GENETIC VARIABILITY OF XANTHOMONAS FRAGARIAE STRAINS OBTAINED FROM FIELD OUTBREAKS AND CULTURE COLLECTIONS AS REVEALED BY REPETITIVESEQUENCE PCR AND AFLP
A. Stöger, D. Barionovi, A. Calzolari, R. Gozzi, W. Ruppitsch, M. Scortichini
The genetic variability of 43 Xanthomonas fragariae strains isolated in Italy during three different field outbreaks was compared with 20 representative strains previously isolated in Australia, USA, Brazil, Greece, New Zealand and Italy, and obtained from international culture collections. Typing was performed by repetitive-sequence PCR (rep-PCR) using BOX, ERIC and REP primer sets and amplified fragment length polymorphism (AFLP) analysis. Both techniques revealed that X. fragariae strains can be divided into different subgroups. No correlation between DNA amplification product patterns and geographic areas of origin was found. AFLP analysis revealed the existence of two major groups of strains related at a level of 73%. BOX, ERIC and rep-PCR assays identified five, three and two genotypes, respectively. The grouping of strains inferred by these two techniques was not mutually consistent. The strains of the three outbreaks in Italy showed in general a very similar banding pattern. No host specificity groups could be identified since two X. fragariae strains isolated from Fragaria vesca and one strain obtained from Fragaria chiloensis showed a similar banding pattern, like other strains isolated from Fragaria x ananassa. As determined by pathogenicity tests, no difference in virulence could be observed among strains of the classified groups. For the improvement of X. fragariae detection in strawberry propagative material, the relevant genetic variability of the pathogen should be taken into consideration.