (EFN) has Half-sib progeny tests will provide information developed a research strategy aimed at the reproductive capacity of the various plus on improving cork oak. It is intended to deter- trees and their general combining capacity. mine the heritabilities of various character- Considering the complex floral biology, the istics under study, possible genetic gains, immediate accomplishment of large scale con- and simultaneously to achieve an immedi- trolled pollination trials will be difficult. Due to ate improvement by the utilization of seeds the lack of knowledge about heritability of cork quality, a fundamental aspect, it was decided to or propagules from trees selected on the carry out a short preliminary test involving con- basis of cork quality. trolled crosses using 5-6 trees each of good and poor quality. Some other aspects will also be studied: the MATERIALS AND METHODS relationship between the rate of growth and cork quality, the influence of environment on quality of cork and a search for any relationships be- Presently EFN is carrying out a cork oak breed- tween quality and any morphological character- ing program aimed at the replacement of old istics. Carvalho (1991) recommended that a de- and decrepit cork oak stands as well as estab- tailed study of the periderm be carried out. lishing new areas on marginal or uncultivated agriculture land. It is intended to use the vari- ability existing within the stands to concentrate the genes responsible for the best qualitative RESULTS AND DISCUSSION characteristics of cork in some individuals. Mass propagation of these trees will allow an increase of production and improvement of quality. Projects which have already been started planned are described below. Selec- It should be noted that cork oaks are char- or are acterized by a very high allogamy, great genet- tion of plus trees on the basis of the quality ic variability, late flowering and slow develop- of cork: 230 selected trees have already ment of ultimate quality of cork (Roldão, 1986). been registered in the principal cork oak The harvest of virgin cork takes place at age producing areas in the country. They were 25-30, and, thereafter, every 9 years. At the selected mainly on the basis of the quality harvest in the 43-48th year, cork is considered of cork produced, but other parameters to be of the average quality produced over the rest of the economic cork production period of taken into consideration, such were as the trees, up to age 100-120 years. So, the stem straightness and branch angle, resis- strategy for breeding this species must take tance to insects and diseases, and the these characteristics into account. The pro- straightness of the in the cork (Car- grain posed model for improvement is depicted in valho, 1991).Cork quality was determined figure 1. from studies of structural aspects of the in- From the base population, some plus trees ner side (ventre), the mass and (massa), will be selected. The use of rigorous and sound the external side (costas). criteria in selection will be essential. The quality
year-old stocks. Top grafting has frequent- Vegative macropropagation: vegetative ly been found to suffer from rejection of the propagation is not easy to accomplish with graft unions (Roldão et al, 1990). cork oak, either through grafting or cuttings, although some success has been Correia (1981) used bud grafting to es- achieved. This approach includes the use tablish a small single clone plot but this of homoplastic and heteroplastic bark method requires very skilled workers. This grafting in cork oak and holm oak (Quer- plot, now aged 14-15 years, has not pro- cus rotunfifolia Lam) with 4-5-year-old duced seeds so far, leading to the belief stocks and also through side grafting in 2- that the technique may be valuable for re-
material from old trees. juvenating REFERENCES Experi- being carried ments are out to test this hy- pothesis. Inventário florestal do so- Anonymous (1990a) breiro. Divisão de Inventário Florestal, Estu- The production of rooted cuttings from dos e Informação 300, Lisbon young plants, under controlled environ- Anonymous (1990b) EEC Program: Competi- mental conditions, has been successful tiveness of and Management of Agriculture (Roldão, 1990). The strategy outlined for Agriculture Resources. Project Improvement the cork oak breeding program at EFN of quality and productivity of cork oak ecosys- consists of obtaining vegetative reproduc- tem tion of the plus trees by means of bud and Perfil florestal. Direcção Ger- Anonymous (1991) side grafting and later mass propagation al das Florestas. Divisão de Estudos. by cuttings. provisória). Abril, Lisbon (Versão Establishment of clone banks: the clone Carvalho A zonagem de (1991) Classificação e qualidade das cortiças Protuguesas. Inven- bank of plus trees selected has been start- tariação dos sobreiros produtores de cortiça ed. de superior qualidade. Final report 1988- Investigation of morphological and struc- 1990. Project PIDDAC 002, Lisbon tural correlations: a forecast of the quality of Correia C (1981) Aspectos suberícolas. A Inves- cork is very important for a breeding pro- tigação ao serviço de uma agricultura reno- gram. vada. Bol Inst Prod Flor 511, 112-118 Gois E (1992) A Floresta Assuming that the cork oak trees pro- Portuguesa. Portucel, Lisbon duce cork of high quality and show a conti- nuity of consecutive (renewed) periderms Natividade JV (1950) Subericultura. Direcção Geral dos Serviços Florestais e Aquícolas, as opposed to the peridermic rings which Lisbon characterize the other Querciniae, as well Nóbrega F, Rodo J, Sousa JR (1990) Identifi- as the products resulting from hybridiza- cação de isoenzimas em polén de sobreiro. II tion with Quercus suber, we intend to pur- Congresso Florestal Nacional, Porto, Facul- sue the study of their periderms from the tade de Economia. Novembro de 1990, 13 p 3rd year of sowing (Carvalho, 1991).This Roldão I (1986) Perspectivas para o melhora- is a very relevant point to be considered in mento florestal da espécie Quercus suber L. experiments with young plants. I Congresso Florestal Nacional, Lisboa, 117- 119 At the same time, high quality clones are being characterized using chemical Roldão I (1990) Macropropagação vegetativa do sobreiro. II Congresso Forestal Nacional. methods, looking for eventual genetic cor- Porto, Facultade de Economia. Novembro de relations between the occurrence of cer- 1990 (in press) tain isoenzymes, the characteristics of the Roldão I, Alpuim M, Bohm J (1992) Conside- cork tissue and the environment. A study rações sobre os resultados já obtidos na of the isoenzymes and proteins in pollen propagação vegetativa do sobreiro, esta- produced by cork oak has been started us- caria e enxertia. CEE Symposium on cork bi- ing electrophoresis acrylamide gel (No- on ology, Lisboa, 10-11 December 1990. Sci brega et al, 1990). Gerundensis 18, 85-89