EL CASTAÑO: BIOLOGÍA, FISIOLOGÍA, GENÉTICA
European chestnut, Castanea sativa Mill., is a tree species with a wide distribution and an important economic role in Europe. As this is a threatened species, mainly due to ink and blight diseases, research efforts are focused on selection of resistant trees, propagation and development of new resistant hybrids through conventional breeding programmes. However, new biotechnological tools are being applied to chestnut research, and of the recent advances on the biology, physiology and genetics of European chestnut will be summarized herein. Vegetative or clonal propagation is important to produce large amounts of selected trees, but also as an important tool in tree breeding programmes, as it has the advantage over the conventional techniques of capturing all the genetic superiority while not entailing any gene segregation. Chestnut is a difficult-to-root species, especially at the mature stage, but using recently developed in vitro tissue culture technologies, the large scale propagation of selected genotypes is now feasible. Both the anatomical events and the role of endogenous plant growth regulators have recently been studied by means of an in vitro experimental model, demonstrating the differential response of easy and difficult-to-root material of the same genotype. Using the same experimental model, a number of research groups are currently studying genes differentially expressed in these materials. Ecophysiological approaches are now under development for examining the chestnuts response to potential global warming. A Portuguese research group, under the leadership of Dr. Gomes-Laranjo, is studying the thermotolerance of C. sativa during the vegetative cycle, as well as the photosynthetic response of hybrid clones and C. sativa cultivars. The study allows the discrimination of clones/genotypes regarding the increase of temperature, and how this discrimination may be related to the potential response of chestnut to diseases. The first generation of ink disease-resistant hybrids (C. sativa × C. crenata) have been deployed during the last fifty years in several European countries, as a consequence of conventional breeding programmes. Large backcross breeding programmes have not been, and probably will not be, carried out in Europe to obtain disease-resistant but nearly pure European chestnut trees, as is the case in USA with American chestnut. This in turn may have lead to the loss of specific characteristics of C. sativa. Supported by efficient regeneration in vitro systems through somatic embryogenesis, genetic transformation procedures have recently been developed for both European and American chestnut. Now that Agrobacterium-mediated transformation systems are in place, the time required to transfer a new set of genes into chestnut somatic cell lines and regenerate acclimatized somatic seedlings ready for ink/blight screening could be as little as two years. The chestnut population in Europe is highly complex due to its different expansion areas, selection of varieties, depletion due to diseases, cultural abandonment, use of pure Asian species, and the spread of first-generation Euro-Asian hybrids resistant or tolerant to diseases. Many researchers in Europe are currently focusing their efforts on verifying the genetic variability of C. sativa in both natural populations and cultivated varieties, which will be of great relevance for the study and the conservation of biodiversity and adaptative potential. For these purposes, molecular markers are being used, which will help in the understanding of both short- and long-term evolution, in the studies of migratory routes, and in adaptative traits, such as phenology, juvenile growth and carbon isotope discrimination. The identification of quantitative trait loci (QTLs) will be an important tool for developing early selection methods. The general use of molecular markers will benefit both the research progress and the productive sector.
Ballester, A. (2008). EL CASTAÑO: BIOLOGÍA, FISIOLOGÍA, GENÉTICA. Acta Hortic. 784, 79-82