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 - 5.33

MOLECULAR CHARACTERIZATION OF NATURAL POPULATIONS OF TUBER MELANOSPORUM THROUGH AFLP AND SSR MARKERS

C. RICCIONI, A. RUBINI, F. TOPINI, F. PAOLOCCI

CNR Istituto di Genetica Vegetale Sez. di Perugia, Via Madonna Alta 130, 06128 Perugia, Italy

truffle, SSR, AFLP, Tuber melanosporum

T.melanosporum is a symbiotic truffle species for which a strictly selfing reproductive mode and the lack of a genetic structure, at least in a survey of populations from the northernmost range of species distribution (France and North Italy), it has been reported (Bertault et al. 1998). Under this scenario, the organoleptic differences among truffles of different proveniences were accounted to environmental causes only.

In attempt to verify whether such a thesis sounds also when populations from all the different production sites are considered, we decided to collect samples from natural truffle grounds distributed all over Spain, France and Italy and analysed them by means of AFLP and SSR markers.

A total of 180 specimens were tested by 4 AFLP primer combinations which revealed a strong genetic homogeneity in T.melanosporum (16% of polymorphic traits). AMOVA analysis showed that, despite a high intrapopulation variability (76%), a significant percentage (24%) of species variability was partitioned among populations. The genetic distance among populations was measured by the Nei’s index (Nei, 1978) and the PCA (Principal Coordinate Analysis) showed that, although most of the populations are grouped in a strict area of the diagram, some of them (for instance Subasio and Cerreto, both from Umbria) are well split off. In sum, no significant correlation emerged between genetic and geographic pairwise distance values among the 19 T.melanosporum populations, however few of them could be typed for the presence of exclusive and/or more frequent than in other groups, AFLP bands.

The T.melanosporum genetic polimorphism was also assayed by STMS analyses. Three polymorphic and single-locus SSR loci (ME2, ME4 and ME7) were selected and screened over 80 ascocarps belonging to 8 populations from Italy, France and Spain. None of the individuals was found to be heterozygous at any of the loci. ME2 and ME4 were quite uniform showing only two allelic forms, but interestingly, one allele of the ME2 locus was present only in the Navarra population. On the other hand, the ME7 locus was more polymorphic and appeared in 11 allelic forms, two of them were exclusively present in two populations already typed by AFLPs (Capodacqua and Cerreto).

Both AFLP and SSR-based germplasm screenings confirmed a strictly selfing reproductive mode in T.melanosporum which makes it possible the presence of independent lineages within single populations or even within single natural truffle grounds. It is of remarkable applicative interest the finding that some populations can be simultaneously typed by two independent molecular markers, such AFLPs and SSRs are. It is therefore conceivable that, at least for few populations, distinctive genetic markers can be used as tools to trace truffles according to their proveniences.

References

Bertault, G., Raymond, M., Berthomieu, A., Callot, G. and Fernandez, D. (1998) Trifling variation in truffles. Nature 394, 734.

Nei, M. (1978) Estimation of the average heterozygosity and genetic distance from a small number of individuals. Genetics 89: 583-590