Department of Plant Pathology, University of Stellenbosch, Matieland 7602, South Africa
Dipartimento di Scienze e Tecnologie Fitosanitarie, University of Catania, Catania, Italy
University of California Cooperative Extension 1432, Salinas 93901
Cylindrocladium pauciramosum is well established in South America, and has recently been collected from nurseries in South Africa, Italy, and the United States. Isolates were compared with respect to the percentages of hermaphrodites and the respective mating types in the different samples. Based on these data, the effective population size could be determined for the different areas studied. All nurseries had mating type ratios significantly different from an idealized 1:1 ratio. In the South African nursery, the MAT-1 mating type was dominant, while the MAT-2 mating type dominated in other samplings. This is consistent with an introduction of a small starter population. High percentages of hermaphrodites also agreed with recent introductions into nurseries in Italy and the United States. Variability of DNA sequences of the 5′ end of the β-tubulin gene from a set of C. pauciramosum isolates from different geographic regions was low to high. Isolates from South Africa, the United States, and Australia had identical β-tubulin DNA sequences; this sequence was also found in the Italian sample, along with another unique group. Finally, a group of isolates obtained from South and Central America had the highest variation of all isolates investigated, and also included isolates that shared single nucleotide variations with another species, C. candelabrum. These findings suggest that C. pauciramosum most likely has a Central or South American center of origin.