Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 5.27

Gene flow in wild population of Lactuca serriola analyzed by SSR markers

M. VISCHI, I. SCOTTI, E. VALENT, S. DELLACASA, A.M. OLIVIERI

Dipartimento di Produzione Vegetale e Tecnologie Agrarie, Via delle Scienze 208, 33100 Udine, Italy

lettuce, gene flow, SSR markers, introgression

This study was carried out in the frame of the EU project ANGEL (Analysis of gene flow from crop to wild forms in letture and chicory and its population-ecological consequences in the context of GM-crop biosafety). Lactuca serriola is closely related to cultivated lettuce and was selected as a model system to establish the degree of outcrossing under field circumstances taking in account its adaptation to a wide range of environmental conditions and the high degree of invasiveness.

Five wild lettuce populations were identified in the North Est of Italy and in Switzerland around Fribourg. About 50 plants for each population (or, where possible, the whole population) were sampled, and their position recorded. A molecular fingerprint of each plant was obtained using 11 SSR markers developed in L. sativa. Allele frequencies were calculated for each locus and each population. The number of alleles per locus was between 3 and 11. The level of heterozygosity was generally low but was higher in populations growing in more central locations relative to the species range (S. Dorligo, Italy). High level of genetic similarity was detected between population except for one population (Amaro, Italy) growing in conditions of spatial isolation.

No linkage disequilibrium was detected both for single populations and for the 5 populations considered as a whole, suggesting levels of recombination high enough to prevent disequilibrium to take place.

Gene flow between population was calculated according to the private allele method and by calculation of F_st value. Both methods revealed an absent or very low gene flow with the only exception of two Italian populations (Mossano, Pozzuolo). Combining the molecular profile of plants with their position on the field, it was possible to analyze genotype distribution and heterozygote interspersion. By analysing spatial autocorrelation of genotypes, seed dispersion range was tentatively estimated to be effective up to 5 m. The limit of seed dispersion was estimated at 20 m, since genotypes were randomly distributed over this distance.

This could be used as a guideline for establishing safety distance in case of transgenic cultures being grown together with natural relatives. Further analysis is nevertheless needed to better define population structure and to directly assess outcrossing level in this species.