MOLECULAR POPULATION GENETICS AND DYNAMICS OF CHESTNUT (CASTANEA SATIVA) IN EUROPE: INFERENCES FOR GENE CONSERVATION AND TREE IMPROVEMENT

Eighty-two European chestnut populations, from Greece, Italy, France, Spain and the UK were studied using 73 ISSR and 16 isoenzyme loci in a total exceeding 2100 trees and 25000 genotypic designations. A multivariate analysis was used in order to detect locus interactions in space, not directly observable with averaging techniques such as genetic distances, after data vector transformation. Discussion elaborates on the major gene pools of chestnut in Europe and on the differences and similarities observed between different populations, regions, and countries. Within-stand population dynamics were investigated via a gene flow analysis of 15 populations from six sites (two from Spain, two from Italy and two from Greece) using 12 SSR and 26 isoenzyme loci, through paternity analysis and spatial analysis of genetic diversity patterns. Within each stand, 26-43 trees were genotyped and 7-9 selected mother trees provided the half-sib progenies (16-22 seeds per tree) analysed (about 58000 genotypic designations). Cryptic and outcoming gene flow appeared reasonably high for a predominantly outcrossing species (about 64%), ensuring a number of incoming migrants per generation large enough to counterbalance loss of diversity by inbreeding and drift, while selfing was very low (<4%). Mating probability dropped below 0.01 for distances larger than 2 km, and increased up to about 10% for distances closer than 300 meters, indicating that in the presence of some clustering of like-genotypes, a certain amount of inbreeding is expected. These findings have important implications in gene conservation, stand restoration, and fruit orchard establishment and management, as well as tree improvement.