Genetic diversity in Cronartium quercuum f.sp. fusiforme on loblolly pines in southern U.S.

Twelve random amplified polymorphic DNA (RAPD) markers were used to study genetic variability in three populations of Cronartium quercuum f.sp.fusiforme, the causal agent of fusiform rust on pines. Most of the variability (94%) was found within populations while 6% of the total variability was attributable to frequency differences between populations. The frequency of three markers was significantly different between regions of origin on an east-west transect. Three markers were completely absent from one of the populations while present in the others, and one marker was fixed in the western population but polymorphic in the eastern and central populations. However, no significant differences were observed when the western population was omitted from the analysis. The results suggest that C. quercuum f.sp.fusiforme is a highly heterogeneous pathogen with little geographic differentiation and underscores the importance of considering the populations structure of the pathogen in resistance breeding programs.