DISTRIBUTION OF WALNUT
The walnut (Juglans regia L.) is a species native of the mountains of Central Asia that grows scattered as minority component of mixed deciduous forests from southern Europe to India. It lies in the Balkans (Hungary, the former Yugoslavia, Bulgaria, Albania), in the Caucasus, in Asia Minor (Turkey, northern Iraq and Iran), Central Asia (the northern boundary in Kirguistán) and has its eastern boundary in the north of India. In Western Europe, the distribution is mainly concentrated in human settlements, roads and crops. In Spain it is dispersed across the surface forming very small populations.
DISTRIBUTION OF WALNUT IN SPAIN (THIRD NATIONAL FOREST INVENTORY)
It is a species of long-term that grows in a wide variety of substrates, mainly in fresh soil, very rich and loose. It has problems to regenerate naturally, mainly due to the presence of animals that eat its fruit. It prefers warm and warm-hot climates because the late frosts are a major limiting factor that affects flowering and the development of its shoots. Under these conditions, altitude is not a limiting factor and it can be found from low elevations up to 2500 meters.
Its economic interest is in its dual aptitude. On the one hand, the production of fruit, prized for human consumption. In the other hand, the production of one of the most prized woods in Europe because of its features and its easy machining. This fact influenced in increasing the area of distribution of the species.
In 1997 began the breeding program of walnut in Galicia with the exploration and selection of 43 superior trees in Galicia. The material collected from the 43 trees was planted in 1998 in an trial of progenies in ‘Lourizán’ (‘Pontevedra’) and ‘Nullán’ (‘Lugo’). The last one was transplanted in the year 2000 in ‘Baralla’ e ‘Becerreá’ (‘Lugo’). In 1998 we collected material from 24 superior trees from the 43 in Galicia, 19 in ‘Asturias’ and 12 in ‘León’, establishing in 2001 the corresponding progenies trial in ‘Rebordelo’ (‘Pontevedra’) and ‘Daneiro’ (‘A Coruña’), although at the present only exists the Danero one. We also grafted spikes of trees, selected in a germplasm bank in ‘Lourizán’, which currently does not exist.
ORIGIN OF PLUS TREES AND TESTING PROGENIES
The studies have mainly focused on characters related to wood production, finding significant differences between progenies for the characters of growth, phenology, damage by frost, number of apical branches or damage by Phytophthora cinnamomi, but not for the characters of wood shape or apical dominance. Families with earlier budding presented further damage by late frosts and, therefore, greater number of apical branches. Moreover, with the selection of the best progenies within families, we obtain higher profits that with the selection of progenies.
We also carried out studies with RAPDs molecular markers of 56 clones obtained in the germplasm bank, with the objectives to identify the material and establish genetic relationships. We identified 49 groups of clones and we determined the absence of geographic structure in the genetic variability of the studied clones. Further studies with isozymes, allowed us to demonstrate the conservation of the variability of the population of improvement, over the naturalized populations of its geographical area.
The provenance-progenies trials consists of four original populations of four sites in northern Spain, distinct from the climate point of view. The trial was initially established in 2001 in two nurseries: one in ‘Nullán’ (‘Lugo’) and another in ‘Mas Valero’ (‘Castellón’), and in the year 2005, the material of ‘Nullán’ was established in field in ‘O Pino’ (A Coruña).
ORIGIN OF SPANISH POPULATIONS AND PROVENANCE-PROGENIES TRIALS
During the first three years, we carried out the measurement of characters of growth, phenology, form and survival. Studies have determined significant differences between populations for the characters of growth and phenology, being the variability of these characters populations greater between populations than between families. These results should be considered in the conservation and improvement of walnut in Spain. Also, we detected significant differences between the two sites, so it is recommended more comprehensive studies to make recommendations of use.
(C-jr-3) Díaz, R., Fernández-López, J. (2001a) Prospección y selección en campo de árboles superiores de Juglans regia L. en el noroeste de España. 3º Congreso Forestal Español. 25-28 de Septiembre, Granada
(C-jr-2) Díaz, R., Fernández-López, J. (2001b) Evaluación de un ensayo de progenie de Juglans regia L. en Galicia. 3º Congreso Forestal Español, 25-28 de Septiembre, Granada
(C-jr-4) Díaz, R., Abuín, C., Fernández-López, J. (2002) Comparison of isozyme and RAPD markers for revealing genetic variation in walnut species (Juglans regia L.). International Conference DYGEN on Dynamics and Conservation of Genetic Diversity in Forest Ecosystems. 02-05 de Diciembre, Strasbourg, Francia
(R-jr-2) Abuín, M., Díaz, R., Fernández-López, J. (2002) Identification of Juglans regia L. genotypes using RAPDs molecular markers. Forest Genetics 9(1):31-37
(R-jr-4) Alfonsín, J.; Abuín, M.; Díaz, R.; Fernández-López, J. (2004) Caracterización de la variabilidad genética de una población de mejora de Juglans regia L. Investigación Agraria: Sistemas y Recursos Forestales 13(3):518-526
(R-jr-5) Díaz, R.; Fernández-López, J. (2005) Genetic variation at early ages for several traits of interest for timber-production breeding of Juglans regia. Canadian Journal of Forest Research 35:235-243
(R-jr-7) Díaz, R., Baoune, N., Ninot, A., Fernández-López¸ J., Aletà N. (2006) Performance Differences and Genetic Parameters of Four Local Spanish Populations of Juglans regia in the North of Spain. Acta Horticulturae 705:103-108