|Riassunto in Inglese:|
Tomato is attacked by many soil borne fungi. Among them, Pyrenochaeta lycopersici agent of corky-root, has became a serious problem since the ban of soil fumigation by methil bromide. Breeding for disease resistance is the most safe and effective control method. Knowledge of pathogen reproduction system and genetic variability provides insights into the relative importance of different forces that shape population genetic structure. This information is of interest for the development of successful breeding programmes for disease resistance. Knowledge of the genetic variability of P. lycopersici is scarce. RAPDs and PCR-RFLP of the IGS regions, analyzed on selected Italian isolates, showed low levels of genetic variability within this species. The occurrence of two molecular forms of this species, named Type I and Type II, has been observed and diagnosed by means of specific primers. In the present paper, Amplified Fragment Length Polymorphisms (AFLPs) was used for the first time for the analysis of genetic variability and structure of Italian populations of P. lycopersici. Population-assignment test with a Bayesan genotyping clustering, UPGMA-based cluster analyses and hierarchical analysis of molecular variance (AMOVA), were used. Based on the Fst value obtained, two different genetic groups have been identified. Within each group, a strong genetic differentiation among geographical locations was observed. The overall results may indicate clonality, low gene flow among populations and it is consistent with the hypothesis of strong founder effect and low dispersal ability of this pathogen. Further analyses are in progress on an additional set of populations and will allow to better explain the different level of genetic differentiation among geographical locations observed.